Blood: plasma and formed element

 Blood 

Blood performs several vital functions of the blood; hence it has been frequently referred to as the seat of the soul. It distributes nutrients, oxygen, detoxicating compounds, and maintains a uniforms body temperature. It is a carrier of hormones which control and integrate the activities of the various organs. It conveys antibodies and cells that protect the body from invading pathogens and also transport drugs administered to the body so that they may produce their therapeutic effects on specific sites of ailment. 

The blood also collects the waste material generated by the body's metabolic activities. The blood can carry out its functions efficiently only if it is kept circulating in the body. This is affected by the heart which acts as a pump, and an intricate system of distributing pipes the blood vessels, viz, arteries, veins and capillaries. The heart and the blood vessels together form the cardio-vascular system.

Blood as a fluid Tissue: -

In human beings there is about 90 ml of blood per kilogram of body weight. However, this volume depends on the age and health of the Individual. Blood has a specific gravity of 1.05 to 1.06, and a pH of 7.4. It is made up of a fluid matrix called Plasma, and several types of cells termed formed elements. These two components separate when blood is centrifuged. The plasma forms 54% of the blood volume and the cells 45%. The latter is reffered to as the hematocrit or packed cell volume(PCV). The plasma contains many inorganic and organic substances. The formed elements consist of red blood cells(RBC) or erythrocytes, white blood cells(WBC) or leucocytes, and platelets or thrombocytes.

PLASMA

Blood plasma is the straw colored fluid obtained when all formed element are removed from blood. The ratio of plasma to formed elements is held relatively constant by the homeostatic controls of the body. The plasma contains inorganic salts with a dominance of chloride (Cl), sodium (Na+), and calcium (Ca++) ions, and lesser quantities of potassium(K+) and magnesium (Mg++) ions. Smaller concentrations of bicarbonate, sulphate, and phosphate, and traces of iron, copper, and iodine are also present.

The Plasma also contain glucose which is used as a principal energy source in cellular metabolism. A variety of other substances, such as amino acid, vitamins, lipids (neutral fats and cholesterol), hormones, urea, uric acid, and other metabolite waste produces are also present in the plasma. In addition, it contains dissolved oxygen, carbon dioxide, and nitrogen. Plasma also reflects certain abnormal conditions occurring in cells and tissue of the body. For example, within few hours following a heart attack, there is a noticeable increase in the level of the enzymes transaminase and lactic dehydrogenase in the plasma arising from the affected heart muscles. This has proved to be of significant value to a clinician is the diagnosis of heart attacks.

The plasma of a man contains about 70g proteins/L. Some of these proteins possess enzymic activity (e.g., phosphatases), While other function shows no activity at all. The function of the plasma proteins can be summarized as follow: -

1. Lipoproteins carry lipids and also transport lipid soluble vitamins and steroids hormones.
2. They are amphoteric compound because they act both as acids and bases. At the pH of human blood (pH- 7.4) proteins behave as acids and combines with cations such as Na+ and form a buffer, they are however, weak buffers.
3. Being macromolecules plasma proteins create a colloidal osmotic pressure in the blood which is higher than the colloidal osmotic pressure in the blood which is higher than the colloidal osmotic pressure in the interstitial fluid. This favors the passage of interstitial fluid into the plasma Finally (4) plasma, proteins, prothrombin and fibrinogen participate in blood clotting. 

FORMED ELEMENT 

The formed elements consist of the erythrocytes, leucocytes, and the thrombocytes.

ERYTHROCYTES: -

The red blood cells or erythrocytes are small (diameter: -7.5 in man and 9.0 in elephant) biconcave dices. Mammalian erythrocyte, except for the camel does mot possess a nucleus. In contrast, other vertebrates possess a nucleus. The erythrocytes are immobile and move with the flow of blood stream. The average concentration of erythrocytes is approximately 5000000/mm3 of blood in the adult human female. The erythrocytes are reddish in colour due to the presence of a respiratory pigment hemoglobin. Each erythrocyte contains an estimated 200 to 300 million molecules of hemoglobin. The latter serves to transport oxygen and, do some extent carbon dioxide, to and form the lungs. Hemoglobin is easily removed when the cell is broken (or lysed) by exposure to a hypotonic medium, or water. the resulting structure of the erythrocyte is called a "ghost" which consists of a network of protein and lipids.

The average life span of an erythrocyte in man is about 120days the old erythrocytes are continuously breaking down and new once are formed. The erythrocytes are destroyed by the phagocytic macrophages found in the reticulo-endothelial system (in bone marrow, spleen, liver, etc.). The porphyrin section of the hemoglobin is catabolized and formed bile pigment (bilirubin and biliverdin). However, most of the iron is retained in the bone marrow to be again incorporated into new erythrocytes.

LEUCOCYTES: -

The leucocytes are nucleated cells and are somewhat larger than the erythrocytes the white blood cells are also less abundant than the red blood cells. There are 5000 to 9000 leucocytes/mm3 of blood. An increase in the number of leucocytes above 10000/mm3 of blood is known as leukocytosis is caused by violent exercise, infection, hemorrhage, and a high protein diet. Leucopenia results from malnutrition, deficiency of vitamin B12, folic acid, and pyridoxine. 

The leucocytes are classified into granulocytes and agranulocytes depending on the presence or absence of granules in the cytoplasm.

Granulocytes are divided into three basic types, viz., neutrophils, eosinophils, and basophils. This classification of the granulocytes is based on the nuclear structure and affinity of the cytoplasmic granules to dyes (acid or base). In the neutrophils the cytoplasm is filled with fine uniformly distributed granules which do not show any affinity to either acid or basic dyes, and hence the name neutrophil. The nucleus is polymorphic divided unequally in 3-5 lobes and separated by deep indentations or by narrow strands of chromatin, therefore neutrophils are also referred to as polymorphocytes. These form 65-75% of the total leucocytes. The size of each neutrophil range from 10-12u. The eosinophils are loaded with granules which are relatively bigger in size than in the neutrophils. The granules show affinity to the acid dyes such as eosin the latter imparts them an intense red colour, and hence the name eosinophils. These are also referred to as acidophils. The nucleus is bilobed and the two lobes are connected by a thin stand of chromatin. The eosinophils form 2-4% of the total number of leucocytes. In the basophil, the cytoplasm takes an intense blue colored with basic dyes. The nucleus in the basophil is irregularly polymorphic. The basophils have the least representation in the total leucocyte count the normal percentage is only 0.15.

Agranulocytes are of two types, viz, lymphocytes and monocytes. The structure of the nucleus of agranulocytes is not polymorphic and is therefore, different form that of the granulocytes. Lymphocytes fall into two categories- small and large lymphocytes. The nucleus of the small lymphocyte is larger and it almost occupied the entire cell leaving only a peripheral cytoplasm, whereas the largest lymphocytes have relatively more cytoplasm. The lymphocytes form the second largest group of leucocytes; the small lymphocytes constitute about 25% and largest lymphocytes about 3% of the total leucocytes. The size of the small lymphocyte is about 7u, Whereas it is 10-12u in the large lymphocytes.

In monocytes the cytoplasm is more abundant in relation to the nucleus; the nucleus is ovoid, kidney shaped or with  many indentations. Moreover, characteristically, the nucleus is always placed eccentrically in the cells. The monocytes form 5-7% of total leucocytes. There size range from 10-15u. 

The average life span of leucocytes is two days. All leucocytes defend the body against invasion by microorganism which are engulfed and digested by the leucocytes by a process known as phagocytosis. Additionally, the lymphocytes form antibodies against proteinaceous matter gaining entry into the body. The relative ratio of the leucocytes changes during many diseases. This phenomenon is of great use to pathologists in diagnosis of diseases. For example, the concentration of eosinophils increases significantly during infection by worms, and in allergic conditions such as asthma and hay fever. 

Leukemia is very serious disorder of the body. This is a form of blood cancer and is characterized by an uncontrolled increase in the number of leucocytes (up to 1000000/mm3 of blood), with the appearance of immature forms in the blood stream. Leukemia is accompanied by anemia and is eventually fatal because the bone marrow cells that normally produce erythrocytes are displaced by leukemia cells. 

Thrombocytes or platelets: - In addition to the erythrocytes and the leucocytes, thrombocytes or platelets are another group of a formed the leucocytes, thrombocytes or platelets are another group of formed elements observed in the blood. These are small fragments (2-5u) of cells which lake nuclei, and function in blood clotting. They are oval in shape and have the capability of amoeboid movements. There are 250000 platelets/mm3  of blood. The life span of the thrombocytes is also very short perhaps only a few days in duration.

