MCAT Biochemistry Quick Quiz

Practice Test

Name: ______________________ Date: __________

Choose the single best answer for each question.

1. The Michaelis constant K_m is defined as:
1. A) The maximum reaction velocity
2. B) The substrate concentration at half V_max
3. C) The turnover number of the enzyme
4. D) The ratio of [E] to [S]
2. Which amino acid is most likely to be found in the interior of a globular protein in aqueous solution?
1. A) Lysine
2. B) Glutamate
3. C) Serine
4. D) Leucine
3. In glycolysis, the net yield of ATP per glucose molecule is:
1. A) 0
2. B) 2
3. C) 4
4. D) 36
4. A competitive inhibitor:
1. A) Decreases V_max but does not change K_m
2. B) Increases apparent K_m but does not change V_max
3. C) Decreases both K_m and V_max
4. D) Binds the enzyme–substrate complex only
5. The peptide bond is best described as:
1. A) An ionic bond
2. B) A non-covalent interaction
3. C) A covalent amide bond
4. D) A disulfide bridge

Answer Key

1. BK_m is the substrate concentration at which reaction velocity is half of V_max. Lower K_m = higher affinity.
2. DLeucine is hydrophobic and tends to bury away from water. Lysine and glutamate are charged; serine is polar.
3. BGlycolysis produces 4 ATP and consumes 2 ATP, for a net gain of 2 ATP per glucose.
4. BCompetitive inhibitors compete with substrate for the active site, raising the apparent K_m. V_max is unchanged because excess substrate outcompetes the inhibitor.
5. CA peptide bond is a covalent amide bond formed between the carboxyl group of one amino acid and the amine group of the next.