Clotting/Regulation of Protein Function

Question 1

Explain covalent modification

Answer 1

Phosphorylation = Adds 2 negative charges, phosphoryl group can H-bonds, Rate of phosphorylation/depho can be adjusted, Allow for amplification effects (one activated enzyme can activate more via kinase cascade e.g. GLYCOGEN BREAKDOWN)

Question 2

Outline proteolytic cleavage

Answer 2

Many enzymes are activated by specific proteolytic cleavage. Digestive enzymes, TRYPSINOGEN –> TRYPSIN, synthesised as zymogens – inactive precursors

Question 3

Outline the common clotting pathway

Answer 3

Factor Xa (activated by intrinsic/extrinsic) = cleavage of prothrombin (kringle domains keep in inactive form) to thrombin. Thrombin = fibrinogen to fibrin. Thrombin activates factor XIII to XIIIa. XIIIa changes fibrin to crosslinked fibrin

Question 4

Describe fibrinogen

Answer 4

Crab shape. 2 sets of tripeptides. Globular structure at ends, connected by chains. α and β chains, high –ve charge, stop fibrinogen coming together. Thrombin chops the ends off = fibrin = can join, stabilised by AMIDE BONDS

Question 5

How could the clotting process be stopped?

Answer 5

DILUTION: of clotting factors by blood flow, removal by liver.

DIGESTION: by proteases: factors Va and VIIIa are degraded by protein C. Protein C is activated by thrombin binding to endothelial receptor, thrombomodulin. Defects in protein C can cause thrombotic disease.

SPECIFIC: Antithrombin III (AT3), enhanced by heparin binding

Question 6

Explain II, VII, IX, X post-translational modification

Answer 6

in liver, add COOH to glutamate forming Gla residues, allows Ca2+ bridge to form between factors and platelets

Question 7

What are the long-term means of enzyme regulation?

Answer 7

Change in rate of protein synthesis and Change in rate of protein degradation

Question 8

what is a zymogen?

Answer 8

inactive precursor (e.g. digestive enzymes)

Question 9

how is the intrinsic clotting pathway activated?

Answer 9

damaged endothelial lining of blood cells promotes binding of factor XII

Question 10

how is the extrinsic clotting pathway activated?

Answer 10

trauma releases tissue factor III

Question 11

what is a kringle domain?

Answer 11

the 2 domains on prothrombin to keep it in its inactive form

Question 12

describe fibrinolysis

Answer 12

streptokinase = plasminogen –> plasmin. Plasmin = fibrin –> fibrin fragments