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Actin filaments form a meshwork just underlying the plasma membrane of cells and are referred to as cell cortex. The additional information is represented in the form of diagrams, tables and flows charts. The cytoskeleton consists of three primary protein filaments: There is a wide variation in the protein shape. It consists of steroid nucleus namely phenanthrene containing carbon atoms Figure 3.

Starch is composed of two constituents viz. Homopolysaccharides Homoglycans: When a polysaccharide is made up of several units of one and the same type of monosaccharide unit only. Heteropolysaccharides Heteroglycans: They contain two or more different types of monosaccharide units or their derivatives. The anomeric carbon of both glucose and fructose are involved in the glycosidic bond Figure 2.

Polysaccharides are colloidal in size. Sucrose is hydrolyzed to fructose and glucose by an enzyme sucrase which is also called invertase. The structure of glycogen is similar to that of amylopectin. It is formed by plant but not by human beings. Glycogen Animal Starch Glycogen is the major storage form of carbohydrate glucose in animals. Structure of amylose. All dextrins have few free aldehyde groups and can show mild reducing property.

Polysaccharides are subclassified in two groups Table 2. Sucrose is therefore. Diagrammatic representation of glycogen molecule Cellulose Cellulose is the chief constituent of cell wall of plants.

Structure of amylopectin cannot be digested and absorbed and has no food value unlike starch. Structure of cellulose. It occurs in the tubers of some plants. Has a role in compressibility of cartilage in weight bearing Keratan sulfate N-Acetyl-glucosamine-Galactose no uronic acid Transparency of cornea Dermatan sulfate N-Acetyl-galactosamine-L-lduronic acid Transparency of cornea and maintains the overall shape of the eye Heparin Glucosamine-Glucuronic acid or Iduronic acid Serves as an anticoagulant.

Clinical importance of Inulin Inulin has clinical importance as it is used in the studies of glomerular filtration rates kidney function test.

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Bottle brush structure of proteoglycan monomer Table 2. It increases bulk of stool. They lubricate joints both at the surface of cartilage and in synovial fluid. Glycoproteins contain much shorter carbohydrate chain than proteoglycans.

Most proteins that are secreted. The viscous lubricating properties of mucous secretions are also due to the presence of glycosaminoglycans. GAGs carry sulfate and carboxyl groups which give them a negative charge and have special ability to bind large amounts of water. The distinction between glycoproteins and proteoglycans may be based on the amount of carbohydrate.

The amount of carbohydrates in proteoglycans is usually much greater than is found in a glycoprotein and may comprise upto 95 percent of its weight.

With the exception of hyaluronic acid. Many integral membrane proteins are glycoproteins. Glycoproteins are proteins to which oligosaccharides are covalently attached to their polypeptide chain. Occurrence of GAGs Glycosaminoglycans are found in the: All the following are composed exclusively of: Glycosaminoglycans are: Many cell surface proteins and extracellular proteins are glycoproteins.

Glycoproteins also serve as transport molecules. Which of the following statements is true for fructose? D-galactose and D-glucose are: The sugar residues of glycogen are: Polysaccharides glycans contain many monosaccharide units in glycosidic linkage. Sugars with free. Proteoglycans and glycosaminoglycans contains sugar derivatives such as amino sugar. Disaccharides consists of two monosaccharides joined by the glycosidic bond. Inulin is: Some function as storage forms of carbohydrates.

Carbohydrates are classified as monosaccharides. Which of the following GAGs does not contain uronic acid? Which of the following glycosaminoglycans is unsulfated? Glycoproteins are proteins attached to oligosaccharides. Which of the following carbohydrate is dietary fiber? This chapter introduces the chemistry and functions of lipids. Neutral fats or triacylglycerol or triglycerides 2. The fat we eat are mostly triglycerides.

Lipids include fats. Classification of Lipids There are many different methods of classifying lipids. These compounds have no importance as far as human metabolism is concerned. Derived lipids. They are esters of fatty acids with alcohol esters and are utilizable by the living organism.

A fat in liquid state is called an oil. The most commonly used classification of lipids is modified from Bloor as follows: Depending on the type of alcohols. Lipid Bilayer. Simple Lipids These are esters of fatty acids with various alcohols. Because they are uncharged.

