PCAT Biochemistry 3

Question 1

In competitive inhibition, increasing the substrate concentration will:

Accepted Answer

Leave Vmax unchanged and increase apparent Km

Answer

Competitive inhibitors bind the active site reversibly; adding excess substrate outcompetes the inhibitor, so Vmax is unchanged but the apparent Km is increased.

Question 2

Which lipoprotein is primarily responsible for transporting dietary (exogenous) triglycerides from the intestine to peripheral tissues?

Accepted Answer

Chylomicrons

Answer

Chylomicrons are assembled in intestinal epithelial cells and carry absorbed dietary triglycerides through the lymphatic system to peripheral tissues.

Question 3

Sickle cell disease results from a single amino acid substitution in hemoglobin. What change occurs?

Accepted Answer

Glutamate is replaced by valine at position 6 of the beta chain

Answer

A point mutation converts the GAG codon to GTG, replacing the hydrophilic glutamate with hydrophobic valine at position 6 of the beta-globin chain, causing HbS polymerization under low oxygen conditions.

Question 4

Which fatty acid is classified as an omega-3 fatty acid?

Accepted Answer

Alpha-linolenic acid (18:3)

Answer

Alpha-linolenic acid (ALA, 18:3Δ9,12,15) is an omega-3 fatty acid because its first double bond is at the 3rd carbon from the methyl end; it is an essential fatty acid.

Question 5

Which enzyme is responsible for unwinding the DNA double helix during replication?

Accepted Answer

Helicase

Answer

Helicase uses ATP hydrolysis to break hydrogen bonds between base pairs and unwind the double helix at the replication fork.

PCAT - Pharmacy College Admission Test Practice Test

PCAT - Pharmacy College Admission Test Practice Test

PCAT Biochemistry 3