Topic- Proteins Presented - PowerPoint Presentation

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Topic-ProteinsPresented byMs. P. H. GiriDepartment of MicrobiologyDeogiri College, Aurangabad

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B.Sc. F. Y.Semester IIPaper No. VBasic BiochemistryUnit 3 ProteinsMs. Priyanka H. Giri

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CLASSIFICATION OF PROTEINS :Proteins can be classified by two ways:I. According to solubilityII. On the basis of increasing complexity into their structures. (I) According to solubility:According to solubility, proteins are divided into two groups:1) Fibrous Proteins2) Globular Proteins

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(1) Fibrous Proteins:These proteins appear like fibres made of linear molecules that are arranged roughly parallel to the fibre axis. The long linear chain proteins are held together by intermolecular hydrogen bonds.These are highly resistant to digestion by proteolytic enzymes.These are insoluble in common solvents but are soluble in concentrated acids and alkalies.Fibrous proteins include the proteins of silk, wool, skin, hair, horn, nails, hoofs, quills, connective tissue and bone.

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(2) Globular Proteins:These are highly branched and cross-linked condensation products of basic or acidic amino acids. The polypeptide chains are held together by cross-linked groups or in an aggregate state. The aggregates may also be folded to three-dimensional structures by weak non-covalent bonds.These are soluble in water and in dilute acids, alkalies and salts.Globular proteins include all the enzymes, oxygen carrying proteins, protein hormones, etc. 

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(II) On the Basis of Increasing Complexity into their Structures : According to this system of classification, proteins may be divided into three main groups:  (1) Simple Proteins(2) Conjugated Proteins (3) Derived Proteins 

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1) Simple Proteins:The simple proteins are those proteins which yield only amino acids on hydrolysis.(a) Albumins:These are - (i) Soluble in water(ii) Coagulated by heat(iii) Precipitated at high salt concentration Examples - Serum albumin, plasma albumin, egg albumin, lactalbumin, legumelin, etc. 

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(b) Globulins: These are - Insoluble in waterCoagulated by heat Precipitated by half saturated salt solutions.Examples - Plasma globulins, serum globulins, vitellin, tuberin, legumin, myosinogen, etc.

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(c) Glutelins :These are – Insoluble in water Soluble in acids and basesCoagulated by heat Examples - Glutelin (Wheat), Oryzenin (Rice), etc.

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(d) Prolamines: These are - (i) Insoluble in water, but soluble in ethanol (ii) Not coagulated. Examples - Gliadin (Wheat), Zenin (Maize), etc.

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(e) Protamines:These are - (i) Soluble in water(ii) Not coagulated by heat Examples - Salmine (Salmon sperm of fish)

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(f) Histones :These are - (i) Water soluble(ii) Not coagulated by heat Examples - Globin of haemoglobin and thymus histones(g) Scleroproteins (albuminoids) : These are water insoluble.Examples - Keratin (Hair, horn, nail), collagen (Skin, bone tendons), Elastin (ligaments)

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(2) Conjugated Proteins: These contain simple protein molecules united with non-protein group and on hydrolysis they yield other non-proteinous substances in addition to amino acids.The non-proteinous moiety is referred as 'prosthetic group.'(a) Nucleoproteins: Proteins with nucleic acid e.g. Nucleoprotamines and nucleohistones(b) Lipoproteins: Proteins with lipidse.g. Lipoproteins of egg yolk, milk and cell membranes and lipoptoteins of blood.(c) Glycoproteins: Proteins with carbohydrates e.g. Mucin (Saliva), Ovomucoid (egg yolk), etc.(d) Phosphoproteins: Contain phosphorus radical as prosthetic group.e.g. Caseinogen (milk), Ovovitellin (egg yolk) etc.

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(e) Metalloproteins: Contain metal ion as prosthetic group, (i.e. Zn++, Co++, Fe++, Cu++, Mg++, Mn++, etc.) e.g. Siderophillin (Fe++), Ceruloplasmin (Cu++) etc.(f) Chromoproteins: Contain porphyrin with a metal ion, as their prosthetic group.e.g. Haemoglobin, myoglobin, catalase, cytochrome, peroxidase etc.(g) Flavoproteins: Contain riboflavin as prosthetic group e.g. Flavoproteins of liver and kidney.

