Synthesis of Collagen

Image taken from WikiMedia [link]

1) Formation of pro- α-chain

2) Hydroxylation

3) Glycosylation

4) Assembly and secretion

5) Extracellular cleavage of procollagen molecule

-genes for pro α1 and α2 are transcribed into mRNA’s

-mRNA’s is transcribed to pre pro- α polypeptide chain that are extruded into ER

-Selected proline and lysine residues are hydroxylated

-Selected lysine residue are glycosylated with glucose and galactose

-Three pro-α- chain assembles #intra and inter disulfide bond form at C-terminal polypeptide extension

-Triple helix forms by zipper like folding

-Procollagen molecule secreted from golgi vacuole to ECM

-N terminal and terminal propeptides cleaved by procollagen peptidases

-Self assembly of collagen molecules into fibrils and subsequent cross linking

Picture Summary

Image taken from Oulun Yliopisto

Role of Ascorbic Acid and α-antitrypsin

Describe the importance of:

1. ascorbic acid in collagen synthesis
2. α-antitrypsin in elastin degradation (10minutes)

Ascorbic acid

-is a reducing agent

-require for action of prolyl hydroxylase and lysyl hydroxylase

-to produce hydroxyproline and hydroxylysine from hydroxylation of prolyl and lysyl

-important for formation of cross linking of collagen fiber

-if no asorbic acid or deficient, lead to Scurvy

α-antitrypsin

-inhibit a number of proteolytic enzyme that hydrolyze and destroy protein

-it has important role in inhibition of neutrophil elastase

-elastase can degrade elastin, therefore weaken structure like alveolar wall

-therefore, α-antitrypsin inhibit the action of elastase

DNA Repair Mechanism

Describe the mechanism of DNA repair (5 minutes)

-Recognition of altered or distorted part in helix

- Winding of helix

-Removal of damaged part by endonuclease

- DNA polymerase replaces the removal part with dNTP by using undamaged strand as template

-DNA ligase seal the repaired strands

How the cell overcome DNA Mutation

Describe how the cell overcome the DNA mutation (5 marks, Selanjar 1 06/07)

-Proof reading after the copying of template finish

-Strand-directed Mismatch Repair System

-Enzyme that use forces from sun light to break the bonds between dimer.

-Mismatch repair mechanism

-base excision repair mechanism

-Nucleotide excision repair mechanism

Regulation of Enzyme Activity

Outline the regulation of enzyme activity (10 minutes)

Sub cellular compartmentalization

-Enzyme located in specific cellular organelles (eg mitochondria)

-each organelles surround by membrane with unique permeability properties

-these membrane regulate entry or exit of substrate/product

Induction of enzyme synthesis

-Some enzyme are synthesized only when substrate is available

-thus, enzyme activity are regulated by substrate

Zymogen activation

-Enzyme is secreted as larger inactive proenzyme

-zymogen is activated by specific mechanism that cleaves larger inactive enzyme to active enzyme

examples

trypsinogen to trypsin

pepsinogen to pepsin

Product inhibition

-Higher concentration of substrate binds to enzyme and inactivate it

-for example, inhibition of hexokinase by glucose 6 phosphate

-mainly for enzyme that catalyze unidirectional reaction

Feedback inhibition

-inhibition of first enzyme in a sequence of metabolic reaction by the product of last enzyme

-eg regulation of cholesterol synthesize by cholesterol through feedback inhibition of enzyme HMG coA reductase

Covalent modification

-Regulation of metabolism according to physiological need

-phosphorylation/dephosphorylation of enzyme by cAMP mediated mechanism

eg : phosphorylation of glycogen phosphorylase activate it

phosphorylation of glycogen synthase inactivate it

Allosteric regulation

-other site than active site

-regulated by allosteric activator and inhibitor