Lipids are a heterogenous group of water insoluble hydrophobic organic molecules. Neutral fats or triacylglycerol or triglycerides These are esters of fatty acids with alcohol glycerol.

Waxes True waxes These are esters of fatty acids with higher molecular weight monohydric long chain alcohols. Complex or compound lipids 3. Sphingophospholipids The alcohol present is sphingosine. These are subclassified according to the type of prosthetic group present in the lipid as follows: Lipoproteins Lipoproteins are formed by combination of lipid with a prosthetic group protein.

They do not contain phosphate group. Glycerophospholipids The alcohol present is glycerol. They act as a solvent for the transport of fat soluble vitamins. For example: Complex or Compound Lipids These are esters of fatty acids.

Phospholipids may be classified on the basis of the type of alcohol present in them as: Functions of Lipids Lipids serve as: The fats and oils are used almost universally as stored forms of energy in living organisms.

Glycolipids Lipids containing fatty acid. Phospholipids Lipids containing. E and K. Derived Lipids Derived lipids include the products obtained after the hydrolysis of simple and compound lipids which possess the characteristics of lipids.

Phospholipids 2. They also have nitrogen containing bases and other substituents. Examples of glycerophospholipids are: The fatty acids are amphipathic in nature. Lipids are major structural components of membranes. These sugar containing sphingolipids are also called glycosphingolipids. Glycolipids 3. Other waxes These are esters of fatty acid with alcohol. Branched chain fatty acids 3. Unsaturated fatty acids These contain double bonds in their hydrocarbon chains.

Saturated fatty acids There is no double bond in the hydrocarbon chain of these fatty acids. Saturated fatty acids ii. Straight chain fatty acids 2. Classification of Fatty Acids Fatty acids are classified into four major classes Figure 3. Polyenoic or polyunsaturated fatty acid. Cyclic fatty acids. Odd carbon acids carry odd number of carbons. Monoenoic or monounsaturated fatty acid b. Even carbon acids carry even number of carbons.

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These are subclassified according to the number of double bonds present in the structure as follows: Straight Chain Fatty Acids Fatty acids. Substituted fatty acids 4. Unsaturated fatty acids. Saturated fatty acids are subclassified into two classes: Functions of Fatty Acids Fatty acids have three major physiological functions. Fatty acid derivatives serve as hormones.

Branched Chain Fatty Acids These are less abundant than straight chain acids in animals and plants. Substituted Fatty Acids In substituted fatty acids one or more hydrogen atoms have been replaced by another group. Figure 3. They serve as building blocks of phospholipids and glycolipids. Numbering of fatty acid carbon. Cyclic Fatty Acids Fatty acids bearing cyclic groups are present in some bacteria and seed lipids.

Linolenic acid present in poppyseed oil. These amphipathic molecules are important components of biological membranes. Fatty acids serve as a major fuel for most cells.

They are polyunsaturated fatty acids.

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Representation of double bonds of unsaturated fatty acid. This method is widely used by nutritionists. Arachidonic acid. And thus. Arachidonic acid can be synthesized from linoleic acid. Humans lack the enzymes to introduce double bonds at carbon atoms beyond C9 in the fatty acid chain. Linoleic acid C: Linolenic acid C: These fatty acids are important constituents of phospholipids in cell membrane and help to maintain the structural integrity of the membrane. Antiatherogenic Effect Essential fatty acids increase esterification and excretion of cholesterol.

Synthesis of Eicosanoids Linoleic acid and linolenic acid supplied by the diet are the precursors for the synthesis of a variety of other unsaturated fatty acids. Since iodine is taken up by the double bonds.

Peroxidation Peroxidation auto-oxidation of lipids exposed to oxygen is responsible not only for deterioration of foods rancidity but also for damage to tissues in vivo. Rancidity may be due to hydrolysis or oxidation of fat. The products are glycerol and the alkali salts of the fatty acids. To control and reduce peroxidation. The action of lipase brings about partial hydrolysis of glycerides of fat.

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Many natural vegetable fats and oils may contain antioxidants like vitamin E which prevent onset of rancidity. Iodine number is important in the identification of the fat or oil as well as is used for identification of adulteration of oils. Saponification Number Figure 3. This value is high in fats containing a short chain fatty acids. Impaired lipid transport and fatty liver may occur due to deficiency of EFAs.

