Question 1

Which of the following best describes the structural organization of DNA within a eukaryotic nucleus?

Accepted Answer

DNA is wrapped around histone proteins to form nucleosomes, which further fold into chromatin fibers, loops, and ultimately chromosomes.

Question 2

During DNA replication, which enzyme is responsible for relieving supercoiling ahead of the replication fork?

Accepted Answer

DNA gyrase (topoisomerase)

Question 3

A mutation in the gene encoding the nuclear localization signal (NLS) of a protein would most likely result in:

Accepted Answer

The protein failing to enter the nucleus due to lack of recognition by importin.

Question 4

Which of the following statements about semiconservative DNA replication is correct?

Accepted Answer

Each daughter DNA molecule contains one parental strand and one newly synthesized strand.

Question 5

In mismatch repair, how does the cell distinguish the newly synthesized DNA strand from the template strand?

Accepted Answer

By the methylation state of the DNA.

Question 6

A patient is exposed to a mutagen that acts as a base analogue. Which type of DNA damage is most likely to occur?

Accepted Answer

Incorporation of the analogue into DNA, leading to mispairing during replication.

Question 7

Which of the following best describes the directionality of transcription by RNA polymerase?

Accepted Answer

RNA is synthesized in the $$5' \rightarrow 3'$$ direction.

Question 8

Which posttranscriptional modification is essential for mRNA stability and translation in eukaryotes?

Accepted Answer

Addition of a 5'-cap and a 3'-polyA tail

Question 9

During translation, which site on the ribosome is responsible for accepting incoming aminoacyl-tRNAs?

Accepted Answer

A site

Question 10

Which protein factor is responsible for delivering aminoacyl-tRNA to the A site of the ribosome during elongation in prokaryotes?

Accepted Answer

EF-Tu

Question 11

A mutation causes a premature stop codon in an mRNA. Which cellular mechanism is most likely to degrade this mutant mRNA?

Accepted Answer

Nonsense-mediated decay

Question 12

Which of the following is a reversible posttranslational modification that can regulate protein activity?

Accepted Answer

Phosphorylation

Question 13

Which of the following levels of gene expression regulation is considered posttranscriptional control?

Accepted Answer

Alternative splicing of mRNA

Question 14

During mitosis, the contractile ring responsible for cytokinesis is primarily composed of:

Accepted Answer

Actin and myosin

Question 15

Which checkpoint in the cell cycle is most directly regulated by the tumor suppressor protein p53?

Accepted Answer

G1/S checkpoint

Question 16

In meiosis, homologous recombination occurs during which phase, and what is its primary purpose?

Accepted Answer

Prophase I; to increase genetic diversity

Question 17

Which of the following statements about cyclin-dependent kinases (Cdks) is correct?

Accepted Answer

Cdks require binding to specific cyclins and phosphorylation/dephosphorylation for activation.

Question 18

A cell receives an extrinsic apoptotic signal. Which of the following events is most likely to occur?

Accepted Answer

Activation of caspases leading to programmed cell death

Question 19

Which equation correctly represents the energy requirement for the addition of one amino acid to a growing polypeptide chain during translation?

Accepted Answer

Each addition requires $$1 	ext{ ATP}$$ and $$2 	ext{ GTP}$$ molecules.

Question 20

A protein destined for the mitochondrion is synthesized in the cytoplasm. Which of the following statements is correct regarding its transport?

Accepted Answer

The protein is transported in an unfolded state stabilized by chaperones via the TOM/TIM complexes.

Cell Biology Study Guide: DNA, Gene Expression, and Cell Cycle

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