Question 1

Which of the following best describes the difference between a nucleoside and a nucleotide?

Accepted Answer

A nucleoside contains a nitrogenous base and a pentose sugar, while a nucleotide also includes a phosphate group.

Question 2

Which of the following statements about the structure of DNA is correct?

Accepted Answer

The two strands of DNA are antiparallel, with one running 5' to 3' and the other 3' to 5'.

Question 3

Which base pairing is stabilized by three hydrogen bonds in DNA?

Accepted Answer

Guanine and cytosine

Question 4

What is the significance of the 2' carbon in the pentose sugar of DNA compared to RNA?

Accepted Answer

DNA has a hydrogen at the 2' carbon, while RNA has a hydroxyl group at the same position.

Question 5

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

Accepted Answer

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

Question 6

A DNA molecule has the following sequence on one strand: 5'-ATGCCGTA-3'. What is the complementary sequence on the other strand?

Accepted Answer

3'-TACGGCAT-5'

Question 7

Which of the following is a pyrimidine found in DNA but not in RNA?

Accepted Answer

Thymine

Question 8

What type of bond links two nucleotides together in a DNA strand?

Accepted Answer

Phosphodiester bond

Question 9

According to Chargaff's rules, if a DNA sample from a species contains 30% adenine, what percentage of guanine would you expect to find?

Accepted Answer

20%

Question 10

Which experimental evidence was crucial in determining the helical structure of DNA?

Accepted Answer

X-ray diffraction studies by Rosalind Franklin

Question 11

If a mutation causes a cytosine in DNA to be replaced by a thymine, what type of base pairing change would occur?

Accepted Answer

A G-C pair (3 H-bonds) would be replaced by an A-T pair (2 H-bonds), reducing stability.

Question 12

Which of the following best describes the polarity of a DNA strand?

Accepted Answer

The 5' end has a free phosphate group, and the 3' end has a free hydroxyl group.

Question 13

Which of the following is a correct feature of the B-DNA double helix?

Accepted Answer

There are 10 base pairs per complete turn of the helix.

Question 14

Which of the following best explains why the major and minor grooves form in the DNA double helix?

Accepted Answer

The sugar-phosphate backbones are not equally spaced around the helix.

Question 15

A scientist isolates a nucleic acid and finds it contains uracil, ribose, and is single-stranded. What is the identity of this molecule?

Accepted Answer

RNA

Question 16

Which of the following equations correctly represents the relationship between the percentages of bases in double-stranded DNA according to Chargaff's rules?

Accepted Answer

$$\%A = \%T$$ and $$\%G = \%C$$

Question 17

Which of the following best describes the role of phosphodiester bonds in DNA?

Accepted Answer

They form the covalent linkage between the 5' phosphate of one nucleotide and the 3' hydroxyl of the next.

Question 18

If the distance between two adjacent base pairs in DNA is 0.34 nm, what is the length of one complete turn of the helix?

Accepted Answer

$$0.34\ \mathrm{nm} 	imes 10 = 3.4\ \mathrm{nm}$$

Question 19

A patient is diagnosed with a genetic disorder caused by instability in their DNA. Which of the following molecular features is most likely compromised?

Accepted Answer

The integrity of the phosphodiester bonds in the DNA backbone

DNA Structure: Nucleotides, Double Helix, and Chemical Composition

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