It is commercially valuable as a method of converting these liquid fats. Naturally occurring antioxidants It is defined as. Rancidity The unpleasant odor and taste. EFAs deficiency decreases efficiency of biological oxidation.

Naturally occurring fats. It is inversely proportional to the molecular weight of fat. Lipid peroxidation is a chain reaction generating free radicals that initiate further peroxidation. Acid hydrolysis of a fat yields the free fatty acids and glycerol. Glycerophospholipids or Phosphoglycerides Figure 3.

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The presence of the unsaturated fatty acid s in triacylglycerol decreases the melting temperature of the lipid and remains in liquid form oil. Refined oil should not contain free fatty acids.

Phospholipids are the major lipid constituents of cell membranes. The acid number indicates the degree of rancidity of the given fat. Sphingophospholipids that contain sphingosine as the alcohol. The presence of free fatty acids in any oil indicates that it is not pure. Like fatty acids.

Triacylglycerol consists of three fatty acids. Triacylglycerols are highly concentrated storage form of metabolic energy. That on carbon 2 is usually unsaturated and that on carbon 3 can be either of the two. Triacylglycerols containing only saturated fatty acids. Acid number is directly proportional to the rancidity. Glycerophospholipids or phosphoglycerides. Reichert Meissl Number The number of ml of 0.

The edibility of a fat is inversely proportional to the acid number. Diagrammatic representation of amphipathic phospholipid Classification of Phospholipids There are two classes of phospholipids Figure 3. It is less than one for other edible oils. Vegetable oils such as corn and olive oil are composed largely of triacylglycerols with unsaturated fatty acids and thus are liquids at room temperature. The stereospecific numbering sn of the glycerol carbon atom is shown in Figure 3.

The admixture of certain fats may be used to prepare synthetic butter which may simulate butter in most of the constants except RM value and hence. The fatty acid on carbon 1 is usually saturated.

It reduces surface tension in the alveoli. These are most abundant phospholipids of the cell membrane having both structural and metabolic functions. Phosphatidic acid is a key intermediate in the biosynthesis of other glycerophospholipids. Different types of glycerophospholipids are discussed below.

Classification of phospholipids is necessary for normal lung function. The C3 hydroxyl group of the glycerol is esterified to phosphoric acid and resulting compound called. In glycerophospholipid.

Phosphatidylserine It contains the amino acid serine rather than ethanolamine and is found in most tissues Figure 3. Phosphatidylethanolamines iii. The most common of these are lysophosphatidylcholine lysolecithin Figure 3.

Structure of different phospholipids There are three major classes of plasmalogens: Phosphatidylcholines ii. Thromboplastin coagulation factor III. Globosides 4. Classification of Glycolipids Four classes of glycolipids have been distinguished: Phospholipids are important constituents of lipoproteins.

Lecithin represents a storage form of lipotropic factor choline. Phospholipids are of importance in insulating the nerve impulse like the plastic or rubber covering around an electric wire from the surrounding structures. Glycolipids consist of alcohol sphingosine. They regulate permeability of membranes as well as activation of some membrane bound enzymes. Lipotropic factor is the component that prevents fatty liver.

Phosphatidylinositol acts as a second messenger for the activity of certain hormones. Phospholipids act as a lipotropic factor. Cerebrosides 2. Plasmalogens platelet activating factor involved in platelet aggregation and degranulation. In mitochondria. Glycolipids are widely distributed in every tissue of the body.

The amino group of sphingosine is esterified by a fatty acid and one or more sugar units are attached to the hydroxyl group of sphingosine. Phospholipid lecithin acts as lung surfactant. Sulfatides 3. The steroid nucleus. Glycolipids are antigenic and they have been identified as a source of blood group antigens. B and C.

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They play a role in the regulation of cellular interactions. M represents mono which indicate presence of one residue of NANA and subscript number assigned on the basis of chromatographic migration of ganglioside. Glycolipids serve as cell surface receptors for certain hormones and a number of drugs. It consists of steroid nucleus namely phenanthrene containing carbon atoms Figure 3.

