Question 1

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

Accepted Answer

The two strands run antiparallel to each other; one runs 5' to 3', the other 3' to 5'.

Question 2

Which of the following is NOT a component of a DNA nucleotide?

Accepted Answer

A ribose sugar

Question 3

What type of bond forms between complementary nitrogenous bases in the DNA double helix?

Accepted Answer

Hydrogen bonds

Question 4

If a segment of one DNA strand has the sequence 5'-ATCG-3', what is the sequence of the complementary strand (written 5' to 3')?

Accepted Answer

5'-CGAT-3'

Question 5

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

Accepted Answer

Adenine pairs with thymine via two hydrogen bonds.

Question 6

Which form of DNA is most commonly found in living cells and has a right-handed helix?

Accepted Answer

B-DNA

Question 7

What is the main functional significance of the major and minor grooves in the DNA double helix?

Accepted Answer

They provide binding sites for DNA-binding proteins and regulatory factors.

Question 8

Which of the following best explains why the two strands of DNA are antiparallel?

Accepted Answer

It enables complementary base pairing and proper alignment of hydrogen bonds between bases.

Question 9

A DNA molecule is 340 base pairs long. Approximately how many complete turns of the double helix does it contain? (Assume 10 base pairs per turn.)

Accepted Answer

$$340 \div 10 = 34$$ turns

Question 10

Which of the following best describes the difference between purines and pyrimidines in DNA?

Accepted Answer

Purines have a double ring structure, while pyrimidines have a single ring.

Question 11

Which of the following is a correct pairing of a purine and a pyrimidine in DNA?

Accepted Answer

Adenine and thymine

Question 12

What would happen if DNA base pairing occurred between two purines or two pyrimidines?

Accepted Answer

The DNA helix would have irregular diameter, disrupting the structure.

Question 13

Which of the following best explains the stability of the DNA double helix?

Accepted Answer

Hydrogen bonds between base pairs and base stacking interactions between adjacent bases.

Question 14

Which of the following statements about Z-DNA is correct?

Accepted Answer

Z-DNA has a left-handed helix and a zigzag sugar-phosphate backbone.

Question 15

A mutation causes a DNA segment to have the sequence 5'-GCTTAC-3'. What is the complementary sequence (written 3' to 5')?

Accepted Answer

3'-CGAATG-5'

Question 16

Which of the following best describes the role of DNA polymerase during DNA synthesis?

Accepted Answer

It adds nucleotides to the growing DNA strand by forming phosphodiester bonds.

Question 17

Why is the presence of both major and minor grooves in DNA important for cellular function?

Accepted Answer

They provide access for proteins to interact with specific DNA sequences.

Question 18

Which of the following equations correctly represents the number of hydrogen bonds between guanine and cytosine in DNA?

Accepted Answer

$$	ext{G} \equiv 	ext{C}$$: 3 	ext{ hydrogen bonds}$

Question 19

A DNA molecule is found to have 30% adenine. According to Chargaff's rules, what percentage of guanine would you expect to find?

Accepted Answer

20%

Question 20

Which of the following best explains why DNA is more stable than RNA under cellular conditions?

Accepted Answer

DNA contains deoxyribose, which lacks a 2' hydroxyl group, making it less susceptible to hydrolysis.

The DNA Double Helix: Structure, Components, and Forms

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