Lipids| fats| waxes| fatty acids| compound lipids| Derived lipids| cholesterol|

   LIPIDS   

Lipids are a very important heterogonous group of organic substances which are widely distributed throughout the plant and animal kingdom. The plant they are present in seeds, nuts and fruits, while in animals they are stored in adipose tissues, bone marrow and nervous tissues. Chemically they are various types of esters of fatty acids and alcohol. The addition to fatty acids and alcohols, some of the lipids may contain phosphoric acid, nitrogenous group and carbohydrate. Lipids are relatively insoluble in water and readily insoluble in water and readily soluble in organic solvents such either, chloroform, carbon desulphated benzene, hot alcohol etc. Bloor [1947] defined lipids as “naturally occurring compound which are insoluble in water, and soluble in one or more organic solvent such as benzene, chloroform, either acetone the so-called fat solvent on hydrolysis field fatty acids which are utilized by the living organisms.

CLASSIFICATION OF LIPIDS 

 Lipids are generally classified into three main classes: -

1. Simple Lipids

2. Compound Lipids

3. Derived Lipids

SIMPLE LIPIDS

Simple lipids are the esters of fatty acids with various alcohols. These can be further categorized into fats and waxes. Fats are triesters of glycerol and fatty acids. A fat in the liquid state is called oil. Waxes are the esters of fatty acids with long chain (higher mol.wt.) monohydric alcohols.

✒Fats: -

Fats are solids at room temperature. Chemically, fats are triglycerides since, three molecules of fatty acids condense with one molecule of glycerol, e.g. three molecules of stearic acid are linked to glycerol to yield glyceryl tristearate, a fat. 

If all the three molecules of fatty acids are similar, the product is a simple glyceride. If fatty acids molecules are different, it is called a mixed glyceride. Natural fats are largely composed of mixed glycerides. Since these glycerides have no acid or basic groups, they are often called natural fats. The melting point of fats depends upon the chain length and degree of saturation of fatty acids. The melting points of fats are always higher than the solidification point, e.g. tristearin melts at 720C but solidifies on cooling at 520C.Fats develop unpleasant odor on aging, this is due to auto oxidation of fat. This is called rancidification.

The chemical changes that occur during rancidification are called rancidity. Fats which are liquid at room temperature are called oils. Oils are also esters of fatty acids and glycerol, but the fatty acids found in oils are unsaturated fatty acids. The unsaturated fatty acids have one or more double bonds. They have low melting point and are insoluble in water. Hydrolysis of fats with alkali or enzymes lipase yields fatty acids and glycerol. When the fats are hydrolyzed with alkali, the few fatty acids react with alkali to form salts. These salts are soaps and this process is called saponification.

✒Waxes: - 

Waxes are another class of simple lipids. These are the esters of fatty acids with high molecular weight alcohol. Waxes contain one molecule of fatty acids and one molecule of alcohol. The bees wax, the fatty acid constituent is a smaller chain acid, palmitic acid and [160C] and alcohol is myristic palmitate. Ameltolides found in the seeds of abelmoschus esculentus is a hay hydro nil acid and is responsible for the characteristic smell of the seed. Being highly insoluble in water and having no double bonds in their hydrocarbon chains, waxes are chemically insert. And very resistant to atmospheric condition also not digested by the fat splitting enzymes. They can be split slowly with hot alcoholic KOH, however. They also have higher melting point. They serve as protective coating onfruits and leaves. They play on important role in provide water barrier for insects, birds and animals. They are used in furniture polishing.

✒Fatty Acids: - 

Fatty acids are obtained from the hydrolysis of fats. Since all the fats contain glycerol, their properties differ according to the nature of fatty acids present in them. A fatty acid can be defined as an organic acid that occurs in a natural triglyceride and is a monocarboxylic acid ranging in chain length from C4 to about 24 carbon atoms. A few have branched chain or contain hydromel group or have a cyclic chain at the end. Fatty acids that occur in natural fats usually contain an even number of carbon atoms, one carboxylic group and are straight chain derivatives. On the basis of presence or absence of double bonds, fatty acids may be classified into two main classes.

1). Saturated fatty acids (saturated with hydrogen)

2). Unsaturated fatty acids 

1). Saturated fatty acids: - 

The fatty acids which do not contain any double bond are called saturated fatty acids. The general formula is Cn H2n+1 COOH e.g. Butyric acid C3 (CH2)2 COOH. The most abundant saturated fatty acids in nature are palmitic acid (C18) and stearic acid (C16). The saturated fatty acids are straight chain acids. In addition to these straight chain acids, there are some branched chain acids, with odd or even number of carbon atoms.eg. Isopalmitic acid, anti-isopalmitic acid and tuberculostearic acid.

2). Unsaturated fatty acids: - 

The fatty acids which contain one or more double bonds are called unsaturated fatty acids. On the basis of number of double bonds, the unsaturated fatty acids may be divided into two groups.

✔Monosaturated fatty acids: - having one double bond e.g. crotonic acid, oleic acid, palmitoleic acid, nervonic acid etc.

✔Polyunsaturated fatty acids:-having more than one double bonds e.g. linoleic acid, eleostearic acid etc.

In most of the monosaturated fatty acids there is a single bond lying between carbon atoms 9 and 10. This is designated as ∆9. The symbol ∆ with the superscript number nine (9) indicates the positions of the double bond. When there are more than one double bond (polyunsaturated fatty acids), the additional bonds occur between the ∆9double bond and the methyl terminal end of the chain. 

The symbol 18:3 signifies that there are three double bonds and symbol ∆9,12,15 signifies that the position of double bonds are between carbon atom 9 and 10, 12 and 13 and 15 and 16. Presences of double bonds in the fatty acids lower their melting point considerably. Most plant fats contain unsaturated fatty acids as oleic acid and linoleic acid and hence they are liquid at room temperature. Contrary to this animal fats have more of saturated fatty acids and hence solid at room temperature.

Essential and Non Essential Fatty Acids: - 

Essential fatty acids: - The fatty acids which cannot be synthesized by human body but are essential for the normal maintenance of the body are called essential fatty acids .These fatty acids must be included in our diet. Three polyunsaturated fatty acids, linoleic acid, linolenic acid and arachidonic acid are the essential fatty acids.

Non essential fatty acid: -These are the fatty acids which can be synthesized by our body. Thus they need not be included in our diet. They are unsaturated fatty acids and are synthesized from their corresponding structural fatty acids by introducing a single bond e.g. palmitoleic acid and oleic acid.

COMPOUND LIPIDS: -

Compound lipids contain some additional groups or elements besides fatty acids are alcohol. The addition group may contain phosphorus, nitrogen, Sulphur or it may be a protein. Compound lipids can be categorized into the following: Phospholipids, Glycolipids, Other compound lipids.

Phospholipids: - 

Phospholipids are those compound lipids which contain a phosphorus atom. Phosphorus is widespread in bacterial animal and plant tissues and their general structures are quite similar. These have been termed as amphipathic and compound since they process both polar and non-polar function.

In addition to phosphorus, phospholipids may also contain nitrogen as a key component. There are various types of phospholipids including, lecithin, cephalins, plasmalogens, phosphoinositide and phosphosphingosides.

Lecithin: -

Lecithin is widely distributed in nature. In animals it is found in liver, brain, nerve tissues, sperm and egg yolk. In plant it is abundant in seeds and sprouts. On hydrolysis, lecithin yields glycerol, fatty acids, phosphoric acid and nitrogenous base- choline. It is also called phosphatidyl choline. The fatty acids commonly found in lecithin are palmitic, stearic, oleic, linolenic and arachidonic acids. Lecithin is  yellowish grey solid which is soluble in with soluble in ether and alcohol but insoluble in acetone. On exposure to air they rapidly darken colour and absorb water, forming dark grassy mass. Lecithin are broken down by the enzyme lecithinase to lysolesithin which is present in venoms of bee and cobra. When injected into the blood, lysolecithins cause rapid hemolysis of the red blood cells. e.g. lecithin( phosphatidyl choline) 

Cephalins: -

Cephalins are found in animal tissues in close association with lecithin. They are also found in soya bean oil. The basic difference between cephalins and lecithin is the nature of nitrogenous base. Cephalins contain ethanolamine in place of choline. The fatty acid components of cephalins are stearic, oleic, linoleic and arachidonic acid. They are less soluble in alcohol then lecithin.

PLASMALOGENS 

Plasmalogens are abundant in brain and muscles they are also found in the seeds of higher plants. Structurally, they resemble lecithin and cephalins except in having an aldehyde group attached to ex – carbon atoms of glycerol. They are soluble in all lipid solvents.

Phosphoinositides: -

They are present in brain tissues and nervous tissues. They can be either mono or diphosphoinositides. Monophosphoinositides contain hexahydric alcohol inositol. The name lipoinosital was also proposed for them.

PHOSPHOSPHINGOSIDES: - 

These lipids are abundant in lacking in plant and microorganisms. In these lipids glycerol is replaced by an 18 carbon unsaturated amino alcohol called ‘sphingosine’. On hydrolysis they yield fatty acids, phosphoric acid, choline and sphingosine

Glycolipids: -

Glycolipids are compounds containing  carbohydrates and high molecular weight fatty acid like sphingosine but no phosphoric acid. These are of two types:- 

i) Cerebrosides 

ii)Gangliosides

✔Cerebrosides: They occur in large amount in brain and myelin sheath of nerves. The structure of cerebrosides is somewhat similar to sphingomyelin. Here the fatty acid ceramide is linked either to galactose or glucose.

