Different types of protein molecules, collagen, elastin, karetin, myoglobin.

1. SIMPLE AND CONJUGATED PROTAIN : -

🐣Simple pro. = serum & albumin.

🐣Conjugated pro = a. acids + non pro. components,

🐣Non protein components called = prosthetic group,

🐣Without prosthetic group = apoprotein & with prosthetic group called = holoprotein.

Conjugated pro;

Simple pro + carbohydrate component = Glycoproteins.

​pro + lipid components = lipoproteins

​pro + metal ions = Metalloproteins

​pro + phosphate group = phosphoproteins

​pro + heme group = Hemoproteins.

2. FIBROUS AND GLOBULAR PROTEINS :-

 🐣Fibrous proteins = long, rod shaped and tough molecules,

🐣Insoluble in water,

🐣Ex. of fibrous protein = keratin, silk fibers & fiber of wool etc

🐣In silk fibers = fibrous pro = fibroin  (Beta sheets).

Fibrous of wool =  kerain pro (alpha- halix).

🐣Globular proteins = compact, spherical & water soluble molecules.

🐣contain several types of IIry structure in spherical molecule,

Outside of molecule = hydrophilic side chain a acids & inner side = hydrophobic side chain a acids are present.

3. COLLAGEN PROTEIN :-

🐣Structural pro, most abundant pro in vertebrates,

🐣present in extracellular matrix.

🐣Triple standard helical structure 

🐣Collagen = 3 left handed alfa helix form 1 right handed collagen,

🐣3 left handed alpha polypeptide chain = each 1000 a acid residues 

🐣Amino acid seq = Gly - Pro - 3 or 4-hydroxyproline or 5-hydroxylysine.

🐣Proline converts into Hydoxyproline by enzyme = propyl hydroxylase &

🐣lysine converts into Hydroxylysine by enzyme = lysil hydroxylase.

🐣 Both enzymes need a cofactor  called = Vitamin C.

🐣Deficiency of v. C = Scurvy,

🐣Scurvy meams = impaired synthesis of collagen.

🐣Structure of collagem molecule is stablished by = interchain H-bonds (N-H & C=O groups are involved).

🐣Hydroxylation of proline & lysine needs = Vitamin C,

🐣Hydroxylation of pro & lys = within ER.

🐣H-bolded triple standard helical molecule called = procollagen,

🐣then procollagen peptidase cleave amino & carboxyl termini of procollagen & make = tropocollagen.

🐣Self assembly of collagen fibrils via covalent cross linking form = collagen fibers.

4. ELASTIN PROTEIN :-

🐣Elastic pro, highly hydrophobic connective tissue protein.

🐣Responsible for extensibility and elastisity.

🐣Elastin pro = In ligaments, lungs & large arteries etc,

🐣Tropoelastin = monomer of Elastin, 72kDa.

🐣Elastin pro = rich in proline sn glycine and some hydroxyproline but no hydroxylysine. 

🐣Tropoelastin = nonpolar - allanine a a & polar segment - lysine rich.

🐣Desmosines fromed from = modifeid Lysine ( tetrafunctional cross link)

🐣Modification of Lysine = deamination of lysine ( removal of omega -NH3+) through enz Lysil oxidase.

5. KERATIN PROTEIN :-

🐣Fribrous protein,

🐣present in = epithelia of all vertebrates, & of two types:

🐣Alfa - karetin (in vegetables) = Tough, nonpolar or insoluble, helical, protofibril

🐣Beta - karetin (in reptiles & birds) = soft and flexible, extended chain, & made from antiparallel beta - pleated sheet.

🐣Alfa - karetin based structures = Horns, scales, claws, hairs, nails, wool feathers etc. 

🐣Polypeptide chain of alfa - karetin = right handed. 

🐣Antiparallel arrangement of prtofilamant - protofibril - microfibril - macrofibril = elastin molecule.

7. MYOGLOBIN :-

🐣Single polyoeptide chain = 153 a a residues.

🐣MW = 17,800 with single heme group.

🐣Inside of myoglobin chain = non polar a a residues & in outside = polar + nonpolar both.

🐣Eight helical segments of heterocyclic ring system.

🐣In heterocyclic ring system = 

🐣and a plot of fractional saturation of myoglobin Y vs partial pressure of O2 (PO2) is = Hyperbolic.

8. Hemoglobin :- i will discuss in next post.