$$n_{AT} \times 2 + n_{GC} \times 3$$

Question 1

Which of the following statements correctly describes the difference between the A and B forms of double-stranded DNA?

Accepted Answer

B form DNA is found in high humidity environments, while A form DNA is found in low humidity.

Question 2

What is the primary reason that single strands of DNA are held together in double-stranded DNA?

Accepted Answer

Hydrogen bonds and hydrophobic stacking forces.

Question 3

Which form of DNA is most likely to be found in dehydrated samples or in the presence of certain solvents?

Accepted Answer

A form

Question 4

The stacking forces that stabilize the DNA double helix primarily arise from:

Accepted Answer

The hydrophobic effect of the nitrogenous bases stacking in the B form.

Question 5

Which of the following is TRUE regarding B-Z junctions in DNA?

Accepted Answer

They are formed when the helix switches between the B and Z forms.

Question 6

Why are regulatory sequences easier to identify in Z form DNA compared to B form DNA?

Accepted Answer

Z form DNA has a unique shape that makes regulatory sequences more distinguishable.

Question 7

Which of the following best describes the orientation of the DNA helix in the Z form?

Accepted Answer

It is a left-handed helix.

Question 8

If a DNA sample is exposed to high humidity, which form is it most likely to adopt?

Accepted Answer

B form

Question 9

Which of the following equations best represents the number of hydrogen bonds between base pairs in double-stranded DNA?

Accepted Answer

$$n_{AT} 	imes 2 + n_{GC} 	imes 3$$

Question 10

A mutation causes a segment of DNA to switch from B form to Z form. What is the most likely effect on gene regulation?

Accepted Answer

Regulatory sequences may become easier to identify due to the altered shape.

Question 11

Which of the following is NOT a characteristic of B form DNA?

Accepted Answer

It is stabilized primarily by ionic bonds.

Question 12

Which of the following scenarios would most likely result in the formation of A form DNA?

Accepted Answer

DNA in a dehydrated environment.

Question 13

What is the main structural difference between A, B, and Z forms of DNA?

Accepted Answer

The handedness and compactness of the helix.

Question 14

Which of the following statements about DNA stacking forces is correct?

Accepted Answer

Stacking forces are due to hydrophobic interactions between bases.

Question 15

A researcher observes a DNA segment switching helix direction. What is the most likely explanation?

Accepted Answer

The DNA is forming a B-Z junction.

Question 16

Which of the following forms of DNA is most likely to contain regulatory sequences that are easy to identify?

Accepted Answer

Z form

Question 17

Which of the following is a correct statement about the B-Z junction in DNA?

Accepted Answer

It is a region where the DNA helix switches from B form to Z form.

Question 18

Which of the following best explains why the stacking forces are stronger in B form DNA?

Accepted Answer

The bases are stacked more closely due to the squashed nature of the B form.

Question 19

Which of the following forms of DNA is most likely to be found in double-stranded RNA?

Accepted Answer

A form

Question 20

Which of the following is a consequence of the hydrophobic stacking of bases in DNA?

Accepted Answer

Increased stability of the double helix.

Nucleic Acids: Structure and Forms of DNA

Study Guide - Practice Questions