✔Gangliosides: These are found in ganglion cells of nervous tissues and also in parenchymatous tissues like spleen and RBCS, They are the most complex glycosphingolipids. They are ceramides with attached oligosaccharides that include at least one sialic acid residue.

Other compound lipids: -

Sulfolipids: - Lipids containing sulfur, widely distributed in plant (localized in chloroplast) and bacteria. 

Lipoprotein: - They are the component of membranes found in the membranes of mitochondria, ERI, The lipid component consists of triacylglycerol, phospholipids and cholesterol. The protein components of lipoprotein have a relatively high portion of non polar acid residues. 

DERIVED LIPIDS: - 

Derived lipids are the product of hydrolysis of simple lipids and compound lipids and in addition other lipid like compounds such as steroids, terpenes, fatty acids, alcohols, carotenoids, essential oils etc. 

Steroids: - 

Steroids are the derivatives of cyclopentanoperhydrophenanthrene, a compound consisting of four fused non planer rings. They are named as A, B, C and D. The rings A, B and C are hexagons and are called cyclohexane rings while D is a pentagon and is called cyclopentane.

Sterols: -

The steroids may have one or more alcoholic groups. The steroids having alcoholic groups are called sterols. They are crystalline compounds and differ from alcohols in being solids that is the reason they are called sterols. Steroids are widely distributed in plant, animals and microorganism. They are found in cell membranes and other cellular component containing lipids. Unlike other lipids, sterols cannot be saponified and by this process they can be separated from other lipids. Ergosterol is present in food in small amount. It has been isolated from parasitic fungus Claviceps pupurea (Ergon) growing on rye plants. Other plant sterols are spina sterol obtained from spinach and cabbage, stigmasterol from coconut and soyabeans and sitosterol from cereal seeds.

Cholesterol: - 

The best known animal sterol is cholesterol, which is a major component of animal plasma membrane. It is classified as sterol because of its C30H group It is present in relatively high concentration in nervous tissues and in bile. Cholesterol is a crystalline solid with rhombic crystals and its solution is levorotatory. It has a high melting point.

In mammals, cholesterol is the metabolic precursor of steroid hormones – adrenocorticoids and sexsteroids

Adrenocorticoids: - 

They are secreted by the adrenal cortex hormone contains – glucocorticoids, aldosterone, cortisterone, desoxycortisterone adrenosterone and other mineral corticoids influence a wide variety of vital functions.

Sex steroids: -

The testes secrete testosterone, andosterone and adrenosterone, while estrogens and progesterone are secreted by the ovary. They affect sexual development and functions.

SOURCES OF LIPIDS 

Lipids are widely distributed in plants and animals. Common sources of fatty acids are butter, coconut oil, animal fats and some bacteria. Lecithin, a type of phospholipids is found in liver, brain, nerve tissue, sperm and yolk sac in animals while in plants it is abundant in seeds and sprouts. Similarly other phospholipids and glycolipids are also found in animal tissues like brain, muscles and nervous tissues. Terpenes and carotinoids are types of derived lipids which are exclusively of plant origin

BIOLOGICAL SIGNIFICANCE OF LIPIDS

✔ Rich source of energy: fats provide food of high calorific value (1g fat produces about 9.3 kilo calories of heat).

✔As food reserve: Fats are stored in body as reserve food material, because these could be readily stored in the body on account of insoluble character sticks. Triglycerides stored in adipocytes (fat cells) of adipose tissue are the principal fat reserve.

✔ As heat insulators: Fats deposited in the subcutaneous tissues act as insulators conserving body heat.

✔Solvent: Lipids act as a solvent for fat soluble vitamins like vitamin A, D and E.

✔Structural constituents: Phospholipids, glycolipids and sterols are structural components of all the membrane system of cell (i.e. cell membrane, nuclear membrane, membranes of the endoplasmic reticulum etc.)

✔Fat transport: Phospholipids play an important role in the absorption and transportation of fatty acids.

✔Hormone synthesis: Adrenocorticoids, sex hormones, vitamin D and cholic acids are synthesized from cholesterol.

✔As shock absorber: The fat deposited around the visceral organs and underneath the skin acts as cushion and absorbs mechanical shocks.

✔As electric insulators: Myelin sheath around medullated nerve fibres forms an electric insulation.

✔Prostaglandins: They control local activities in the body.

✔Protective layers: Lipids form a protective waxy covering on the aerial parts of plants to check loss of water by evaporation.

✔Thrombokinase: helps blood clotting.

✔Leukotrienes: a group of eicosanoid helps in respiration.

✔Some isoprenoids form insect hormones.

✔Some in isoprenoids form volatile oil and pigments. Natural rubber is also an isoprenoid.

✔Glycolipids help in cell recognition.

✔Complex lipids form phospholipid bilayer of plasma membrane.

✔Steroid act as hormones and neurotransmitters in mammals

DEFICIENCY DISEASES OF LIPIDS 

The deficiency of lipids in human body causes dry, scaly skin, hair loss, loss of mensuration, cold intolerance, power resistance to infection and bruising, poor growth, poor wound healing and low body weight.

carbohydrates| Krebs cycle| monosaccharides| oligosaccharides| polysaccharides| glycolysis| electron transport system|

  CARBOHYDRATES  

Carbohydrates are the most abundant class of biomolecules in nature. They are widely distributed in plants and animals. Carbohydrates are the compounds of carbon, hydrogen and oxygen with empirical formula Cn(H2O)n, where n represents number of carbon atoms. However, not all the carbohydrates have this empirical formula; some also contain nitrogen, phosphorus and Sulphur. They are also called hydrates of carbon because in them hydrogen and oxygen occur in the radio of 2:1, similar to that found in water. Carbohydrates are broadly defined as polyhydroxy aldehydes or ketones and their derivatives or substances that yield one of these compounds on hydrolysis or in other words they are defined as the compounds having either an aldehyde (-CHO) or a ketone (=CO) group or a modified aldehyde or ketone group and other carbon atoms with alcoholic (-OH) groups.

CLASSIFICATION OF CARBOHYDRATES 

Carbohydrates are classified into three main classes: -

1). Monosaccharides: These are the simplest carbohydrates, cannot be hydrolyzed into small molecules.

2). Oligosaccharides: This class includes, the carbohydrates comprise of short chains of monosaccharide units, most common are disaccharides comprise of two monosaccharide units.

3). Polysaccharides: This class includes the carbohydrates consists of long chains of monosaccharide units generally hundreds or thousands.

MONOSACCHARIDES: -

Monosaccharides are simple carbohydrates having single or one saccharide (Sugar) molecule. These cannot be hydrolyzed further into simpler molecules. They are colourless crystalline, sweet tasting. substances soluble in water, sparingly soluble in alcohol and insoluble in ether. They are reducing agent as they reduce the oxidizing agent and get oxidized at the carboxyl group. They are called monomers and form structural units of oligo and polysaccharides. The number of carbon atoms in monosaccharides varies from 3 to 7. The carbon atoms form an unbranched straight chain, joined together by single covalent bonds. On the basis of number of carbon atoms monosaccharides are classified into 5 classes: -

Trioses: with three carbon atoms (C3H6O3)

Tetroses: with four carbon atoms (C4H8O4)

Pentoses: with five carbon atoms (C5H10O5)

Hexoses: with six carbon atoms (C6H12O6)

Heptoses: with seven carbon atoms (C7H14O7)

A monosaccharide molecule has two functional groups: A carbonyl (-C=O) group in which oxygen is attached to carbon atom by a double bond. Hydroxyl (-OH) groups which are attached to all other carbon atoms of the chain. On the basis of the position of the carbonyl (-C=O) group at the chain, monosaccharides are divided into two families: 

A). Aldoses

B). Ketoses

A). Aldoses: If the carbonyl group is present at the end of the carbon chain, aldehyde (-CH=O) group is formed and the sugar is called as an aldose sugar.

B). Ketoses: If the carbonyl group is present at any other position, ketone (-C=O) group is formed and the sugar is called as ketose sugar.

Glyceraldehyde and dihydroxyacetone are the simplest monosaccharides with three carbon atoms. Here glyceraldehyde is an aldose as it contains an aldehyde group while, dihydroxyacetone is a ketose because it contains a keto group. Glucose is a hexose sugar with six carbon atoms (C6H12O6). It is an aldose as it contains an aldehyde group, while fructose is a keto hexose sugar because it contains a keto group.

