Enzyme Kinetics and Regulation Mechanisms
Enzyme Reactions and Characteristics
1. CH3CH2COO– to CH3CH3 + CO2 – Lyase
2. D-amino acid to L-amino acid – Isomerase
3. Adenylribose + H2O – Hydrolase
4. An enzyme is inhibited competitively, but to varying degrees, by the same concentration of three different inhibitors – Lower Km indicates higher affinity.
5. The figure corresponds to the kinetics of inhibition of an enzyme assay. Curve I could correspond to a curve in the absence of an inhibitor.
6. Isoenzyme is defined as: e. None of the above is correct; the enzyme is bound to a cofactor for activity. (This is the definition of a holoenzyme. Isoenzymes have different structures but catalyze the same reaction.)
7. The graph below corresponds to a type of inhibition called: a. Competitive Inhibition
8. A suicide substrate is a substrate analog that is modified by the enzyme and covalently modifies the enzyme, inactivating it.
9. The curve shape for the kinetics of oxygen binding to hemoglobin: b. The mechanism of oxygen binding causes positive cooperativity in hemoglobin.
10. The enzyme hexokinase catalyzes a reaction where a lower Km indicates higher affinity.
11. Calculate the energy (ΔGº):
- Glutamate + NH3 to Glutamine + H2O: ΔG° = +3.6 kcal/mol
- ATP + H2O to ADP + Pi: ΔG° = -8.0 kcal/mol
- Overall: ΔG° = +3.6 + (-8.0) = -4.4 kcal/mol
12. Energy availability in the cell can be transferred via: c. Phosphorylated compounds, ATP, NADH
13. The coupling of enzyme reactions: e. All of the above
14. The most useful criterion for spontaneity is the calculation of free energy (ΔG).
15. When the value of ΔGº > 0, the change in the system is not spontaneous.
16. Isoenzymes are defined as being encoded in different genes, with different primary structures.
17. In the Michaelis-Menten asymptotic region, the enzyme is almost entirely in the enzyme-substrate complex form.
Additional Enzyme Properties and Kinetics
18. The enzyme β-lactamase.
19. Phosphorylation level reactions are catalyzed by Kinases.
20-21. Regarding different levels… If electrophoretically separated…
22. Initial velocity is defined as the velocity at the beginning of the reaction, where it is approximately constant.
23. In the Lineweaver-Burk plot, the positive value of 1/S, when y = 0, corresponds to -1/Km.
24. Which of the following cofactors is *not* a vitamin? – Glutathione
25. Oxidation-reduction reactions involve cytochromes, quinones, and ubiquinones.
26. A structure stabilized primarily by covalent NH-CO bonds is a secondary structure.
27. The term zymogen: a, b, and c (all of the above)
28. Inhibition by-products occurs when an enzyme in a pathway is inhibited by a product formed by another enzyme located later in the pathway (feedback inhibition).
29. Steady state refers to the relatively constant concentration of the ES complex during the initial phase of the reaction.
30. In a Lineweaver-Burk plot, if the x-intercept is -0.02 (which is -1/Km) and the y-intercept is 0.2 (which is 1/Vmax), then the Km for this enzyme is 50 mM (Km = -1/-0.02 = 50).
31. The Vmax value for this enzyme is 5 μmol/min (Vmax = 1/0.2 = 5).
32. Which of the following reagents destabilizes the secondary structure of proteins? – SDS
33. Activation of enzyme A occurs through allosteric activation and phosphorylation.