Question 1

Which of the following best explains why negative supercoiling is advantageous for bacterial chromosomes?

Accepted Answer

It compacts the chromosome and promotes local DNA strand separation required for processes like transcription.

Question 2

A researcher treats E. coli cells with a drug that specifically inhibits DNA gyrase. What is the most likely immediate effect on the bacterial chromosome?

Accepted Answer

The chromosome will accumulate positive supercoils, impairing DNA replication and transcription.

Question 3

Which of the following statements about eukaryotic chromosome organization is CORRECT?

Accepted Answer

Eukaryotic chromosomes contain many origins of replication interspersed throughout their length.

Question 4

A human cell contains a mutation that prevents the production of histone H1. Which chromatin structure would be most directly affected?

Accepted Answer

The formation of the 30 nm fiber would be impaired, resulting in more 'beads-on-a-string' chromatin.

Question 5

Which of the following best describes the difference between constitutive and facultative heterochromatin?

Accepted Answer

Constitutive heterochromatin is always transcriptionally inactive and contains highly repetitive sequences, while facultative heterochromatin can switch between active and inactive states.

Question 6

A scientist digests chromatin with increasing concentrations of DNase I and analyzes the DNA fragments by gel electrophoresis. Which result would best support the nucleosome model?

Accepted Answer

DNA fragments appear as a ladder with bands at approximately 200 base pair intervals.

Question 7

Which of the following equations correctly represents the compaction of DNA from the double helix to the metaphase chromosome, given the following diameters: DNA double helix (2 nm), nucleosome (11 nm), 30 nm fiber, loop domains (300 nm), and metaphase chromosome (1,400 nm)?

Accepted Answer

$$2 \rightarrow 11 \rightarrow 30 \rightarrow 300 \rightarrow 1,400$$

Question 8

Which of the following is a function of SMC proteins in eukaryotic cells?

Accepted Answer

They form dimers that help create and stabilize chromatin loop domains.

Question 9

A patient is treated with Ciprofloxacin for a bacterial infection. What is the molecular target of this drug, and why does it not harm human cells?

Accepted Answer

It inhibits bacterial DNA gyrase, which is not present in human cells.

Question 10

Which of the following best explains why genome size does not always correlate with organismal complexity in eukaryotes?

Accepted Answer

Much of the variation in genome size is due to the accumulation of repetitive DNA that does not encode proteins.

Question 11

Which of the following statements about the human genome is TRUE?

Accepted Answer

Repetitive DNA makes up the majority of the genome, while protein-coding exons account for only about 2%.

Question 12

During mitosis, which protein complex is primarily responsible for holding sister chromatids together until anaphase?

Accepted Answer

Cohesin

Question 13

Which of the following best describes the role of condensin during cell division?

Accepted Answer

Condensin promotes chromosome condensation by organizing chromatin into compact metaphase chromosomes.

Question 14

A mutation prevents the removal of cohesin from chromosome arms during prophase. What is the most likely consequence during mitosis?

Accepted Answer

Sister chromatids may fail to separate properly during anaphase, leading to chromosome missegregation.

Question 15

Which of the following sequences is an example of a highly repetitive DNA element found in the human genome, and what is its approximate length?

Accepted Answer

Alu family; approximately 300 base pairs

Question 16

Which of the following best describes the interaction between histone proteins and DNA in the nucleosome?

Accepted Answer

Positively charged lysine and arginine residues in histones bind to the negatively charged phosphate backbone of DNA.

Question 17

Which of the following best explains the role of CTCF in chromatin organization?

Accepted Answer

CTCF binds to specific DNA sequences and, together with SMC proteins, helps form chromatin loop domains.

Question 18

Which of the following best describes the difference between euchromatin and heterochromatin?

Accepted Answer

Euchromatin is less condensed and transcriptionally active, while heterochromatin is tightly compacted and generally inactive.

Question 19

A chromosome is treated with high salt to remove histones, but loops of DNA remain attached to a central scaffold. What does this observation suggest?

Accepted Answer

Nonhistone proteins, possibly including SMC proteins, help organize metaphase chromosome structure.

Molecular Structure of Chromosomes and Transposable Elements

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