Biochemistry I (3)

Front 1

Which of the following statements is true of enzyme catalysts?
A) To be effective, they must be present at the same concentration as their substrate.
B) They can increase the equilibrium constant for a given reaction by a thousand fold or more.
C) They lower the activation energy for conversion of substrate to product.
D) Their catalytic activity is independent of pH.
E) They are generally equally active on D and L isomers of a given substrate.

Back 1

C) They lower the activation energy for conversion of substrate to product.

Front 2

Michaelis and Menten assumed that the overall reaction for an enzyme-catalyzed reaction could be written as
`````k1````k2
E + S ⇆ ES --> P
`````k-1
The rate of breakdown of the enzyme-substrate complex can be described by the expression:

A) k1([Et] – [ES])[S].
B) k-1[ES] + k2[ES].
C) k2[ES].
D) k-1[ES].
E) k1([Et] - [ES]).

Back 2

B) k-1[ES] + k2[ES]

Front 3

An enzyme-catalyzed reaction was carried out with the substrate concentration initially 1,000 times greater than the Km for that substrate. After 9.0 minutes, 1% of the substrate had been converted to product, and the amount of product formed in the reaction mixture was 12 mmol. If, in a separate experiment, one-third as much enzyme and twice as much substrate had been combined, how long would it take for the same amount (12 mmol) of product to be formed?
A) 1.5 min
B) 3 min
C) 6 min
D) 13.5 min
E) 27 min

Back 3

E) 27 minutes