OLIGOSACCHARIDES: -

Oligosaccharides are composed of few monosaccharide units (2-20). During union of monosaccharide units, water molecule is eliminated and the units are linked through an oxygen bridge. This chemical bond that joins the two monosaccharide units is called a glycosidic bond. Depending upon the steric configuration at C1, which is involved in the formation of glycosidic linkage of monosaccharide unit, the bond is called α- and β- bond. The natural source of oligosaccharides is green plants. They are crystalline substances and readily soluble in water, most of them are obtained as colourless solids. Oligosaccharides are classified according to the number of their constituent monosaccharide units. In the modern system of nomenclature these are named according to the name of their constituent monosaccharide units and the position of glycosidic bond such as:

1). Disaccharides (2 sugar units), 

2). Tri-saccharides (3 sugar units), 

3). Tetra-saccharides (4 sugar units) etc.

 Out of these most common are disaccharides.

1). Disaccharides: - Disaccharides consists of two monosaccharide units covalently bound to each other with a glycosidic bond. Their empirical formula is C12H22O11. These can be hydrolyzed to yield their free monosaccharide compounds by boiling with dilute acid. Following are the examples of disaccharides.

✔ Maltose: -It is the simplest disaccharide, composed of two units of D-glucose joined together through their 1 and 4 carbon atoms. It does not occur in nature and also called as malt sugar. It is the product of hydrolysis of starch by the enzyme amylase. Maltose is hydrolyzed to two molecules of glucose by the intestinal enzyme maltase. 

✔ Sucrose: -It is the most abundant disaccharide, made up of glucose and fructose also known as cane sugar. It is obtained commercially from cane or beet. It is very sweet, crystalline and freely soluble in water. It can be cleaved into its components by the enzyme sucrase.

✔ Lactose: It occurs naturally only in milk thus also known as milk sugar. It is made up of glucose and galactose units joined together through carbon 1 of galactose and carbon 4 of glucose. It is not much sweet to taste and hydrolyzed to its monosaccharides by enzyme lactase in human beings.

Fig: - example of disaccharides

2). Trisaccharides: -These are composed of three molecules of monosaccharide units. Examples of trisaccharides are: 

✔ Raffinose: - It is made up of glucose, galactose and fructose units. It is found in sugar beet and cotton seed meal and in some fungi.

✔ Gentianose: -It is composed of one unit of fructose and two units of glucose. It is found in rhizomes of several gentian species.

3). Tetra-saccharides: - These are composed of four molecules of monosaccharide units. Example of tetra saccharide is-

✔ Stachyose: - It is composed of two units of galactose, one unit of glucose and one unit of fructose. It is found in the hair cot beans.

POLYSACCHARIDES: - 

Polysaccharides are composed of several monosaccharide units linked together by glycosidic bond. Polysaccharides are tasteless and colourless amorphous powder which are little soluble in water, although some may form colloidal solutions. The most common monosaccharide units in polysaccharides are glucose, although fructose, galactose and other hexoses also occur. If all the monosaccharide units are the same in a polysaccharide, it is called a homopolysaccharide. For example, starch, cellulose and glycogen, they all are polymers of glucose. If the monomeric units are different in a polysaccharide, it is called a heteropolysaccharide. For example, Hyaluronic acid, made up of alternating residues of uranic acid and N-acetyl glucosamine. On the basis of their function, polysaccharides are classified into two classes: -

1). Storage polysaccharides 

2). Structural polysaccharides.

1). Storage Polysaccharides: Polysaccharides are stored as reserve products in many tissues. They occur as starch in plant cells and as glycogen in animal cells.

✔ Starch: Starch is a storage polysaccharide as it is the reserve food material in the plants. It is a homopolysaccharide made up of glucose units. It is especially abundant in tubers such as potatoes, in seeds especially corn, but most plant cells are able to produce starch. It contains two types of glucose polymers- α-amylose and amylopectin. Α-amylose consists of long chain of D-glucose units linked by α (1→4) linkage while amylopectin is a branched chain of D-glucose units. The glycosidic linkages in linear chain are α (1→4) but at the branch points these are α (1→6) occurring every 24 to 30 residues.

✔ Glycogen: Glycogen is a storage polysaccharide as it is the major reserve food material in animals, the counterpart of starch in plant cells. It is a homopolysaccharide made up of glucose units. It is especially abundant in the liver, where it may constitute as much as 7% of the wet weight; it is also present in the skeletal muscle. Glycogen is a branched polymer of glucose in which glucose residues are linked by α(1→4) and α(1→6) glycosidic linkages just like in amylopectin, but glycogen is more extensively branched (on average every 8 to 12 residues) and more compact than starch.

2). Structural Polysaccharides: Polysaccharides are involved in the structural organization of many tissues in microorganisms, higher plants and animals. They occur as cellulose in plant cells and as chitin in animal cells.

✔ Cellulose: Cellulose is a major structural polysaccharide in plant cells and also present in some microorganisms. It is a fibrous, tough and water insoluble substance. Cotton is almost pure cellulose while wood is largely made up of cellulose. Cellulose is a linear, unbranched, homopolysaccharide of 10,000 or more D-glucose residues, connected by β (1→4) glycosidic linkage. However, cellulose resembles with amylase and the main chain of amylopectin of glycogen but in those, the linkage is α (1→4) glycosidic linkage.

✔ Chitin: Chitin is the structural component of exoskeleton of invertebrates such as insects and crustaceans. It is also present in the cell-walls of fungi and many algae. Chitin is a homopolysaccharide made up of N-acetyl-D-glucosamine linked by β (1→4) glycosidic linkage.

METABOLISM OF CARBOHYDRATES: -

Carbohydrates are the major source of energy in the organisms. Dietary carbohydrates mainly consist of polysaccharides (starch) and disaccharides (sucrose, lactose and maltose). These are hydrolyzed into monosaccharides and are absorbed in the blood. Glucose is an important monosaccharide which served as the major metabolic fuel of the cell and tissues. Non-glucose monosaccharides are also converted into glucose. Glucose is metabolized in different ways to produce energy in the body. The main pathways of carbohydrates metabolism are –

I. Glycolysis 

II. Citric acid cycle

III. Glycogenesis

IV. Glycogenolysis

V. Gluconeogenesis 

VI. Pentose Phosphate Pathway

I). Glycolysis: -

Glycolysis is a process in which one molecule of glucose is converted into two molecules of pyruvate. The pathway is also known as Embden-Meyerhof Parnas (EMP) Pathway after two pioneer investigators Gustav. Embden and Otto Meyerhof. Glycolysis occurs in the cytoplasm of the cell and virtually in all tissues. The process is completed in 10 steps and each step is catalyzed by a specific enzyme. Glycolysis is divided into two phases. In the first phase, one molecule of glucose is converted into two molecules of glyceraldehydes-3-phosphate. The process requires 2 molecules of ATP. In the second phase the molecules of glyceraldehydes-3-phosphate are converted into pyruvate with the release of 4 ATP and 2 NADH molecules. Steps of glycolysis are as follows: -

End products of glycolysis 

✒From one molecule of glucose two molecules of pyruvate are formed.

✒2 ATP molecules are used while 4 ATP molecules are formed. Therefore, there is net gain of 2ATP molecules.

✒2H+ atoms are formed. These are accepted by NAD, which changes into NADH+H+. Hydrogen ions are transferred to electron transport system.

Fate of pyruvate: -

The pyruvate formed, as a result of glycolysis, can be further metabolized via any of the three catabolic pathways: -

I. Under aerobic conditions, pyruvate is oxidized completely to yield CO2 and H2O by citric acid cycle.

II. Under anaerobic conditions, in some microorganisms and under hypoxia in skeletal muscles, pyruvate is reduced to lactate via lactic acid fermentation.

III. In some plant tissues invertebrates and microorganisms under hypoxic or anaerobic conditions pyruvate is converted into ethanol and CO2 via ethanol (alcohol) fermentation.

Citric Acid Cycle: -

Under aerobic conditions pyruvate is completely oxidized to yield CO2 and H2O. pyruvate is first converted to acetyl Co-A which is then oxidized to produce CO2 and H2O. The whole process occurs in a cyclic manner and is called citric acid cycle. The cycle is also known as TCA cycle (Tricarboxylic acid cycle) or Krebs cycle after its discoverer Hans Krebs. The enzymes for TCA cycle located in the mitochondrial matrix.

During glycolysis each glucose molecule yields 2 molecules of pyruvate, and 8 ATP are gained. Hence when these two molecules of pyruvate undergo complete oxidation by TCA cycle 24 ATP are formed. In addition, 2NADH are formed during the formation of acetyl Co-A by pyruvate through dehydrogenase complex which yields 6 ATP molecules. Thus, complete oxidation of one molecule of glucose will yield 38ATP molecules (glycolysis 8, Pyruvate dehydrogenase complex 6, TCA cycle24).

Glycogenesis: -

Glycogenesis is the process of formation of glycogen from glucose. The major sites of glycogenesis are liver and muscles, but it can occur in every tissue in the body to some extent. Glycogenesis is a very important process as excess of glucose is converted to glycogen and is stored in this form for utilization at the time of requirement.