Sterols are a class of steroids containing hydroxyl group. G represents Ganglioside. They also serve as receptors for cholera and tetanus toxins. The simplest ganglioside found in tissues is GM3. It consists of methyl side chains at position C10 and C13 which are shown as single bonds.

These glycolipids are important constituents of the RBC-membrane and are the determinants of the A. Cholesterol serves as the precursor for a variety of biologically important products. The density of these lipoproteins is inversely proportional to triacylglycerol content. Very low density lipoproteins VLDL 3.

High density lipoprotein HDL. Mineralocorticoids iv. Cholesterol is widely distributed in all the cells of the body but particularly in nervous tissue. Lipoproteins consist of a lipid core containing nonpolar triacylglycerol and cholesterol ester surrounded by a single layer of amphipathic Classes of Lipoproteins Lipoproteins have been categorized into four major classes according to their physical and chemical properties Table 3.

It occurs in animal fats but not in the plant fats. Cholesterol is the predominant lipid in LDL. As the density increases.

Progesterones ii. Vitamin D: It is derived from cholesterol and is essential in calcium and phosphate metabolism. Androgens male sex hormones vi.

Steroid hormones: Cholesterol is the precursor of the five steroid hormones. Most of the cholesterol in the body exists as a cholesterol ester. Chylomicrons 2. Bile acids: Bile acids. Estrogen female sex hormones. Glucocorticoids iii. Low density lipoprotein LDL 4. There are four major types of apolipoproteins designated by letters A. The protein components are referred to as an apoprotein or apolipoprotein.

Structure of lipoprotein where. C and E with subgroups given in Roman numerals I. Prostaglandins are a group of carbon compounds derived from arachidonic acid Figure 3. In addition to cyclopentane ring. Prostanoic acid does not occur naturally but is regarded as the parent compound of the prostaglandins and thromboxanes for the purpose of classification and carbon numbering.

A polyunsaturated fatty acid containing carbon atoms from which they take their general name Greek: They derive their name from the tissue in which they were first recognized the prostate gland but they are now known to be present in almost all tissues.

Diagrammatic representation of lipoprotein with increasing densities Site of Synthesis and Functions of Lipoproteins The site of synthesis of the four main lipoproteins and their functions are summarized in Table 3. Table 3. Some of these are: Prostaglandins have an effect on platelet aggregation. As cAMP mediates the action of many hormones.

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PGE2 are involved in relaxation of bronchial smooth muscle. Prostaglandins elevate body temperature producing fever and cause inflammation. H and I depending on the substituents on the cyclopentane ring. It can lower systemic arterial pressure through their vasodilator effect. PGE2 decrease blood pressure. PGE2 suppress gastric secretion. The structure of arachidonic acid. Because of this effect.

These are PGE1. PGE2 promote aggregation and are thus. PGs are involved in inflammatory response causing pain. They have six membered oxane ring Figure 3. Platelet aggregation initiates thrombus formation at sites of vascular injury. Different capital letters are used to designate different substituents of the ring like prostaglandins. Thromboxanes Thromboxanes were first isolated from blood platelets.

In these structures. It has a hydrophilic or polar head phosphate group attached to choline. Formation of micelle. Overproduction of LT causes asthmatic attacks. In aqueous systems the polar phospholipid spontaneously disperse to form micelles. In the laboratory. LTD4 induce contraction of muscle of the lung and constrict pulmonary airways.

Vesicles formed by these methods are nearly spherical in shape Figure 3. Liposomes can be used to study membrane permeability or to deliver drugs to cells. In aqueous solutions. The precursor for vitamin D is: Glycerol is the backbone of: All of the following statements about lipids are true. Which ring of the cholesterol molecule contains a double bond? Lysophospholipids also have detergent like action. The lipoprotein particles that have the highest concentration of triacylglycerol are: Which of the following lipids is deficient in infants with respiratory distress syndrome?

All of the following are sphingolipids. Which of the following carbohydrates distinguishes a ganglioside from a globoside? Triacylglycerols contain three fatty acid molecules esterified to the three hydroxyl groups of the glycerol and are storage fats. The proteins of the lipoprotein are referred to as apoprotein or apolipoprotein. All of the following statements about prostaglandins are true.

