MCAT (Biological and Biochemical) 5

Question 1

Which process allows a single gene to produce multiple protein isoforms from the same pre-mRNA?

Accepted Answer

Alternative splicing

Answer

Alternative splicing allows different combinations of exons to be included or excluded, producing multiple distinct mRNA and protein isoforms from a single gene.

Question 2

A patient lacks C3 complement protein. Which immune function is most directly impaired?

Accepted Answer

Opsonization and phagocytosis

Answer

C3b, derived from C3 cleavage, is a major opsonin that coats pathogens and enhances phagocytosis; C3 deficiency severely impairs this innate defense.

Question 3

Which neurotransmitter is primarily responsible for the 'fight-or-flight' response at the adrenal medulla?

Accepted Answer

Acetylcholine

Answer

The adrenal medulla is innervated by preganglionic sympathetic fibers that release acetylcholine, which stimulates chromaffin cells to secrete epinephrine and norepinephrine.

Question 4

Which event occurs during the S phase of the cell cycle?

Accepted Answer

DNA replication

Answer

During the S (synthesis) phase of interphase, the entire genome is replicated so that each chromosome consists of two identical sister chromatids.

Question 5

Which amino acid is most commonly found at the active site of serine proteases?

Accepted Answer

Serine

Answer

Serine proteases (e.g., trypsin, chymotrypsin) use a catalytic triad of Ser-His-Asp, but serine is the nucleophile that attacks the peptide bond.

MCAT - Medical College Admission Test Practice Test

MCAT - Medical College Admission Test Practice Test

MCAT (Biological and Biochemical) 5