For synthesis of glycogen, a pre-existing glycogen chain (glycogen primer) is required. UDP-G transfers the glucose molecule to a pre-existing glycogen primer. C-1 of the glucose of UDP-G forms a glycosidic bond with the C-4 of a terminal residue of glycogen primer in the presence of enzyme glycogen synthase. UPD is liberated in this process. In this way an existing glycogen chain is repeatedly extended by one glucose unit at a time by the successive α 1-4 linkage. Glycogen synthase is a principal enzyme which regulates glycogen formation. 

Glycogen synthase can add glycosyl residue only if polysaccharide chain already contains more than four residues. When the chain has become minimum of 11 glucose residues, another enzyme, branching enzyme transfers a part of α 1-4 chain (at least 6 glucose residues) to a neighboring chain to form α 1-6 linkage, thus forming a branching point in the molecule. The branches now grow further by further addition of α 1-4 glycosyl units and further branching. The glycogen formed is stored in liver and muscles.

Glycogenolysis: -

The breakdown of glycogen to glucose is called glycogenolysis. When the blood glucose level falls, glycogen is broken down to glucose to maintain the normal level of blood glucose.

The first step in the breakdown of glycogen is catalyzed by the enzyme glycogen phosphorylase which catalyzed the cleavage of terminal α1-4 linkage of glycogen to remove one glucose residue as glucose-1-phosphate. 

The removal of glucose residues continues until about four to five glucose residues remain on either side of the α1-6 branch. Further degradation by glycogen phosphorylase can occur only after the debranching enzyme (a bifunctional enzyme), catalyzes two successive reactions: -

1). The transferase activity of the enzyme shifts a block of three glucose residues from the branch to a nearby non reducing end to which they reattached in α 1-4 linkage.

2). Then the 1-6 glucosidase activity releases a single glucose residue remaining at the branched point in α-1-6 linkage. After this glycogen phosphorylase activity can continue. Glucose1-phosphate formed on the phosphorylate cleavage of glycogen is converted into glucose 6-phosphate by phosphoglucomutase. The glucose 6-phosphate formed from glycogen in muscles enters into glycolysis and serve as an energy source to support the muscle contraction. In liver, enzyme glucose 6-phosphatase cleaves the phosphoryl group from glucose 6-phosphate to form free glucose which release into the blood when the blood glucose level drops.

Gluconeogenesis: -

It is the formation of glucose from non-carbohydrate sources, such as lactate, pyruvate, citric acid cycle intermediates and most of the amino acids. Gluconeogenesis mainly occurs in liver and to a lesser extent in kidney. It takes place only when carbohydrates are not available in sufficient amount from the diet. Though most of the reactions of gluconeogenesis are the reversal of glycolysis, there are certain reactions which are specific to gluconeogenesis. These are:

1). Conversion of pyruvate to phosphonyl pyruvate,

2). Conversion of fructose 1, 6, bisphosphate to fructose 6-phosphate,

3). Formation of glucose from glucose 6- phosphate 

1. Conversion of pyruvate to phosphonyl pyruvate:

 In this step pyruvate is first converted to oxaloacetate, which is then converted to phosphonyl pyruvate.As oxaloacetate is formed inside the mitochondria it must come out to the cytosol for conversion to phosphoenol pyruvate because the enzyme phosphoenol pyruvate kinase is present in cytosol. As oxaloacetate is not permeable to mitochondria it is converted to malate and cross the mitochondria. In the cytosol malate is again converted to oxaloacetate. Oxaloacetate can also combine to acetyl co-A in the mitochondria to form citrate which is permeable to mitochondria. In the cytosol, citrate is again converted to oxaloacetate. Once phosphoenol pyruvate is formed it goes into reverse glycolytic pathway to form fructose 1, 6, bisphosphate.

2. Conversion of fructose 1, 6, bisphosphate to fructose six phosphates: 

3. Formation of glucose from glucose 6 phosphate

Glucose produced by gluconeogenesis in liver or kidney is released into blood stream to be carried to the tissues.

Pentose phosphate pathway 

Pentose phosphate pathway (PPP) is also known as phosphogluconate pathway (PGP) and the hexose monophosphate shunt (HMP), operates in the cytosol o the cell.

The pathway serves following purpose:

✅ It provides cytosolic NADPH for use in biosynthesis of fatty acids and steroids,

✅ It synthesizes ribose phosphate, a precursor of the nucleotide biosynthesis.

✅The pathway ultimately yields glyceraldehyde 3-phosphate which can be then oxidized to produce ATP.

✅In dark reactions of photosynthesis, a variation of pentose phosphate pathway leads to the synthesis of glucose.

Pentose phosphate pathway comprises of some oxidative and some non-oxidative reactions. In oxidative phase, glucose 6-phosphate is converted to a pentose sugar, ribulose 5-phosphate with the elimination of NADPH and CO2. In non-oxidative phase, ribulose 5-phosphate molecules undergo a series of conversions and ultimately produce fructose 6-phosphate and glyceraldehyde 3-phosphate.

ELECTRON TRANSPORT SYSTEM OR RESPIRATORY CHAIN

During the process of respiration, both oxidation and reduction go on simultaneously. When a substance releases hydrogen, it is called hydrogen donor and said to be oxidized. The substance accepting hydrogen is called hydrogen acceptor and is said to be reduced.At various stages in glycolysis, in oxidation of pyruvic acid and Kreb’s citric acid cycle, hydrogen atoms are released.

✅ In glycolysis: 2 x 2H,

✅During decarboxylation of pyruvic acid and formation of acetyl coenzymes A: 2 x 2H,

✅During Kreb’s cycle: 2(4x2H.)

Each hydrogen atom consists of one proton and electron 2H→2H +2e. Protons are soluble in water but not the electrons. The protons are released into aqueous solution of cell, the electrons are accepted by the electron acceptors of electron transport system. ETS or electron transport system is a system of enzyme and coenzymes present in the inner mitochondrial membrane. These enzymes and coenzymes act as hydrogen and electron accepters. In ETS several hydrogen and electron acceptors are present alternately. Hydrogen and electrons are passed from one acceptor to another. Finally, hydrogen is accepted by molecular oxygen and water is formed.

There are three major classes of enzymes involved in electron transport in mitochondria,

(i) Pyridine linked dehydrogenase catalyzes   reversible transfer of electron from intermediates of TCA cycle to NAD+ or NADP+ and produce NADH or NADPH respectively,

(ii) The flavin linked dehydrogenase catalyses transfer of electrons from either succinate or NADH to FMN or FAD and

(iii) The cytochromes acting in series and transferring electrons from flavoproteins to molecular oxygen Oxidative Phosphorylation in Electron Transport System Electrons released during transport of H+ along ETS are accepted by electron accepters of ETS and are passed on to Fo-F1 complex or ATPase complex where ADP is phosphorylated into energy rich ATP molecules. This process of ATP synthesis from ADP and inorganic phosphate (pi) during oxidation of acetyl coenzyme-A is called oxidative phosphorylation. During this oxidation energy is released in graded sequence. Some of this energy is utilized by F1 particles containing there coupling factors and ATPase enzyme for the synthesis of ATP molecules from ADP.

Thus, for the reduction of one molecule of oxygen, six protons are translocated from matrix to peri mitochondrial space. This creates an increase of proton concentration outside the inner membrane and sets up a proton gradient or electrical potential difference. The resulting potential difference forces the proton to return towards the mitochondrial matrix. They pass through the coupling factors of complex V or Fo-F1 complex or ATPase complex. This provides energy for synthesis of ATP for every pair of protons driven inwards one ATP molecule is synthesized.

SOURCES OF CARBOHYDRATE 

Carbohydrates are the most abundant biological molecules. They are widely distributed molecules in plants and animals both tissues. Plants are considerably richer in carbohydrate in comparison of animal. Plants synthesize glucose during photosynthesis from carbon dioxide and water. It is stored in the form of starch. Cellulose, pectin and lignin are the common structural polysaccharides present in plants, which forms the plants framework, which is generally present in seeds, tubers and rhizomes of the plants. In animal cells, glycogen is present as a storage polysaccharide. Glucose is present in the human blood in a concentration of 1g/L. Chitin, hyaluronic acid and chondritin sulphates serve as structural polysaccharides in animals, present in the shells of lobsters, crabs, insects and in the cartilage, adult bones heart valves and cornea. Lactose occurs naturally in milk of mammals also detected in the flowers of some plants

BIOLOGICAL SIGNIFICANCE OF CARBOHYDRATES 

• The most important information role of carbohydrates is the production of energy in the form of ATP both in plants and animals, the energy being derived as a result of their oxidation.
• They are indispensable for living organisms, serving as skeletal structures in plants (e.g. cellulose, hemicellulose, lignin and pectin) and animals (e.g. Chitin, hyaluronic acid chondroitin sulphates)
• They also occur as food reserves in the storage organs of plants (e.g. seeds, tubers and rhizomes) in the form of starch and inulin. Sucrose (sugar cane, beet), glucose (grapes) and fructose (fruits) are also stored. In animals, storage form of carbohydrate is glycogen. Glucose is the most important carbohydrate. The bulk dietary carbohydrates are absorbed in the form of glucose, which is present in blood as a most common carbohydrate in a concentration of 1g/L.
• Deoxyribose and ribose sugar form part of the structural framework of DNA and RNA.
• Carbohydrates also play role as mediators of cellular interactions.
• They play a key role in the synthesis of acids, lipids, fatty acids and steroids.
• They also serve to lubricate skeletal joints to provide adhesion between cells and to confer biological specificity on the surface of animal cells.

