Question

12. Which of the following statements is true of enzyme catalysts? A B C To be effective, they must be present at the same concentration as their substrate. They can increase the equilibrium constant for a given reaction by a thousand-fold or more. They lower the activation energy for conversion of substrate to product. Their catalytic activity is independent of pH. They are generally equally active on D and L isomers of a given substrate. D E 13. In competitive inhibition, an inhibitor: A binds at several different sites on an enzyme. B binds covalently to the enzyme. C binds only to the ES complex. D binds reversibly at the active site. E lowers the characteristic Vmax of the enzyme 14. One of the enzymes involved in glycolysis, aldolase, requires Zn2- for catalysis. Under conditions of zinc deficiency, when the enzyme may lack zinc, it would be referred to as the: A apoenzyme. B coenzyme. C holoenzyme. D prosthetic group. E substrate. 15. A metabolic pathway proceeds according to the scheme, R-S-T-U-V-W. A regulatory enzyme, X, catalyzes the first reaction in the pathway. Which of the following is most likely correct for this pathway? A Either metabolite U or V is likely to be a positive modulator, increasing the activity of X. B The first products, is probably the primary negative modulator of X, leading to feedback inhibition C. The last product, W, is likely to be a negative modulator of X, leading to feedback inhibition. D The last product, W, is likely to be a positive modulator, increasing the activity of X. E The last reaction will be catalyzed by a second regulatory enzyme.

Answer 1

12. A and C are true

​​​For an effective chemical reaction, concentration of substrate and enzyme should be equal. Enzyme activities are depends on pH and are do not change the equilibrium constant for a reaction but it lowers the activation energy of the substrates. Enzymes are active on either L-isomer or D-isomer, because the enzymes are specific to it's purticular functional group of purticular substrate.

13. B and D

In competitive inhibition, the inhibitor resembles the normal substrate and thereby binds to the active site of enzyme and prevents the substrate from binding. The inhibitor covalently binds to the particular group at the enzyme's active site and inaactivates the enzyme. The competitive inhibitor not binds on the enzyme-substrate complex (E-S complex), but to the substrate. The competitive inhibitor does not change the catalysis of enzyme-substrate complex and therefore, it do not change Vmax. Competitive inhibition is reversible or irreversible but usually it is temporary, and the inhibitor eventually leaves the enzyme.