Lipoproteins are macromolecular complexes that transport insoluble lipids in the blood. Methylated form of phosphatidyl ethanolamine is known as: Detergents are amphipathic molecules. The polar lipids phospholipids. Some lipids serve as structural component of membrane and others as storage form of fuel.

The bile acids and bile salts are powerful naturally occurring detergents which emulsify fats in the digestive tract. Liposomes are artificially formed phospholipid vesicles. All of the following statements are true for phosphoglycerides. Cerebrosides and gangliosides are glycolipids which contain various sugar components. Which of the following is the major storage and transport form of fatty acids? Which of the following phospholipids has an antigenic activity? Which of the following statements about cholesterol is true?

Which of the following glycolipids is known to be the receptor in human intestine for cholera toxin? Structure of the side chain of the amino acids 3. Proteins are linear chains of amino acids that are linked together by covalent. All the 20 amino acids found in proteins Table 4. Each protein has specific and unique sequence of amino acids that defines both its three-dimensional structure and its biologic function. The 20 amino acids of proteins are often referred to as the standard or primary or normal amino acids.

They are responsible for almost every function that occurs in the body. All the amino acids found in proteins are exclusively of the L-configuration. Nature or polarity of the side chain of the amino acids. Chemical nature of the amino acid in the solution 2. As the name indicates. Nutritional requirement of amino acids 4.

Metabolic product of amino acids 5. Figure 4. Amino acids differ from each other in their side chains or R-groups. The Acidic amino acids iii. Neutral amino acids The amino acids which are neutral in solution and are monoamino-monocarboxylic acids i. Basic amino acids. Neutral amino acids ii. Sulfur containing amino acids 4. Structure of proline Nutritional Classification of Amino Acids On the basis of nutritional requirement.

Nonessential or dispensable amino acids. Hydroxy amino acids Amino acids having hydroxy group in the side chain. Imino acids or heterocyclic amino acids. Dicarboxylic acid and their amides Amino acids having carboxylic group in their side chain. Diamino acids 6. Nonessential amino acids Nonessential amino acids can be synthesized in human body and are not required in diet. Essential or indispensable amino acids ii. A deficiency of an essential amino acid impairs protein synthesis and leads to a negative nitrogen balance nitrogen excretion exceeds nitrogen intake.

Arginine and histidine become essential in diet during periods of rapid growth as in childhood and pregnancy. Essential amino acids also refer Chapter 11 Essential amino acids cannot be synthesized by the body and must.

Sulfur containing amino acids Amino acids having sulfur in the side chain. Ten amino acids. The mnemonics often used by students are PVT. Hydroxy amino acids 3. Diamino acids Amino acids having amino group -NH2 in the side chain. Aromatic amino acids 7. Among the ten essential amino acids. Aromatic amino acids Amino acids containing aromatic ring in the side chain. Dicarboxylic acid and their amides 5.

Aliphatic amino acids Amino acids having aliphatic side chain. HALL or L. Aliphatic amino acids 2. Hydrophilic or polar amino acids ii. Classification of amino acids based on polarity. Lysine aspargine. Detoxification reactions: Amino acids are joined to each other by peptide bonds to form proteins and peptides.

Formation of glucose: Glucogenic amino acids are converted to glucose in the body. Transport and storage form of ammonia: Amino acid glutamine plays an important role in transport and storage of amino nitrogen in the form of ammonia. Formation of biologically important compounds: Specific amino acids can give rise to specific biologically important compounds in the body Table 4.

Enzyme activity: The thiol -SH group of cysteine has an important role in certain enzyme activity. Glucogenic amino acids: Those which can be converted into glucose. Hydrophobic or nonpolar amino acids. These amino acids are formed by the modification of one of the Figure 4. Four amino acids isoleucine. Metabolic classification of amino acids Glucogenic Ketogenic Glycine.

As a buffer: Both free amino acids and some amino acids present in protein can potentially act as buffer. Metabolic Classification of Amino Acids On the basis of their catabolic end products. Both glucogenic and ketogenic: Those which can be converted to both glucose and ketone bodies.

Ketogenic amino acids: Those which can be converted to ketone bodies. Two amino acids leucine and lysine are exclusively ketogenic. Fourteen out of the twenty standard amino acids are glucogenic amino acids Table 4. Leucine cysteine. Table 4. Due to ionizing property of amino acids. Biologically important compounds formed by amino acids Amino acid Biologically important compound Tyrosine Hormone. Optical Properties All naturally occurring amino acids are optically active except glycine which is optically inactive.