DEFICIENCY DISEASES OF CARBOHYDRATES 

1. Acidosis: In carbohydrate starvation, there is a shift from glycolysis (breakdown of glucose) to lipolysis (breakdown of lipids) and ketogenesis for energy needs. The resulting product, keto acids increase acidity in the blood and other body tissues. These changes in the pH of arterial blood outside 7.35 pH -7.45 pH result in irreversible cell damage.
2. Ketosis: Carbohydrate deficiency causes the production of ketone bodies in liver formed by the breakdown of fatty acids and by the deamination of amino acids, leading to a state of ketosis. Ketosis results in chronic dehydration and reduced body secretions.
3. Hypoglycemia: The non-availability of glucose due to severe lack of carbohydrate causes drop in the blood sugar levels. It occurs when blood glucose level drop under 70 mg/L with typical symptoms like giddiness, fatigue and distress.
4. Constipation: Dietary fiber is an essential component of carbohydrate food, which is known to prevent recto colon cancer and help digestion. The absence of dietary fiber can cause constipation.

Proteins| classification | structure and organization| deficiency diseases of proteins|

    PROTEINS    

Proteins are the highly complex chemical compounds present in all living organism. These are the high molecular weight polypeptides, composed of carbon, hydrogen, oxygen, nitrogen, Sulphur and phosphorus. Proteins are the most abundant and essential constituents of living cells. All the basic functions of life depend upon specific proteins. The term protein was first suggested by Swedish chemist Berzelius in 1938 and derived from the Greek word “proteins” meaning ‘first’. Gerardus Mulder for the first time used the term in 1840 and referred it to the complex organic nitrogenous substance found in the cells of living organisms. Proteins are the most significant compound in living beings depending upon their chemical and physical structures they are involved in wide variety of functions i.e. catalysis, conduction, contraction, structure, nutrition, binding and defense.

Chemical Structure of Proteins: -

Proteins are the linear polymers of amino acids. Proteins can be very long polypeptide chains of hundred to several thousand amino acids. When a large number of amino acids join together, they form polypeptides chains. The amino acids molecules in polypeptide chains are linked by polypeptide bonds. 

[Amino Acid] n → Peptide → Polypeptide → Protein

Peptide Bond: The amino acids of a protein are joined to one another by their respective amino and carboxyl groups i.e. the carboxyl group of one amino acid is joined to the amino group of the next amino acid to form a peptide bond or peptide linkage with the release of one molecule of water.

Fig: - formation of peptide bond

CLASSIFICATION OF PROTEINS: -

Proteins can be classified according to their functions, shape, structures and complexity. On the basis of their conformation the proteins can be classified into two major 

1). Fibrous proteins

2). Globular Proteins 

1). Fibrous proteins: - 

In fibrous proteins polypeptide chains are arranged in a parallel manner along a single axis producing long fibers or sheet like structures. Fibrous proteins Fibrous proteins are insoluble inwater or dilute salt solution. These are the basic structural elements in animal tissues. Keratin of hair and skin, elastin of ligament and collagen of tendons and bone matrix all are examples of fibrous proteins.

2). Globular Proteins: - 

Polypeptide chains are tightly folded into compact spherical or globular shapes. Most of the globular proteins are soluble in water example of globular proteins are all the enzymes, certain hormones, and antibodies etc. 

On the basis of their structure and complexity proteins are classified into three major classes: -

1). Simple proteins 

2). Conjugated or Complex proteins 

3). Derived proteins 

1). Simple proteins: - Proteins which consist solely of amino acid are called simple proteins. These are further classified into the following subclasses: -

Albumins: They are soluble in water and coagulate on heating. They are precipitated by dilute acids and alkalis. Albumins are widely distributed in nature stored as food reserved e.g. egg albumin, serum albumin, legumin (legumes), lactalbumin (milk), leucosin (cereals), gliadin (wheat). 

Protamine: They are basic proteins highly soluble in water, dilute acids and ammonium hydroxide. Protamine are not coagulated by heat. These are simplest of all the naturally occurring. proteins, isolated from mature sperms e.g. Sturine and salmine. 

Histones: These are soluble in water and dilute acids but insoluble in ammonia. They are not coagulated by heat. Histones occur as part of nucleoproteins. 

Scleroproteins: These are also known as albuminoids. Scleroproteins are soluble in water and solutions of neutral salts. They are found exclusively in animals e.g. keratin, collagen, elastin and fibroin.

Globulins: These are insoluble in water but are soluble in dilute neutral salt solution such as NaCl. On heating globulin get coagulated. They are precipitated by half saturated with ammonium sulphate examples of globulins are fibrinogen (blood plasma), egg globulin, myogenic (muscles), legumin (peas), tuberin (potato) etc. 

Glutelins: They are insoluble in water but are soluble in dilute acids and Alkalies, Glutelin get coagulate on heating. These are found exclusively in seeds of cereal grains e.g. glutenin (wheat) and oxyzenin (rice). 

Prolamins: These are insoluble in water but are soluble in dilute alkalies and 50-80% of alcohol. They are not coagulated by heat and found in plants only e.g. hordein (barley), gliadin (wheat) and zein (maize)

2. Conjugated Proteins: -These proteins are composed of not only amino acids but also some nonproteins components. This non-protein substance linked to proteins is called “prosthetic group”. Conjugated proteins are further classified into the following subclasses on the basis of their prosthetic group.

Glycoproteins: In glycoproteins simple proteins are covalently linked with carbohydrate group. The percent of carbohydrate group in different glycoproteins may vary from less than1% in egg albumin to as high as 80% in mucoproteins. Glycoproteins which have very high carbohydrate content are called proteoglycans. Examples of glycoproteins are mucin (saliva), heparin (bile juice), and immunoglobulins (plasma). 

Nucleoproteins: In nucleoproteins protein molecules are combined with nucleic acid. The chromatin material of the nuclei of cells is composed of nucleoproteins e.g. nucleohistones. 

Lipoproteins: Lipoproteins are the proteins in combination with lipids. These are present in the brain, egg, milk and plasma.

Phosphoproteins: Phosphoproteins are formed by the combination of simple proteins with phosphoric acid. Examples of phosphoproteins are vitelline (egg) and casein (milk). 

Metalloproteins: These are proteins linked to some metallic prosthetic group, which also gives colour to the proteins. They are also known as chromoproteins e.g. hemoglobin, hemocyanin, cytochromes and flavoproteins.

3. Derived Proteins: These proteins are derived from some previously existing proteins either by its hydrolysis or by its coagulation. Derived proteins can be divided into two major subclasses.

 Primary derived proteins: - These are denaturized or coagulated proteins. The denaturation is caused by heat, acid or alkali treatment. Their molecular weight is same as the native protein, but they differ in solubility, precipitation and crystallization. Examples are proteins, metaproteins, and coagulated proteins.

Secondary derived proteins:- These are formed by the hydrolysis of complex protein of their peptide linkage. The hydrolysis is caused by the action of digestive enzymes, acids or alkalis. Their molecular weight is different from the native proteins. Examples are proteoses, peptones and peptides. On the basis of their biological functions they are classified into seven major classes: 

i) Structural Proteins: Their function is strengthening or protecting biological structures e.g. keratin, fibroin, collagen, elastin etc. 

ii. Storage and Nutrient Proteins: Their function is to provide nourishment to growing e.g. ovalbumin, giadin, ferritin etc.

iii. Enzymatic Proteins: Their function is to transport molecules in body e.g. hemoglobin,serum albumin, myoglobin etc.

iv. Transport Proteins: Their function is to transport molecules or ions in body e.g. haemoglobin, myoglobin and serum albumin.

v. Regulatory Proteins: Their function is to regulate cellular or metabolic activities e.g. hormones, repressors etc.

vi. Contractile Proteins: Their function is in contractile system e.g. actin, myosin, tubulin, etc.

vii. Defense Proteins: Their function is to provide defense against other organisms e.g. antibodies, ricin etc.

