OAT Cell and Molecular Biology 3 — Questions and Answers
Question 1: Which component of the electron transport chain directly reduces molecular oxygen to water?
- Complex I
- Complex II
- Complex III
- Complex IV (Correct answer)
Correct answer: Complex IV
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?
- H3K9 methylation
- H3K27 trimethylation
- H3K4 trimethylation (Correct answer)
- H2A ubiquitination
Correct answer: H3K4 trimethylation
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?
- It synthesizes the RNA primer
- It removes the RNA primer
- It joins adjacent Okazaki fragments (Correct answer)
- It proofreads newly synthesized DNA
Correct answer: It joins adjacent Okazaki fragments
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?
- G protein-coupled receptor
- Receptor tyrosine kinase (Correct answer)
- Ligand-gated ion channel
- Nuclear receptor
Correct answer: Receptor tyrosine kinase
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?
- Smooth endoplasmic reticulum
- Peroxisome
- Mitochondrial matrix (Correct answer)
- Cytoplasm
Correct answer: Mitochondrial matrix
Beta-oxidation of long-chain fatty acids occurs predominantly in the mitochondrial matrix, generating acetyl-CoA, NADH, and FADH₂.
Question 6: Which RNA polymerase transcribes pre-rRNA (28S, 18S, 5.8S) in eukaryotes?
- RNA Pol I (Correct answer)
- RNA Pol II
- RNA Pol III
- RNA Pol IV
Correct answer: RNA Pol I
RNA Polymerase I transcribes the 45S rRNA precursor in the nucleolus, which is processed into 28S, 18S, and 5.8S rRNAs.
Question 7: The CRISPR-Cas9 system requires which RNA component to direct the nuclease to its genomic target?
- siRNA
- Guide RNA (gRNA) (Correct answer)
- Ribozyme
- snRNA
Correct answer: Guide RNA (gRNA)
A single guide RNA (sgRNA) contains a 20-nt spacer sequence complementary to the target DNA that directs Cas9 to the correct genomic locus.
OAT Cell and Molecular Biology 3
Which component of the electron transport chain directly reduces molecular oxygen to water?