AAMC MCAT Biological and Biochemical Foundations

Question 1

Which enzyme catalyzes the rate-limiting step of glycolysis?

Accepted Answer

Phosphofructokinase-1 (PFK-1)

Answer

PFK-1 catalyzes the irreversible conversion of fructose-6-phosphate to fructose-1,6-bisphosphate, the committed rate-limiting step of glycolysis.

Question 2

What is the net ATP yield from the complete oxidation of one glucose molecule?

Accepted Answer

30-32 ATP

Answer

Complete oxidation yields approximately 30-32 ATP, accounting for the inefficiency of the mitochondrial proton gradient.

Question 3

Which RNA molecule carries amino acids to the ribosome during translation?

Accepted Answer

tRNA

Answer

Transfer RNA (tRNA) carries specific amino acids and matches its anticodon to the mRNA codon at the ribosome.

Question 4

In competitive enzyme inhibition, what happens to Vmax and Km?

Accepted Answer

Vmax unchanged, Km increases

Answer

Competitive inhibitors bind the active site reversibly, raising apparent Km without changing Vmax since high substrate can outcompete the inhibitor.

Question 5

Which organelle is responsible for post-translational protein modification and sorting?

Accepted Answer

Golgi apparatus

Answer

The Golgi apparatus modifies, packages, and sorts proteins from the rough ER for secretion or delivery to other organelles.

AAMC - Association of American Medical Colleges Practice Test