enzyme activity and protein regulation

Question 1

what is the Km value?

Answer 1

represent affinity of an enzyme for its substrate

Question 2

define an irreversible enzyme

Answer 2

binds tightly

forms covalent bond

Question 3

define a reversible enzyme

Answer 3

can freely dissociate

competitive - binds at active site, affects Km not Vmax

non competitive - binds to alternate site, affects Vmax

Question 4

what are the three stages of haemostasis?

Answer 4

Vascular spasm - smooth muscle contracts

platelet plug - platelet attach to exposed vessels, chemicals released make platelets sticky and plug forms

coagulation - fibrin forms mesh traps RBCs forms clot

Question 5

explain intrinsic pathway

Answer 5

activated by trauma within vascular system

results in clot

less rapidly activated

factor IX or X targeted to membrane Gla domains

Question 6

explain extrinsic pathway

Answer 6

activated by external trauma

blood loss form vascular system

more rapidly activated

exposes extracellular domain of tissue factor III

Question 7

how is clotting stopped?

Answer 7

localisation of prothrombin - dilution of clotting factors removed by liver

specific inhibitors - antithrombin III, enhanced heparin, inactivation of factors

digestion by proteases - FVa and VIIIa degraded

Question 8

how are clots removed?

Answer 8

fibrinolysis

Question 9

name 3 main sites of anticoagulation

Answer 9

vitamin K antagonists - warfarin

heparin - activates antithrombin III

oral anticoagulants - new class

Question 10

what are the control points in blood clotting?

Answer 10

inactive zymogens at low concentrations
undergo proteolytic activation
initial signal by cascade amplified
clotting factors at site of damage
feedback activation by thrombin
clotting stopped by multiple mechanisms
clot breakdown by proteolytic activation