Question 1

Which scientist's X-ray diffraction data was critical in helping Watson and Crick determine the double helix structure of DNA?

Accepted Answer

Rosalind Franklin

Question 2

According to Chargaff’s rules, which of the following is always true for double-stranded DNA from any species?

Accepted Answer

The amount of adenine equals the amount of thymine

Question 3

What is the structural feature of DNA that allows it to serve as a template for replication?

Accepted Answer

The antiparallel and complementary nature of its two strands

Question 4

Which of the following best describes the orientation of the two strands in a DNA double helix?

Accepted Answer

One strand runs 5' to 3', the other runs 3' to 5' (antiparallel)

Question 5

A DNA molecule is found to have 20% cytosine. According to Chargaff’s rules, what percentage of adenine would you expect?

Accepted Answer

30%

Question 6

Which type of bond holds the two strands of DNA together?

Accepted Answer

Hydrogen bonds

Question 7

What is the effect of increasing the GC content of a DNA molecule on its melting temperature ($$T_m$$)?

Accepted Answer

It increases $$T_m$$ because GC pairs have three hydrogen bonds

Question 8

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

Accepted Answer

DNA gyrase (Type II topoisomerase)

Question 9

If a circular DNA molecule is relaxed and then twisted further in the same direction as its helix, what type of supercoiling is introduced?

Accepted Answer

Positive supercoiling

Question 10

Which of the following best explains why DNA absorbs more light at 260 nm when denatured?

Accepted Answer

Single-stranded DNA has more exposed bases, increasing absorbance

Question 11

Which process can be monitored by measuring changes in absorbance at 260 nm?

Accepted Answer

DNA denaturation and renaturation

Question 12

A researcher wants to identify a specific DNA sequence in a sample. Which technique would be most appropriate?

Accepted Answer

Nucleic acid hybridization

Question 13

Which of the following is a correct description of a kilobase (kb)?

Accepted Answer

1 kb = 1,000 base pairs

Question 14

Which of the following statements about base stacking in DNA is correct?

Accepted Answer

Base stacking stabilizes the helix through hydrophobic and van der Waals interactions

Question 15

Which of the following would most likely result in a higher DNA melting temperature ($$T_m$$)?

Accepted Answer

A DNA sequence with 70% GC content

Question 16

Which of the following is NOT a function of topoisomerases?

Accepted Answer

Catalyzing the formation of phosphodiester bonds during replication

Question 17

During DNA denaturation, which bonds are broken?

Accepted Answer

Hydrogen bonds between base pairs

Question 18

Which of the following best describes the major and minor grooves in DNA?

Accepted Answer

They are formed by the twisting of the two DNA strands around each other

Question 19

A scientist is studying a bacterial DNA molecule that is highly compact. Which structural feature is most likely responsible for this compaction?

Accepted Answer

Extensive supercoiling

Question 20

Which of the following is true regarding the number of nucleotide pairs per complete turn in the Watson-Crick DNA double helix?

Accepted Answer

There are 10 nucleotide pairs per turn

The Structural Basis of Cellular Information: DNA, Chromosomes, and the Nucleus

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