Selenocysteine has a structure similar to cysteine. At pH 7. The following modified amino acids are of particular significance. Formation of disulfide bond of cystine Hydroxyproline and Hydroxylysine The hydroxylation of selected lysine and proline residues is found primarily in the formation of collagen of connective tissue.

Cystine Cystine is formed by linkage of two cysteine side chains through a disulfide bond Figure 4. Ionization of Amino Acids Figure 4. Desmosine and Isodesmosine These two amino acids are formed by the oxidation and crosslinking of four lysine side chains. The amino acid selenocysteine is present at the active site of several human enzymes that includes: These are found in connective tissue protein. This modified amino acid is found in many proteins.

The net charge of an amino acid depends upon the pH of the medium. In addition. D and L forms of amino acids Thus. Amphoteric properties of amino acids and formation of zwitter ion at isoelectric pH Substances having a two-way property are called amphoteric or ampholytes Greek word ampho means both. Ionization of amino acid Figure 4. As amino acids have both acidic and basic groups.

Isoelectric pH PI The pH at which amino acid bears no net charge zwitter ion and therefore does not move in an electric field is called isoelectric pH PI. Ionic forms of amino acid in acidic.

Among the 20 standard amino acids. A few of them are given below. Two amino acid molecules can be covalently joined through a peptide bond. Glutathione is found in all mammalian cells except the neurons. When many amino acids are joined. Because the side chain of histidine has a pKa of 6.

There are many naturally occurring small polypeptides some of which have important biological activities and are called biologically important peptides. All other amino acids have pKa value. Cells with lowered level of reduced glutathione are more susceptible to hemolysis. Maximum buffer capacity occurs at pH equal to the pKa. In oxidized form. Glutathione Peroxidase Figure 4. Proteins are polypeptides with thousands of amino acids. The sulfhydryl -SH- is the functional group primarily responsible for the properties of glutathione.

It stimulates the release of hormone thyrotropin. This is a 9-amino acid residue hormone secreted by posterior pituitary and stimulates uterine contractions. In a functional classification, they are grouped according to their biological role.

Some functions that proteins serve and examples of specific functional proteins are as follows:. Vasopressin This is a 9-amino acid residue hormone secreted by posterior pituitary and it increases blood pressure and has an antidiuretic action. Gastrin This is a local hormone produced by stomach. It stimulates the production of gastric juice. Angiotensin Angiotensin II is a vasoconstrictor and elevates the arterial pressure and also promotes the synthesis of a steroid hormone called aldosterone that promotes sodium retention.

Bradykinin It contains, 9-amino acid residue. It is a powerful vasodilator and causes contraction of smooth muscle and is mainly responsible for causing intense peripheral and visceral pain by stimulating the pain receptors.

Catalytic Proteins or Enzymes These proteins act as enzymes, e. Transport Proteins These proteins are involved in the process of transportation, e. Storage Proteins Many proteins serve as storage form, e. A pancreatic hormone contains two polypeptide chains: Insulin regulates the glucose concentration in blood. Some proteins have the ability to contract and function in the contractile system of skeletal muscle, e.

Many proteins serve as supporting framework of cells to give biological structure, strength or protection, e. Proteins are linear chains of amino acids that are linked together by covalent, peptide bonds.

Many proteins involved in defence mechanism against invasion of foreign substances such as viruses, bacteria and cells. Examples of defence proteins are: Classification of Proteins Proteins have been classified in several ways. They are most conveniently classified on the basis of their: Function 2. Physical and chemical properties. Many hormones, e. Classification of Proteins Based on Physical and Chemical Properties of Protein According to the joint committee of the American Society of Biological Chemists and American Physiological Society, proteins are classified into three main groups as follows: Simple proteins 2.

Conjugated proteins 3. Derived proteins. Simple Proteins Simple proteins are defined as those proteins that upon hydrolysis, yield only amino acids or their derivatives. They are subclassified according to their solubility and heat coagulability as follows: Albumins The albumins are soluble in water, coagulated by heat. It is deficient in glycine, e. Globulins The globulins are insoluble in water, but they are soluble in dilute neutral salt solution and are heat coagulable, e.

