Cell and Molecular Biology Flashcards

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

Answer: Complex IV

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

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

Answer: H3K4 trimethylation

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

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

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.

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

Answer: Receptor tyrosine kinase

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

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

Answer: Mitochondrial matrix

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

Which RNA polymerase transcribes pre-rRNA (28S, 18S, 5.8S) in eukaryotes?

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.

The CRISPR-Cas9 system requires which RNA component to direct the nuclease to its genomic target?

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.