Proteins

Shiv Ram krishn

Senior Demonstrator,

Biochemistry, GSMCH.

Syllabus

Definition Sources Classification Simple Proteins Conjugated proteins Derived Proteins Properties

Introduction

Dr. HarpreetAmino acid Chemistry Amino acid definition Structure Classification Structural

Nutritional

Functional Importance Properties Isoelectric pH How amino acids Polymerize to form Proteins?

Definition Of Proteins

Term ProteinBerzeliusFrom Greek Word Proteios meaning: Holding First Place or pre eminent.

Most abundant organic molecules of living system.C= 50-55%H= 6-7.3%O= 19-24%N= 13-19%S= 0-4%

P, Fe, Cu, I, Mg, Mn, Zn

Present in each & every cell.(50% cellular dry weight)

Form fundamental basis of structure & function of life.

Have High Molecular weight.(5000-25,00,000) Nitrogenous macromolecules composed of many

amino acids Unbranched polymers of L-α-aminoacids.

20 standard amino acids in different sequence & different number combine to form indefinite no. of proteins.

How amino acids combine to form protein

Functions of Proteins

Sole source to replace Nitrogen of the body. Enzymes Biochemical catalyst Immunoglobulins IgG, IgA, IgM, IgD, IgE body defence Several Hormones Insulin, Oxytocin Receptors Transport Proteins Albumin Storage Proteins Ferritin Respiratory Pigment, ETC cytochromes, Hemoglobin,

Myoglobin Exert Osmotic Pressure Electrolyte & water balance Blood Clotting Factors Fibrinogen, Thrombin, Prothrombin Provide Energy during prolonged starvation. Associated with structure & strength of body.

Collagen, Elastin Bone matrix, Vascular system Α-keratin epidermal tissues Actin, Myosin Muscle fibre(Contractile proteins)

Sources of proteins Animal Sources

Egg Milk Fish Meat

Pork Beef Mutton chicken

Liver

Plant sources Cereals

Wheat Rice Maize Barley

Legumes Pulses

Red gram Bengal gram Green gram Peas Soyabean

Cashew nut Ground nut Roots &Tubers

Definition in short

Proteins are high molecular weight, nitrogenous, organic macromolecules present in each & every cell of living system forming the fundamental basis of structure and function of life.

Questions Define Proteins. Give the chemical constitution of proteins. Explain the formation of proteins. How? Who coined the term protein? Where are proteins found? What does the term protein means? Give some examples showing structural role of proteins. Give some examples showing dynamic functions of proteins. Name some vegetable sources of proteins. Name some animal sources of proteins.

Any Doubts

Insulin function Glucagon function None other question asked.

Thanks

Classification of Proteins

Shape & SizeFunctional Properties

Solubility & Physical

Properties

Fibrous GlobularDefence proteins

Contractile Proteins

Hormones

Enzymes

Structural proteins

Respiratory Proteins

Simple Proteins

Conjugated Proteins

Derived Proteins

Protamines

Scleroproteins

Glutelins

Gliadins(Prolamines)

Globulins

Albumins

Histones

Nucleoproteins

Metalloproteins

Lipoproteins

Phosphoproteins

Chromoproteins

Glycoproteins

Muco Proteins

Primary derived

Secondary derived

Proteans

Coagulated proteins

Metaproteins

Proteoses

peptides

Peptones

Simple Proteins

Protein type Size & shape

Solubility Insolubility Heat coagulabilit

y

AA+ AA- pI Use Eg.

Protamine small Water

Dilute acid

Dilute alkali

Dilute NH3

_ Arginine rich

Cysteine

Tryptophan

tyrosine

7.4 Basic protein,

N.A+protamine=Nucleoprote

in

Salmine

Sardine

Cyprinine(of fish

sperms & testes)

Histones Water,

Dil. Acid,

Salt solution

NH3 _ Arginine,

Histidine

Alkaline Basic Protein,

N.A. + Histone=Nucle

oprotein,

Porphyrin+Histone=conjugat

ed Protein,

Repressor of template activity of DNA in

synthesis of RNA’

HemoglobinGlobinHistoneHis & lys

rich

Simple proteins contd.

