Consider the two chemical reactions. Identify each statement following as true or false, and clarify as needed.

Question

A +B ?C
C ?A +B

A. The enzyme catalyzing the formation of C must be different from that catalyzing the breakdown of C.
B. The enzyme catalyzing the formation of C must be the same as that catalyzing the breakdown of C.
C. Only one of the reactions could occur in a given cell or system.
D. Both reactions must be occurring in an equilibrium situation.
E. Equilibrium is always achieved in a chemical reaction.
F. Equilibrium can be prevented from occurring by constantly removing the product of either reaction.
G. An equilibrium, once established, cannot be disturbed.

Answer 1

A. False. There may be more than one enzyme for the reactions listed, but a given enzyme is often capable of
performing a reaction in both directions.
B. False. The enzyme for both reactions could be the same, but often a particular enzyme is more likely to perform
the forward reaction while a different enzyme is more likely to perform the reverse.
C. False. If the reactions are at equilibrium, both are occurring at the same time. If they are not at equilibrium, it is
possible that the reaction is occurring only in one direction. In addition, cells can have different enzymes for each
reaction direction that can be differentially controlled (i.e., one active and the other inactive).
D. True. By definition, a reaction is at equilibrium when both directions are occurring such that there is no net
change in amounts of substrates and products.
E. False. Equilibrium is not necessarily established, especially in a cell where a product is immediately removed
from the system for use elsewhere, such as the product ATP, or if a given enzyme does not perform the reverse
reaction.
F. True. Any change in amounts of enzyme, substrate, or product will disturb equilibrium, and if these things
constantly change, equilibrium cannot be established.
G. False. Equilibrium can be disturbed by changing the amount of enzyme, substrate, or product, or by altering the
enzyme's efficacy by changing temperature or pH.