Question

11-Which of the following does NOT regulate biochemical reactions?

A. Regulation of enzyme amounts.

B. Regulation of access of substrates to certain compartments.

C. Alteration of Go' by raising or lowering reactant concentrations

. D. Regulation of the catalytic activities of enzymes.

E. Alteration of the amounts of allosteric modifiers (regulator molecules).

Answer 1

Ans. C. “Alteration of DG⁰ by raising or lowering reactants concentration”.

DG = DG⁰ + RT ln K.    K depends on concentration of reactants and products. Thus, a change in [reactants] may change DG.

However, DG^0’ is measured under physiological conditions of concentration (1M), temperature (37⁰C) and pressure (1 atm.). It’s a standard value and remains constant for the given biochemical reaction. Thus, DG^0’ can’t be altered by changing substrate concentration.

Option A: regulation of enzyme concentration (for example, relative expression of a gene) regulates the number of substrates being catalyzed per unit time.

B. Regulation of access of substrate to certain compartment. For example, glycogen (usually restricted to hepatocytes and myocytes) may be hydrolyzed the enzymes under low blood glucose level. The resultant glucose is then releases into blood and distributed to body cells.

D. Regulation of catalytic activity of enzymes by inhibitors and/or allosteric modulators affect the rate of catalysis.

E. Allosteric modulators may increase or decrease the rate of catalysis after they binds to the allosteric site of the enzyme.