Albumin Water,

Dilute salt solution

Cagulable by heatProductinsoluble in water & dil. Salt solution

Glycine 4.7 Precipitated out of solution by saturation by ammonium

sulfate.

Legumes—legumelin,

Cereals—Leucosin,

Egg—Ovalbumin

Milk--Lactalbumin

Globulins Dilute neutral salt solutions

water + Precipitated by half saturation

with ammonium sulfate or full

saturation with sodium

chloride.

Heme+globulin=Hemopexin,

Heme+metal=Transferrin,

Ceruloplasmin,

Heme+Carbohydrate=Immunoglobulin,

EggsOvoglobulin

MilkLactoglobulin

LegumesLegumin

Gliadin

(Prolamines)

Alcohol(50-80%

C2H5OH)

Water,

Salt soln.,

Absolute alcohol

Proline

Lysine Plant Protein Wheat-Gliadin,

BarleyHordein

Glutelins Large molecules

Dilute acid,

Dilute alkali

Water,

Neutral salt

solution

+ Glutamic acid rich

Rice Oryzein,

Wheat Glutelin

Simple proteins contd.scleroproteins

Keratins Fibrous low Hard keratinHis:Lys:Arg1:4:12,

Soft or pseudokeratinsA.A. not in same ratio,

Neurokeratins1:2:2,

Human Hairalpha keratin cysteine rich,

Beta KeratinGlycine, Alanine rich Cysteine absent

Present in chidermal tissuesuch as horn,

hair, nails, wool, hoofs,

feathers(supporting structures)

spider’s web, silk, reptilian scales

Collagen Long, thin,

partially crystalline

Insoluble in all neutral

salt solvents

Found in connective tissue,Bone

CollagenTannic acidtough, hard,

Collagenboilinggelatinhighly soluble,

easily digestiblecoolgel

no tryptophan

Elastins Alanine, Leucine, Valine, Proline Cysteine, Methionine,

5-Hydroxylysi

ne, Histidine

Found in Connective tissue,

In Yellow elastic fibres,

In ligament, tendon

Formed in large amount during

pregnancy

Elastin is hydrolyzed by pancreatic elastase

Conjugated Proteins

Conjugated Protein= Simple Protein + Prosthetic Group(non Protein group) Holoprotein= Apoprotein + Prosthetic group

Nucleoproteins = Protamine/ Histone + Nucleic acid Deoxyribonucleoproteins: DNA as prosthetic group. Found in Nuclei,

Mitochondria, Chloroplasts. Ribonucleoproteins: RNA as prosthetic group. Found in Nucleoli, ribosome

granules. Nucleoproteins are found in:

Cell Nuclei. As constituent of chromatin Abundant in yeast, Asparagus tip in plants, thymus, glandular organs, sperms.

Conjugated proteins contd.

Mucoproteins or mucoids: Simple Proteins + Mucopolysaccharides(hyaluronic acid, chondroitin sulphate containing >4% N-acetylated hexosamine, uronic acid, sialic acid).

Examples: Mucoproteins found in/as α-ovomucoid & β-ovomucoid of eggwhite. Mucins Blood group substances FSH, LH, HCG Vitreous humor Submaxillary gland Umbilical cord(mucoproteins present in large amount)

Conjugated proteins contd.

Glycoproteins= Simple Protein + Carbohydrate moiety(<4% mannose, galactose, fucose, xylose, arabinose in oligosaccharide chains).

Examples: Mucins Immunoglobulins Complements Many enzymes

Conjugated proteins contd.

Chromoproteins= simple protein + coloured substances. Hemoproteins = simple protein + Heme(red colour)

Hemoglobin in RBC Cytochromes Respiratory chains Catalase H2O2------- H2O + O2 Peroxidase oxidative enzyme

Flavoproteins = simple protein + Riboflavin(yellow colour) it is cellular oxidation reduction protein.

Visual purple =Simple protein + Carotenoid pigment (Purple) Found in retina

Conjugated proteins continued.

Phosphoproteins= simple protein + phosphoric acid as organic phosphate Milk casein Egg yolk ovovitellin

Lipoproteins= simple proteins + Lipids HDL, VLDL, LDL, Chylomicrons.

