Medical Cell Biology and Genetics - Enzymes Flashcards
How do reaction rates vary with enzyme and substrate concentration?
The michaelis menten equation shows how reaction velocity changes with substrate conc.
V0 = Vmax[S] / Km + [S]
(Where Km is the substrate conc that gives 1/2 Vmax)
Increasing enzyme conc = increased Vmax
How does competitive and non competitive inhibition affect Vmax and Km?
Competitive - Vmax unchanged, Km increased
(but adding enough substrate will overcome effect of inhibitor)
Non competitive - Vmax decreased, Km unchanged
What are the allosteric properties of phosphofructokinase?
Phosphofructokinase converts Fructose 6P to fructose 1,6BP
Activators of phosphofructokinase:
AMP, Fructose 2,6BP
Inhibitors of phosphofructokinase:
ATP, Citrate, H+
What is an enzyme cascade?
Activation of one enzyme that leads to further enzymes being activated to amplify the signal.
How do protein kinases and phosphatases regulate cell activity?
Kinases transfer the phosphate group of ATP to an OH group, to form ADP.
Phosphatases remove phosphate groups through hydrolytic activity, which inactivates the protein and causes down signalling.
What are zymogens?
Why are they important?
Inactive precursors of enzymes
They prevent inappropriate enzyme activity eg elastase would digest the pancreas so needs to be transported out the pancreas in an inactive form - proelastase
What is the intrinsic pathway of the clotting cascade?
Occurs when there is damage to the membrane of RBC. Promotes binding of factor XI
What is the extrinsic pathway of the clotting cascade?
Occurs when there is trauma which releases tissue factor III. This causes activation of Factor VII
How does positive feedback result in a clotting cascade?
The activation of thrombin causes further activation of the cascade - means there only needs to be a small amount of initial factor to signal a large cascade.
How are blood clots broken down?
Plasminogen is broken down into plasmin by tissue plasminogen activator and streptokinase.
Plasmin then causes break down of fibrin into fragments.
What factors control the formation of blood clots?
- conc of zymogens: clotting factors can be diluted by blood flow and removed by liver
- digestion by proteases: some factors are degraded by protein C
- specific inhibitors: antithrombin III is enhanced by heparin.
How can the michealis menten equation be rearranged to give a linear plot? and what can we find out from the linear plot?
Reciprocating the michaelis menten equation gives a linear plot (the Lineweaver-Burk plot)
The y intercept = 1/Vmax
The x intercept = -1/Km
The slope = Km/Vmax
