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
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