OAT Cell and Molecular Biology 3

Question 1

Which component of the electron transport chain directly reduces molecular oxygen to water?

Accepted Answer

Complex IV

Answer

Complex IV (cytochrome c oxidase) is the terminal oxidase that transfers electrons from cytochrome c to O₂, producing water.

Question 2

In eukaryotes, which histone modification is most strongly associated with transcriptionally active chromatin?

Accepted Answer

H3K4 trimethylation

Answer

H3K4me3 marks active gene promoters and is associated with open, transcriptionally permissive chromatin.

Question 3

What is the function of the Okazaki fragment ligase step during lagging strand synthesis?

Accepted Answer

It joins adjacent Okazaki fragments

Answer

DNA ligase seals the nick between adjacent Okazaki fragments by forming a phosphodiester bond after primer removal and gap filling.

Question 4

Which receptor type works by dimerizing and activating an intrinsic tyrosine kinase domain upon ligand binding?

Accepted Answer

Receptor tyrosine kinase

Answer

Receptor tyrosine kinases (e.g., EGF receptor) dimerize upon ligand binding and trans-autophosphorylate their intracellular kinase domains.

Question 5

Which organelle is the primary site of fatty acid beta-oxidation in animal cells?

Accepted Answer

Mitochondrial matrix

Answer

Beta-oxidation of long-chain fatty acids occurs predominantly in the mitochondrial matrix, generating acetyl-CoA, NADH, and FADH₂.

OAT - Optometry Admission Test Practice Test