Structural Organization of Proteins: -

Proteins are long polypeptide chains formed by the linkages of several thousand molecules of amino acid with a peptide bond. Proteins can be very long polypeptide chains of 100 to several thousand amino acid residues. There are four different structural level of organization are present in proteins, they are:

1). Primary structure

2). Secondary structure

3). Tertiary structure

4). Quartiary structure

GENERAL PROPERTIES OF PROTEINS: - 

SOLUBILITY 

The solubility of protein varies to the native because proteins are colloids of large-sized molecules these form turbine solution in water. These are also soluble in acid and salt solution while insoluble in alcohol. 

AMPHOTERIC NATURE: -

Like a-acid proteins are amphoteric in nature. They behave as acid alkaline solution and alkaline to acidic solution due to presence of several free- NH2 and COOH groups.

ZWITTERION FORMATION: - 

The protein is either positively or negatively charged molecule and in an electric field migrate either towards cathode or towards anode. They are electrically neutral and do not move towards any pole. 

HYDROLYSIS: -

 The protein undergoes hydrolysis by acid, alkali or hydrolytic enzymes which lead the protein to amino acids. Complete hydrolysis with HCl or H2SO4 and yields free a-acid thin breakdown products. 

DENATURATION 

Under certain conditions there is a disruption of secondary tertiary and quaternary structures of functional protein molecule resulting in the changes of its physical, chemical and biological characteristics. These changes occurring in proteins are collectively called denaturation. During denaturation only primary structure of protein is retained. Various physical and chemical elements such as heat, UV-rays, X-rays, ultrasonic waves, high pressure, acids, alkalis, detergents or certain organic solvents can cause denaturation of proteins. Physical and chemical properties of denatured proteins are different then the native proteins and they lose most of their biological activities, in denatured proteins the solubility is decreased or lost. During denaturation the soluble globular proteins are changed into insoluble fibrous proteins. The process of denaturation also destroys enzyme and hormonal activity and the proteins become biologically inactive. The process of denaturation in some proteins is returned to its native stable confirmation and regains their native structure and biological activity, this process is called renaturation.

METABOLISM OF PROTEINS 

Amino acids are the building blocks of proteins and proteins are the building material in the body. Metabolism of proteins involves both biosynthesis of amino acids as well as breakdown of amino acids. 

BIOSYNTHESIS OF AMINO ACID 

There are 20 standard amino acids known and these can be classified into the group on the basis of their synthesis in human and animals are called the non-essential amino acid whereas the amino acid which cannot be synthesized by the organisms, and they must be obtained through diet are called the essential amino acids. The pathways for the synthesis of these two types of amino acids are quite different. Non essential amino acids can be synthesized by quite simple reaction while synthesis of essential amino acids is quite complex. 

CATABOLISM OF AMINO ACIDS 

Amino acids are not only served as the building blocks of proteins but also serve as source of carbon and nitrogen, when required. The very first step in their catabolism is removal of –NH2 group and formation of corresponding keto-acid. The ammonia, which is liberated, quickly converted to urea and it is incorporated in some other a-acid. Catabolism of a-acid involves the following process:

1. Transamination

2. Deamination

3. Urea formation

4. Decarboxylation

✅Transamination: Russian workers Braunstein and Bychkov had shown the importance of transamination for the first time in 1939. It is the most important process of conversion of amino acid into keto acid. In this process amino group of one amino acid (donor) is transferred to an αketo acid (recipient) resulting in the formation of a new amino acid and a new keto acid. The donor amino acid is converted into a new keto acid and the recipient keto acid is converted into a new amino acid. Transamination is a reversible process and is catalyzed by the enzyme transaminase or amino transferase. Co-enzyme for the reaction is pyridoxal-5’-phosphate, a derivative of vitamin B6 (Pyridoxine). Transamination takes place principally in liver, kidney, heart and brain. Deamination: Deamination is a process in which amino group (-NH2) is removed from the amino acid, which then changes to a α-keto acid. In this process amino group is removed as ammonia. Deamination usually takes place in liver and kidney cells to catabolize excess of amino acids. 

There are two types of deamination:

i. Oxidative deamination

ii. Non oxidative deamination

✅Oxidative Deamination: When deamination process is accompanied by an oxidative reaction, is known as oxidative deamination. This process is catalyzed by a group of flavin containing enzymes known as amino acid oxidases. This is the two step reaction, in the first step the amino acid is dehydrogenated by the flavoprotein of the enzyme. In the next step with addition of H acid is formed. The enzyme amino acid oxidase is auto oxidizable flavoprotein. Reduced flavoprotein is oxidized to form hydrogen peroxide, which then broken up into H catalase.

✅Non oxidative Deamination: There are certain amino acids which can be deaminated non oxidatively. Non oxidative deamination is catalyzed by specific enzymes and NH3 is liberated in this process. One example of non-oxidative deamination is deamination of glutamate by the enzyme glutamate dehydrogenase. This reaction is reversible in which NAD act as coenzyme. Fate of Deaminated Amino Acids: Acids produced from transamination and deamination of amino acids are channeled to several metabolic routes. Some amino acids are deaminated to produce keto acids which are eventually oxidized to CO2 and H2O through acetoacetate and acetyl-co-A.  Aceto acetone is one of the chemical constituents of ‘ketone bodies’ formed in the pathological conditions of urine. 

Thus the amino acid which leads to the formation of acetoacetate during their metabolism are called ketogenic e.g. leucine & lysine Some amino acids are deaminated to produce keto acids which are broken down to pyruvate, α-keto glutamate, succinyl co-A, fumarate or oxaloacetate which can be utilized for the synthesis of glucose or glycogen. This amino acid is called glycogenic or antiketogenic amino acid example of glucogenic amino acids are called glucogenic or antiketogenic amino acids. Examples of glucogenic amino acids are alanine, glycine, serine, aspartate, glutamate, valine, histidine Argene, proline, methionine, cystine and arginine. Some amino acids are precursors of both glucose and ketone bodies are known as glucogenic and ketogenic amino acids. Examples are phenylalanine, tyrosine, isoleucine, threonine and tryptophan. Fate of Ammonia: Ammonia released during deamination is either converted into ammonium salt or into urea.

Formation of ammonium salts: -Ammonium ions (NH4+) are formed from some of the ammonia released by deamination of amino acids. These ammonium ions are excreted out from the body in the form of ammonium salts.

Formation of Urea (Urea cycle): When production of ammonia exceeds beyond a certain level it become toxic. Excess of ammonia produced during the deamination of amino acids is converted to less toxic substance, urea, before been excreted in the urine. Formation of urea is a cyclic process and the cycle is known as urea cycle. This cycle was first outlined by Hans Krebs and Kurt Henslie in 1932; hence it is also known as Kreb’s Hanseleit cycle. The chief site for urine formation is liver and after its formation urea passes into the blood Strem and form blood to kidneys s and finally excreted into the urine. Urea synthesis takes place in five steps. Each step is catalyzed by a specific enzyme. Out of these five enzymatic reactions, two take place in the mitochondria and three take place in the cytoplasm. This cycle is also known as ornithine cycle as it involves conversion of amino acid ornithine to citrulline though glutamic acid which is derived from aspartic acid by transamination and/or form α- ketoglutaric acid and ammonia.

Decarboxylation: Decarboxylation is the process in which CO2 is removed from the carboxyl group of an amino acid resulting the formation of an amine. Enzyme aminoacidic decarboxylases catalase these reactions which require pyridoxal phosphate as coenzyme. For example, histidine is decarboxylated to histamine by histidine decarboxylase and 3,4- dihydroxyphenylalanine is decarboxylated to dopamine. These types of amines are called, biogenic amines. Many of these amines have strong pharmacological effects and others are important as precursors of hormones or as co-enzymes.

SOURCES OF PROTEINS 

Proteins are widely distributed in plants and animals. Common sources of proteins are milk, yogurt, cheese, fishes, beans, nuts, green peas, meat, eggs, lentils, soy products, quinoa and sea foods.

BIOLOGICAL SIGNIFICANCE OF PROTEINS 

Proteins are the most significant macromolecules in living beings because of the following physiological roles performed by them in all biological processes:

1. Proteins which are involved in the formation and maintenance of various cellular structures are called structural proteins. These proteins form an important part of all membranes and membrane bound organelles of the cell. The cell wall and primary fibrous of the cell have structural proteins e.g. Collagen is the most abundant fibrous protein found in animals forming a major part of the skin, cartilage, ligament, tendons and bones. Keratin is another animal protein involved in the formation of scales, hair, feather, horns, hoofs, fur wool, nails and claws.

2. Capacity of motion and flexibility in the organisms is due to the presence of certain proteins called contractile proteins e.g. Muscle proteins- actin and myosin.

3. Proteins acts as enzymes or biocatalysts and catalyzes a variety of chemical reactions in the living organisms. Almost all the enzymes are protein in nature.

4. Some proteins bind and transport specific types of molecules via blood e.g. hemoglobin is important protein, transports oxygen from lungs to cell tissues. Myoglobin binds and transports oxygen in the muscles. Certain membrane proteins transport ions and small molecules across the cell membrane.

