Question 1

Which of the following best describes Chargaff’s rules regarding DNA base composition?

Accepted Answer

The number of adenine equals the number of thymine, and the number of guanine equals the number of cytosine.

Question 2

Rosalind Franklin’s X-ray diffraction data was critical in revealing which feature of DNA?

Accepted Answer

The helical structure and regular repeating pattern of DNA.

Question 3

According to the Watson-Crick model, how many base pairs are present per complete turn of the DNA double helix?

Accepted Answer

$$10$$

Question 4

Which statement best explains why DNA with higher GC content has a higher melting temperature ($$T_m$$)?

Accepted Answer

GC pairs are held together by three hydrogen bonds, making the helix more stable.

Question 5

Which enzyme is responsible for introducing negative supercoils into bacterial DNA?

Accepted Answer

DNA gyrase (Type II topoisomerase)

Question 6

A scientist is using fluorescence in situ hybridization (FISH) to detect a chromosomal abnormality. What is the principle behind this technique?

Accepted Answer

FISH uses fluorescently labeled DNA probes that hybridize to complementary sequences on chromosomes.

Question 7

Which of the following best describes the structure of a nucleosome?

Accepted Answer

A nucleosome consists of a histone octamer (two each of H2A, H2B, H3, and H4) with DNA wrapped around it.

Question 8

Which histone is primarily associated with linker DNA between nucleosomes and helps facilitate the formation of the 30-nm chromatin fiber?

Accepted Answer

H1

Question 9

What is the effect of histone acetylation on chromatin structure and gene expression?

Accepted Answer

It leads to looser packing of chromatin and increased gene transcription.

Question 10

Which protein domain is associated with binding acetylated histones and promoting open chromatin (euchromatin) and gene activation?

Accepted Answer

Bromodomain

Question 11

A patient’s cells show a chromosomal region that is permanently compacted and contains highly repetitive DNA sequences. Which type of chromatin is this most likely to be?

Accepted Answer

Constitutive heterochromatin

Question 12

Which of the following is a function of centromeres in eukaryotic chromosomes?

Accepted Answer

Maintaining sister chromatid cohesion and serving as the site for kinetochore formation

Question 13

Which DNA sequence is found at the tips of vertebrate chromosomes and is important for protecting chromosome ends during replication?

Accepted Answer

TTAGGG repeat

Question 14

A forensic scientist is analyzing variable number tandem repeats (VNTRs) in a DNA sample. What property of VNTRs makes them useful for forensic identification?

Accepted Answer

VNTRs are unique to each individual and can be used to distinguish between people.

Question 15

Which of the following statements about bacterial chromosomes is correct?

Accepted Answer

Bacterial chromosomes are usually circular, negatively supercoiled, and localized to the nucleoid.

Question 16

Which process can be monitored by measuring the change in DNA absorbance at $$260\ nm as $$temperature increases?

Accepted Answer

DNA denaturation (melting)

Question 17

Which of the following best describes the role of topoisomerases in DNA structure?

Accepted Answer

They introduce transient breaks in DNA strands to relieve supercoiling.

Question 18

Which type of repeated DNA is most likely to be found scattered throughout the genome and accounts for up to 50% of mammalian DNA?

Accepted Answer

Interspersed repeated DNA

Question 19

A mutation prevents the acetylation of histone tails in a cell. What is the most likely consequence for chromatin structure and gene expression?

Accepted Answer

Chromatin will remain tightly packed, leading to decreased gene expression.

Question 20

Which of the following is a real-world application of nucleic acid hybridization techniques such as FISH?

Accepted Answer

Detecting and localizing specific DNA or RNA sequences in chromosomes, cells, or tissues for diagnostic purposes.

DNA Structure, Packaging, and Chromatin Organization

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