What is an enzyme?
A biological catalyst that increases the rate of reaction by providing an alternative reaction pathway with a lower activation energy, facilitate formation of the transition state
Concentration of substrate at half Vmax
What effect does increasing affinity for substrate have on Km?
Increase affinity results in decreased Km
Maximum rate of reaction when all the enzyme's active sites are saturated
What is a non-competitive enzyme inhibitor?
- Non-competitive inhibition is a type of enzyme inhibition where the inhibitor reduces the activity of the enzyme and binds equally well to the enzyme whether or not it has already bound the substrate
- Vmax lowers whilst Km remains the same
What is the Michaelis-Menten equation?
Vo= Vmax x [S] / Km + [S]
Define the international unit of enzyme activity
The enzyme unit is a unit for the amount of a particular enzyme. One unit is defined as the amount of enzyme that produces a conversion of 1 micro mole of substrate a minute
What would be the axis on a Lineweaver-Burk plot
Y axis- 1/V X axis- 1/S
How would Km and Vmax be found from a Linewaver-Burk plot
1/Km- where the graph cuts the X axis
1/Vmax- where the graph cuts the Y axis
What would be the effect of a competitive inhibitor on enzyme kinetics?
Increase Km - lower affinity for substrate Max stays the same
List 5 mechanisms of enzyme control
2) Covalent modification Eg phosphorylation
3) Substrate/product concentration
4) Proteolytic cleavage
5) Long term - Change in rate of protein synthesis/degradation
Describe the effect of an allosteric inhibitor
- Binds to the allosteric site (other than the active site) that brings about a conformational change that decreases its affinity for a substrate
- This CAN NOT be overcome by increasing substrate concentration
What type of enzymes undergo allosteric regulation?
What is the function of kinase enzymes?
Phosphorylates molecules by transfer of the terminal gamma-phosphate from ATP to the OH group of Ser, The, Tyr Eg hexokinase in step 1 of glycolysis
Define the term zymogen
Inactive precursor of an enzyme which is activated by proteolytic cleavage
What are the intrinsic and extrinsic pathways of blood clotting
Intrinsic - activated by membrane damage, trauma inside the vascular system
Extrinsic - Activated by external trauma to tissue, outside the vascular system
List the factors involved in the intrinsic pathway of the blood clotting cascade
XI, IX, X (VII, V)
List the factors involved in the extrinsic pathway of the blood clotting cascade
III, VII, X
How is positive feedback involved in the blood clotting cascade?
Prothrombin is cleaved to thrombin which feeds back to factors XI, VIII and V which continues activation of the intrinsic pathway
How are gla domains formed?
Glutamate residues on factors II, VII IX and X are carboxylated in the liver to form gla domains
What are the functions of gla domains?
- Allow interaction with sites of damage as prothrombin binds calcium via Gla residues
- Brings together clotting factors as only prothrombin next to damaged site will be activated
How is a fibrin clot stabilised?
Peptide bonds form between lysine and glutamine residues catalysed by transglutaminase
Describe the process of fibrinolysis?
Breakdown of the fibrin clot by conversion from plasminogen to plasmin (fibrin fragment) by streptokinase and t-PA when proteolytically activated
How is the clotting cascade process stopped?
- Localisation of prothrombin by diluting factors by blood flow to liver
- Digestion by proteases Eg protein C
- Specific inhibitors Eg Antithrombin III
Name three methods of regulation if the blood clotting cascade
- Inactive zymogens at low concentrations
- Amplification of signal by cascade mechanism
- Feedback activation by thrombin
- Multiple termination mechanisms
- Clustering factors at site of damage
- Clot breakdown controlled by proteolytic activation
What is plasmin?
A serine protease that acts to dissolve fibrinblood clots