5. Some proteins are stored as reserve food such as albumin in egg and glutelin in rice. In the liver ferritin stores iron.

6. A few proteins functions as hormone e.g. insulin.

7. Proteins also play important role in the immune system of vertebrates. Antibodies are immunoglobulins which combine and neutralize the antigen entering the body.

8. Proteins also take part in blood coagulation e.g. thrombin and fibrinogen.

DEFICIENCY DISEASES OF PROTEINS 

Protein deficiency can lead to weak muscle tone, thin and brittle hair, edema or swelling, skin lesions, fatigue, stunted growth and cognitive development as well as mental health in children. Following diseases can occur due to protein deficiency: 

Marasmus: It affects infants and very young children, often resulting in weight loss and dehydration. People with marasmus appear bony with little muscle tissue.

Kwashiorkor: It usually affects older children. People with Kwashiorkor appear swollen stomach due to fluid retention.

Cachexia: It is a condition that involves protein deficiency, depletion of skeletal muscle and an increased rate of protein degradation. It causes weight loss and mortality and is associated with cancer, AIDS, heart disease and chronic kidney failure.

Reproductive health; problems and strategies| Population explosion| Birth control methods|

  Reproductive Health: Problems and Strategies 

Reproductive Health simply refers to healthy reproductive organs with normal functions. According to the World Health Organization (WHO), reproductive health means a total well-being in all aspects of reproduction, i.e., physical, emotional, behavioral and social. The improved reproductive health of society requires following factors. 

✔ Better awareness about sex-related matters. 

✔ Increased number of medically assisted deliveries and better postnatal care so, as to decrease maternal and infant mortality rates. 

✔ Increased number of couples with small families. 

✔ Better detection and cure of STDs (Sexually Transmitted Diseases). 

✔ Overall increased medical facilities for all sex-related problems. 

✒Awareness of Reproductive Health: -

Some of the measures taken for the awareness of reproductive health are as follows: -

(i) The family planning programmes were initiated in India in 1951 and were periodically assessed over the past decades. The programmes were improved and covered reproduction-related areas under the popular name Reproductive and Child Healthcare (RCH) programmes. It was launched in 1997. Major tasks of RCH programme are: -

✅Creating awareness among the people about reproduction related aspects. 

✅ Providing facilities and support for building up a reproductively healthy society. Governmental and non-governmental agencies have taken various important steps to create awareness among people about reproduction-related aspects. 

(ii) In schools, introducing sex education is a good step to provide right information to adolescents to discourage them from believing in myths and misconceptions about sex-related issues. Adolescents should be informed about reproductive organs, adolescence and related changes, safe and hygienic sexual practices, sex abuse, STDs, AIDS, etc.

 (iii) Married couple or those in marriageable age group should be educated about available birth control options, care of pregnant mothers, postnatal care of the mother and child, importance of breast feeding, equal opportunities for the male and female child, etc. This will lead to the formation of socially conscious healthy families of desired size. 

(iv) Successful implementation of action plans like providing medical assistance and care to reproduction-related problems, pregnancy, delivery, STDs, abortions, contraception, menstrual problems, infertility, etc. need strong support and infrastructural facilities.

(v) Statutory ban on amniocentesis It is a prenatal diagnostic technique based on chromosomal pattern in which a sample of amniotic fluid is taken from the uterus of a pregnant woman to detect the early development of foetus. The benefits of amniocentesis include the diagnosis of chromosomal abnormalities and developmental disorders of it foetus. However, is being misused for sex-determination of foetus that leads to female foeticides. Therefore, statutory ban on for amniocentesis sex-determination keeps check on female foeticides. 

Population Explosion: -

The tremendous increase in the size and growth rate of population is called population explosion. It occurs due to increased health better living conditions.

(i) Reasons of population explosion include 

✅ Decreased death rate. 

✅ Declined Maternal Mortality Ratee (MMR). 

✅ Decreased Infant Mortality Rate (IMR). 

✅Increase in the number of people in reproductive age. 

(ii) According to the 2001 census report, the population growth rate was around 1.7%, i.e. 17/1000/year. By this rate, our population could double in 33 years. 

Methods to prevent population explosion include 

✔ Raising the marriageable age now, it is 18 years for females and 21 years for males. 

✔ Couples with small families should be given some incentives. 

✔ Birth control is an important step to control the population growth by motivating smaller families by using contraceptive methods. 

Birth Control (Contraception) Methods: - 

Contraceptive methods are ideal if they are user friendly, easily available, effective, reversible with no side effects and non-interferring with the sexual drive, desire and the sexual act. There are several methods of birth control that can be categorised as follows: - 

Natural Methods: -

Natural method of birth control involves avoiding ances of sperm and ovum meeting. It can be achieved by 

•  Periodic abstinence in which couples avoid coitus from day 10-17 (fertile period) of the menstrual cycle. In this period, ovulation 1s expected to occur and chances of fertilization are very high. This method is also called rhythm method. 
•  Coitus interruptus is also called 'rejected Sexual intercourse' or 'pull-out'/withdrawl method. In this method, the penis is withdrawn from the vagina just before ejaculation, so that semen is not deposited in the vagina.

• Lactational amenorrhea is the absence of menstruation during the period of intense lactation following parturition. As ovulation does not occur in this period, the chances of conception are nil. This method is reliable for a maximum period of 6 months after delivery. Main advantage of these methods is that, they do not cause any type of side effect. The main disadvantage is that, these methods are not 100% reliable, as these depend on chance. 

Barrier Methods: -

These methods are based on the prevention of ovum and sperm from physically meeting with the help of barriers. Barriers may be mechanical or chemical and uscd by both males and females 

(i) Mechanical Barriers: -

✅Condoms:-

 They are made of thin rubber or latex sheath to cover the penis in male or vagina and cervix in females (femidom) They prevent meeting of sperm and ova. Condoms provide protection from sexually transmitted discases. They are disposable and can be self-inserted and thereby gives privacy to the user. 

✅Diaphragms, Cervical Caps and Vaults: - They are made up of rubber that are inserted into the female reproductive tract to cover the cervix during coitus. They are reusable. 

(ii) Chemical Barriers: -

They include spermicidal creams, jellies and foams. They are usually used along with the barriers to increase their contraceptive efficiency.

Intra Uterine Devices (IUDS): - 

These devices are introduced in the uterus through vagina by doctors or expert nurses. These are of following types: -

✅Non-medicated IUDs, e.g. Lippes loop. 

✅ Copper-releasing IUDs, e g. Cu-T, Cu-7 and multiload 375. 

✅ Hormone-releasing IUDs, e.g. progestasert, LNG-20.

IUDs prevent contraception in the following ways: -

✅ Increase phagocytosis of sperms within the uterus. 

✅ Some IUDs suppress sperm motility and fertilizing ability of sperm by releasing copper ions. 

✅The hormone releasing IUDs make uterus unsuitable for implantation and make the cervix hostile to sperms. IUDs are ideal Contraceptives for females who want to delay pregnancy. It is one of the most widely accepted contraception method in India.

Oral Contraceptives: -

These are hormonal preparations in the form of pills. Their major fecatures include 

(i) Pills are of two types-combined pills and mini pills. Combined pills (Mala-D and Mala-N) contain synthetic progesterone and oestrogen whereas mini pills contain progestin (progesterone like synthetic hormone) only. 

(ii) Oral pills inhibit ovulation and modify the quality of cervical mucus to prevent/retard the entry of sperms. They also modify uterine endometrium by making it unsuitable for implantation. 

(iii) Oral pills have to be taken daily for a period of 21 days starting within the first five days of menstrual cycle. 

(iv) Saheli an oral contraceptive pill developed by scientists at Central Drug Research Institute (CDRI), Lucknow, contains a non-steroid called centchroman. It is a once-a-week pill, with very few side effects and high contraceptive value. 

Implants or injections: -

These are effective for longer period, although their mode of action is similar to thal of oral contraceptives. Progesterone alone or in combination with oestrogen are used by females as injections (Depo Provera) or implants under the skin. 

Emergency Contraceptives: -

It includes administration of high dose of progesterone or progestogen-Oestrogen Combinations within 72 hours of coitus. It has been found to be very effective to avoid possible pregnancy due to unprotected intercourse.

Sterilisation or Surgical Methods: -

Sterilisation methods are used by male/female partner as a terminal/ permanent/stable method to prevent any more pregnancies. These methods block the transport of gametes and prevent Contraception. There are of following two types 

(i) Vasectomy is applied in case of males. In this method, a small portion of vas deferens is removed or tied up through an incision on the scrotum to prevent the passage of sperms.

 

(ii) Tubectomy is applied in case of females, where a small part of Fallopian tube is removed or tied up through a small incision in the abdomen or through vagina to prevent the passage of ova. Both of these methods are highly effective. but poorly reversible.