Question 1

Which scientist's work provided the base composition data that led to the formulation of Chargaff's rules?

Accepted Answer

Erwin Chargaff

Question 2

According to Chargaff's rules, which of the following equations correctly represents the relationship between the bases in double-stranded DNA?

Accepted Answer

$$[A] = [T]$$ and $$[G] = [C]$$

Question 3

Which experimental evidence was critical for Watson and Crick to propose the double helix structure of DNA?

Accepted Answer

X-ray diffraction data from Rosalind Franklin

Question 4

In the Watson-Crick model of DNA, what is the significance of the 2-nm diameter of the helix?

Accepted Answer

It is just right for one purine and one pyrimidine pairing

Question 5

Which feature of DNA allows it to act as a template for replication?

Accepted Answer

The complementary base pairing between strands

Question 6

What is the correct definition of a kilobase (kb) in measuring DNA length?

Accepted Answer

1 kb = 1,000 base pairs

Question 7

Which enzyme is responsible for introducing transient single-strand breaks in DNA to relieve supercoiling?

Accepted Answer

Type I topoisomerase

Question 8

A bacterial cell is found to have highly compact chromosomal DNA. Which process is most likely responsible for this compaction?

Accepted Answer

Supercoiling

Question 9

If a DNA sample has a high GC content, what effect will this have on its melting temperature ($$T_m$$)?

Accepted Answer

It will increase $$T_m$$ due to more hydrogen bonds

Question 10

Which of the following best describes the antiparallel orientation of DNA strands?

Accepted Answer

One strand runs 5' to 3', the other runs 3' to 5'

Question 11

During DNA denaturation, which property of DNA is most commonly measured to monitor strand separation?

Accepted Answer

Absorbance at 260 nm

Question 12

Which of the following statements about DNA gyrase is correct?

Accepted Answer

It can relax positive supercoiling and induce negative supercoiling

Question 13

A researcher uses fluorescence in situ hybridization (FISH) to detect a specific DNA sequence. Which principle does this technique rely on?

Accepted Answer

Nucleic acid hybridization

Question 14

Which of the following interactions is most important for stabilizing the DNA double helix within each strand?

Accepted Answer

Base stacking interactions between adjacent bases

Question 15

If a DNA molecule is twisted further in the same direction as its existing coil, what type of supercoil is formed?

Accepted Answer

Positive supercoil

Question 16

Which process describes the separation of DNA strands by increasing temperature or pH?

Accepted Answer

Denaturation

Question 17

A DNA sample is found to have 30% adenine. According to Chargaff's rules, what percentage of thymine should be present?

Accepted Answer

30%

Question 18

Which of the following is a direct consequence of the double helix model for DNA replication?

Accepted Answer

Each strand serves as a template for synthesis of a new complementary strand

Question 19

Which of the following 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, compared to two in AT pairs

Question 20

Which of the following statements about DNA denaturation and renaturation is correct?

Accepted Answer

Denaturation increases absorbance at 260 nm

DNA Structure: The Structural Basis of Cellular Information

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