Glutelins The glutelins are soluble in dilute acids and alkalies but they are insoluble in neutral solvents. They are plant proteins, e. The prolamins are rich in proline but are deficient in lysine. Histones The histones are soluble in water, but are not coagulated by heat. Histones are basic proteins as they are rich in. The histones, being basic, usually occur in tissues in salt combinations with acidic substances, such as nucleic acids RNA and DNA , e.

Protamines They are strongly basic and rich in basic amino acid arginine. The protamines are soluble in water but are not heat coagulable. Like histones, they occur in tissues with nuleic acids, e. Scleroproteins fibrous proteins Fibrous proteins are also called sclero proteins.

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They are insoluble, in all common solvents like water, neutral salt solution, organic solvents, dilute acid and alkali high molecular weight fibers. Examples of sclero proteins are: Conjugated Proteins Conjugated proteins are composed of simple protein combined with some non-protein substance. The nonprotein group is referred to as the prosthetic additional group.

Following are the examples of conjugated proteins: Nucleoproteins The nucleoproteins are composed of simple basic proteins histones or protamines with nucleic acids RNA and DNA as the prosthetic groups. They are proteins of cell nuclei, e. Glycoproteins and proteoglycans or mucoproteins These consist of simple protein and carbohydrate as a prosthetic group. Chromoproteins Chromoproteins are composed of simple proteins with a colored prosthetic group, e.

In all these chromo proteins, prosthetic group is heme. Phosphoproteins The phosphoproteins are formed by a combination of protein with prosthetic group phosphoric acid, e.

Lipoproteins The lipoproteins are formed by a combination of protein with a prosthetic group lipid, e. Metaloproteins The prosthetic group is metallic elements such as: Derived Proteins This class of proteins as the name implies, includes those substances formed from simple and conjugated proteins.

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Derived proteins are subdivided into: Primary derived proteins denatured proteins These protein derivatives are formed by agents, such as heat, acids, alkalies, etc. These are synonymous with denatured proteins Figure 4. Proteans These are the earliest product of protein hydrolysis by action of dilute acids or enzymes, e. Metaproteins The metaproteins are formed by further action of acids and alkalies on proteans, e.

Secondary derived proteins These substances are formed in the progressive hydrolytic. The number and sequence of these amino acids are different in different proteins. Protein structure can be classified into four levels of organization: Primary structure 2. Secondary structure 3. Tertiary structure 4. Quaternary structure. The sequence of amino acids forming the backbone of proteins and location of any disulfide bond in a protein is called, the primary structure of the protein Figures 4.

Linkage of many amino acids through peptide bonds results in an unbranched chain called a polypeptide Figure 4. Each amino acid in a polypeptide is called a residue or moiety. Each polypeptide chain is having free amino group at one end called Nterminal and free carboxyl group at another end, called C-terminal. Proteins have unique amino acid sequences that are specified by genes. This amino acid sequence of a protein is referred to as its primary structure.

Clinical Importance of Primary Structure Understanding of primary structure of a protein is important because many genetic diseases result due to an abnormal amino acid sequences. If the primary structure of the normal and mutated proteins are known, this information may be used to diagnose or study the disease.

Thus, regular folding and twisting of the polypeptide chain brought about by hydrogen bonding is called secondary structure of protein. The most important kinds of secondary structure are: If a backbone of polypeptide chain. The helix is a rod-like structure. Thus, CO group of each amino acid is hydrogen bonded to the -NH of the amino acid that is situated four residues ahead in the linear sequence Figure 4.

Helix destabilizing amino acids Glycine and proline are the helix-destabilizing amino acids. N-terminal faces to N-terminal and stabilized by hydrogen bonding. Anti-parallel pleated sheet In the anti-parallel pleated sheet: N-terminal end of one is next to the C-terminal of the other.

N-terminal faces to C-terminal Figure 4. Parallel pleated sheet 2. Other Editions 1. Friend Reviews. To see what your friends thought of this book, please sign up. To ask other readers questions about Essentials of Biochemistry , please sign up. Be the first to ask a question about Essentials of Biochemistry. Lists with This Book. This book is not yet featured on Listopia.

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