2. Thrombin is homologous to the family of serine proteases. What proteolysis can be inferred to occur on fibrinogen?
Involving a catalytic triad similar to the serine proteases.
The difference lies in the binding site (because the catalytic site is the same).
Substrate-specificity allows for differences in enzymes within the serine protease family.
3. Fibrin is a derivative of fibrinogen which is normally present in cells. Explain why fibrin forms clots but fibrinogen does not.
Fibrous aggreggates form.
4. Prothrombin contains g-carboxyglutamate (gla) residues that arise from the post-translational conversion of glutamic acids to gla residues. Prothrombin synthesis requires vitamin K. The role of vitamin K can be described as a cofactor.
5. If an enzyme inhibitor could be the cause for lack of clotting, what type would be most effective and how could it be perfectly designed?
The answer for this one required a little bit of discussion about vitamin K, so don't be too worried if you missed it.
1) The steady-state concentrations of intermediates in metabolic pathways are near equilibrium for some reactions of the pathway and far from equilibrium for others. True or False.
True. The cell requires different levels of different intermediates. Equilibrium, whether it be universal heat death of the universe or submicroscopic, usually implies death.
2) The following represents the biosynthetic pathway for a number of amino acids. Identify the enzymes likely to be regulated by the concentration of each amino acid by drawing an arrow from the endproduct to the enzyme(s) whose activity is likely to be regulated by that endproduct. What types of inhibition are involved at each point of regulation?
---endproducts regulate branch points and 1st committed step.
---when the regulation affects only its own pathway, simple regulation.
---when the regulation affects other pathways (ie at a branch point), cumulative or concerted regulation
3) Comparing cumulative and concerted feedback inhibition, which would be most effective at preventing unnecessary expenditure of energy and carbon compounds when synthesis of only one pathway product is needed?
Cumulative
4) In opposing pathways, a step that is "irreversible" in the cell can be coordinately regulated because:
(c) the step in the opposing pathway uses a different reaction catalyzed by a different enzyme
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