MCAT Biochemistry 3

Question 1

Which protein secondary structure is stabilized by hydrogen bonds between residues distant in primary sequence?

Accepted Answer

Beta sheet

Answer

Beta sheets form hydrogen bonds between backbone atoms of strands that are far apart in the primary sequence, while alpha helices bond residues close together (i and i+4).

Question 2

During the fed state, glucokinase activity in hepatocytes increases because:

Accepted Answer

It is released from a nuclear inhibitor protein

Answer

Glucokinase is sequestered in the nucleus by a regulatory protein at low glucose; when glucose rises, it dissociates and enters the cytoplasm to phosphorylate glucose.

Question 3

Ceramide is the backbone molecule for which class of lipids?

Accepted Answer

Sphingolipids

Answer

Ceramide consists of sphingosine plus a fatty acid and is the core structure of all sphingolipids, including sphingomyelin and glycosphingolipids.

Question 4

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

Accepted Answer

Histidine-Aspartate-Serine triad

Answer

The catalytic triad of serine proteases consists of His, Asp, and Ser working together to activate the serine nucleophile.

Question 5

In the pentose phosphate pathway, transketolase requires which cofactor?

Accepted Answer

Thiamine pyrophosphate (TPP)

Answer

Transketolase, which transfers two-carbon units in the non-oxidative phase of the pentose phosphate pathway, requires thiamine pyrophosphate (TPP) as a cofactor.

MCAT - Medical College Admission Test Practice Test

MCAT - Medical College Admission Test Practice Test

MCAT Biochemistry 3