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(3) Derived Proteins: The derived proteins are the intermediate hydrolysis products, which are formed by the action of physical (heat), chemical or enzymatic agents on natural proteins.(a) Primary derivatives :(i) Proteans - e.g. fibrin from fibrinogen(ii) Metaproteins - e.g. acid and alkali meta proteins(iii) Coagulated proteins - e.g. cooked- proteins and coagulated albumin. 

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(b) Secondary derivatives (i) Proteoses - e.g. albumose, globumose(ii) Peptones(iii) Peptides - e.g. glycyl-alanine, leucyl-glutamic acid  

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BIOLOGICAL IMPORTANCE / FUNCTIONS OF PROTEINSProteins are the most common macromolecules in all biological systems and all biochemical changes need proteins, proteins are known by their functions first and then by the structures. Proteins are classified according to their functions. (1) Enzymes: These are biological catalysts essential for biochemical changes. All enzymes are proteins.(2) Transport of Carrier Proteins: Transportation of metabolites; gases are facilitated via proteins. For example haemoglobin transport oxygen and carbon-dioxide, Na+, K+, ATPase. Pump transport Na+ and K+ ions, Plasma lipoprotein transport fat and fat-soluble metabolites.

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(3) Defense Proteins: These proteins protect from bacterial, viral infection and toxic substances. Antibodies are-produced in the body against antigen, interferons are produced against viral infection.(4) Structural Proteins: There are proteins which give definite shape and strength to cell, tissue organ and body. For example, proteins of cytoskeleton, collagen and cartilage.

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(5) Regulatory proteins: Homeostalsis is most common and important phenomena seen in all biological systems, in which concentration of certain metabolites, pH of various body fluid, osmotic pressure, temperature, and electrolytes are regulated with the help of proteins. For example, insulin regulates blood sugar, parathyroid hormone regulates blood calcium.(6) Muscle proteins: These proteins carry out mechanical work.

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(7) Membrane proteins:Proteins and lipids are the major structural component of cell membranes.The proteins associated on membrane consist of 'integral' or 'intrinsic' proteins and 'peripheral' or 'extrinsic' proteins.The integral proteins include 'translocases', which regulate the movement of substances across the membrane. The peripheral proteins include 'cytochrome - C and 'mono-amine oxidase;' these play an important role in metabolism or biotransformation.Many enzymes are the components of the electron transport chain, associated with the membrane.(8) Hormones:Several hormones are peptides and proteins. They play an important role in the regulation of metabolic reaction.

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(9) Blood proteinsThe blood proteins include the 'plasma proteins,' and 'haemoglobin'.Plasma proteins consist of 'globulins' and 'fibrinogen1. The y-globulins play an important role against body defence mechanism by forming antibodies, while fibrinogen is an important blood clotting factor.Albumin is synthesized in liver and maintains the colloid osmotic pressure of plasma and takes part in transport of a variety of materials like bilirubin.

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Hapatoglobin is an α2-globin. When R.B.C. are damaged, the released haemoglobin into the plasma is bound by hapatoglobin and thus prevented from being excreted through urine.α2-Macogloulin is an inhibitor of proteolytic enzymes. Transferin, is a (i-globulin involved in the transfer of Fe++ in plasma. Lipo-proteins are concerned with transport of fat in blood.

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Haemoglobin is a conjugated protein consisting of haeme + globin. It is responsible for the transfer of gases in the body.Nucleoproteins are conjugated proteins of cell nuclei. Antibiotics: Some antibiotics are peptides; e.g. Penicillin – G. Collagen: It is a fibrous protein found in many connective tissues, consists of three helically coiled linear chains, each of about 1,000 amino acids. The amino acid composition of collagen is 25 % glycine and

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Enzymes: The term ‘enzyme’ was coined in 1878 by Friedrich Wilhelm Kuhne to designate these ‘biological catalysts’ that had previously been called 'ferments'. As they quicken most of the chemical reactions occurring in the body,The name Enzyme (en = in; zyme = yeast) literally means ‘in yeast’. This was referred to denote one of the most noteworthy reactions wherein the production of ethyl alcohol and carbon dioxide through the agency of an enzyme, the zymase, present in yeast takes place. This reaction is most popularly known as alcoholic fermentation.

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Definition of enzymeEnzymes are biological catalysts, which accelerate the rate of biochemical reactions without changing themselves.