Metalloproteins= Simple protein + Metal ions(Fe, Co, Mn, Zn, Cu, Mg) Ferritin Fe Ceruloplasmin Cu Carbonic anhydrase Zn

Derived proteins

Simple & conjugated proteins Physical & chemical factors protein products (derived proteins)

Derived proteins are of 2 types: Primary derived proteins Secondary derived proteins

Primary derived proteins These are denatured or coagulated proteins. Molecular weight is same as native protein. Differ in solubility, precipitation & crystallization. Physical & chemical factors involved are Heat, X-rays, UV rays, vigorous shaking, acids,

alkalies. There is intramolecular rearrangement,although peptide bonds remain intact.1. Proteans:

Insoluble products formed by action of water, very dilute acids & enzymes. Eg. Myosan from myosin Edestan from Elastin Fibrin from Fibrinogen

2. Metaproteins: Proteans--acid & alkalies- metaproteins. Soluble in dilute acids & alkalies. Insoluble in neutral solvents.

Eg. Acid & alkali metaproteins.3. Coagulated proteins:

Native protein--- Heat, alcohol-- coagulated protein(insoluble product) Eg.: cooked meat, cooked egg albumin.

Secondary derived proteins

Formed by progressive hydrolysis of proteins at their peptide linkages.

Proteins

Proteoses(Water soluble, Heat coagulable, pptd. By ammonium sulphate)

Peptones(water soluble, Not heat coagulable, Not pptd. By ammonium sulphate, pptd. By phosphotugustic acid.)

Peptides(Water soluble, Not heat coagulable, Not pptd. By ammonium sulphate

Pptd. By phosphotungustic acid)

Complete hydrolysis of protein

Protein Protean Meta protein Proteose Peptone Peptide Aminoacid

General properties of proteins

1. Taste: Tasteless. Hydrolytic products are bitter.2. Odour: Odourless.

Protein heated to dryness-brown colourodour of burning feather.3. Molecular weight: High molecular weight(macromolecules).

S. Albumin= 69000 S. Globulin= 176,000 Fibrinogen= 330,000 Hemoglobin= 67,000 Cytochrome C= 15,600 Pepsin= 35,500 Catalase= 250,000

4. Viscosity: Long molecules(fibrous) more viscous than globular proteins. Eg. Fibrinogen more viscous than albumin.

5. Hydration: Amino(-NH2), and carboxyl(-COOH) group are easily hydrated.6. Amphoteric nature:

Protein molecule-NH2 group as well as –COOH group present these ionize & act as proton donor or acceptorthus protein act as acid and base bothAmpholyte at pI it act as a dipolar ionzwitter ion or hybrid ionnet charge at pI =0.

General properties contd.

7. Heat coagulation: maximum coagulation take place at pI. Proteins get denatured.

8. <----------------------------------------pI-------------------------------------------- acidic alkaline

Protein becomes Protein becomes

cation by accepting proton anion by donating proton

migrate towards anode migrate towards cathode

This property is used for separation of proteins by electrophoresis.

General properties contd.9. Precipitation:

Proteins can be pptd. By some +ve or –ve ions.

this is used for isolation of proteins.

in deproteinization of blood & biological fluids for analysis.

in preparation of protein derivatives.

+ve ions used are: Zn+2, Ca+2, Hg+2, Fe+3, Cu+2, Pb+2

-ve ions used are: Tungstic acid, phosphotungstic acid, trichloroacetic acid, picric acid, tannic acid, ferrocyanic acid, sulphosalicylic acid.

General properties contd.

10. Colour reactions of proteins:

Name of Reaction Colour developed Aminoacid involved

Xanthoproteic reaction Yellow to orange Phenylalanine, tyrosine,tryptophan

Millon’s test Pink red tyrosine

Sakaguchi test Red colour Arginine

Hopkins Cole reaction Tryptophan

Nitroprusside reaction Reddish colour Cysteine

Sullivan reaction Red colour Cysteine, cystine

Lead acetate test Black colour Sulphur containing AA

Biuret reaction Purple violet Histidine & 2 or more peptide linkage

Ninhydrin reaction Blue colour α -Amino acid