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Co-enzyme, Apoenzyme and Holoenzyme: Enzymes are proteins or proteins combined with other chemical groups. The low molecular weight organic molecule associated with proteins in the enzyme is called co-enzyme. The protein portion is called apoenzyme. Apoenzyme and coenzyme together form complete enzyme called holoenzyme.Apoenzyme + Co-enzyme = Holoenzyme (Protein part) (Organic part) (Complete Enzyme) (Inactive) (Inactive) (Active)

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Important properties of enzymes All enzymes except 'ribozyme' are protein or protein combined with other chemical group.As being an organic catalyst, it increases the rate of cellular reactions.Each enzyme has a unique characteristic shape, specificity and function.It provides a reaction site for substrate.It combines with substrate forming an enzyme substrate complex (Es complex) as an intermediate but does not convert or does not integrate in the product formed.As it is protein in nature, the activity is affected by different environmental factors like pH, temperature, etc.They have high catalytic efficiency and require mild reaction conditions.They cannot pass through semi permeable membrane.Enzymes are bulky, molecular weights range from 10,000 to million.The enzyme activity can be regulated, may be by feedback inhibition or at genetic level.

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ACTIVE SITE:As the substrate molecules are comparatively much smaller than the enzyme molecules, there should be some specific regions or sites on the enzyme for binding with the substrate. Such sites of attachment are variously called as 'active sites' or 'catalytic sites' or 'substrate sites'.Although the enzymes differ widely in their properties, the active site present in their molecule possesses some common features. These are listed below:

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1) The active site occupies a relatively small portion of the enzyme molecule.2) The active site is neither a point nor a line or even a plane but is a 3-dimensional entity. It is made up of groups that come from different parts of the linear amino acid sequence. For example, lysozyme has 6 subsites in the active site. The amino acid residues located at the active site are 35, 52, 59, 62, 63 and 107. in case of ribonuclease enzyme, histidine residues 12 and 119 are only required for action while in case of chymotrypsin, histidine residue 57 aspartic acid residue 102, serine residue 195 are playing important role in catalytic function.

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3) Usually the arrangement of atoms in the active site is well defined, resulting in a marked specificity of the enzymes. Although cases are known where the active site changes its configuration in order to bind a substance which is only slightly different in structure from its own substrate.4) The active site binds the substrate molecule by relatively weak forces.5) The active sites in the enzyme molecules are grooves or crevices from which water is largely excluded. It contains amino acids such as aspaitic acid, glutamic acid, lysine serine etc. The side chain groups like —COOH, —NH2, —CH2OH etc., serve as catalytic groups in the active site. Besides, the crevice creates a micro-environment in which certain polar residues acquire special properties which are essential for catalysis.

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Physico chemical factors Affecting Enzyme Action: 1. Temperature 2. pH 3. Substrate concentration 4. Enzyme concentration 5. Concentration of products 6. Light 7. Ions

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1. Effect of Temperature: When all the other parameters are kept constant (i.e. at their optimum level), then the rate of enzyme reaction increases slowly with increase of temperature till it reaches a maximum. Further increase in temperature denatures the protein resulting in decrease in the enzyme action and a further increase in temperature may totally destroy the protein.

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2. Effect of pH: When all the other parameters are kept constant, the velocity of an enzyme catalysed reaction increases till it reaches the optimum pH and then decreases with further increase/decrease in pH. The activity is maximum for most of the enzymes at the biological pH of 7.4. Optimum pH for pepsin is 1.5, acid phosphatase is 4.5 and for alkaline phosphatase it is 9.8.

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3. Effect of Substrate Concentration: When all the other parameters are kept constant including the enzyme concentration, then, as the substrate concentration increases the rate of reaction increases steadily, till the enzyme is saturated with the substrate. At this stage the reaction rate does not increase and remains constant.

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4. Effect of Enzyme Concentration: As the enzyme concentration increases, the rate of reaction increases steadily in presence of an excess amount of substrate, the other factors being kept constant. A linear curve is produced.

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5. Effect of Products: When the product is more in the reaction mixture, then the rate of reaction decreases due to feedback inhibition. 6. Effect of Light: The speed of activity of various enzymes changes in different wavelength of light ex. blue light enhances the activity of salivary amylase whereas, U.V. light decreases the velocity. 7. Effect of Ions: Presence or absence of particular ions enhances or reduces the activity of enzymes ex. Pepsinogen is converted to pepsin in presence of H+ ions. Kinases act in presence of Mg+2 ions.