Question 1

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

Accepted Answer

DNA contains a deoxyribose sugar, which lacks a hydroxyl group at the 2' carbon.

Question 2

A researcher isolates a nucleic acid and finds that it contains the bases adenine, guanine, cytosine, and uracil, as well as a sugar with a hydroxyl group at the 2' carbon. What type of molecule is this?

Accepted Answer

RNA

Question 3

Which of the following statements about phosphodiester bonds in nucleic acids is correct?

Accepted Answer

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

Question 4

A DNA molecule is analyzed and found to contain 28% cytosine. According to Chargaff’s rules, what percentage of the molecule is adenine?

Accepted Answer

$$22\%$$

Question 5

Which of the following is a purine base found in both DNA and RNA?

Accepted Answer

Adenine

Question 6

What is the significance of the major groove in B-DNA?

Accepted Answer

It provides a wider region for protein binding and sequence recognition.

Question 7

Which of the following best describes the handedness and base pairs per turn of B-DNA under physiological conditions?

Accepted Answer

Right-handed helix with 10 base pairs per turn

Question 8

A mutation replaces a guanine with an adenine in a DNA strand. Which of the following changes in hydrogen bonding would occur at this site?

Accepted Answer

The site would now form two hydrogen bonds instead of three.

Question 9

Which of the following is NOT a feature of Z-DNA?

Accepted Answer

It forms under high humidity and physiological conditions.

Question 10

Which of the following best explains why complementary base pairing is essential for DNA replication?

Accepted Answer

It ensures that each new strand is an accurate copy of the template strand.

Question 11

A scientist is studying a nucleic acid with the following characteristics: single-stranded, contains uracil, and has a ribose sugar. Which molecule is being studied?

Accepted Answer

RNA

Question 12

Which of the following statements about the sugar-phosphate backbone of DNA is correct?

Accepted Answer

It gives DNA its directionality from 5' to 3'.

Question 13

Which of the following best describes the difference between A-DNA and B-DNA?

Accepted Answer

A-DNA forms under low humidity and is more compact than B-DNA.

Question 14

Which of the following is a correct statement about the base composition of DNA according to Chargaff’s rules?

Accepted Answer

$$\%A = \%T$$

Question 15

Which of the following best describes the role of nucleotide triphosphates in nucleic acid synthesis?

Accepted Answer

They serve as the energy source and building blocks for nucleic acid polymerization.

Question 16

A DNA molecule is 20% guanine. What is the percentage of thymine in this molecule?

Accepted Answer

$$30\%$$

Question 17

Which of the following statements about the minor groove of DNA is correct?

Accepted Answer

It provides less sequence-specific information for protein binding.

Question 18

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

Accepted Answer

A carboxyl group

Question 19

Which of the following best describes the directionality of DNA synthesis?

Accepted Answer

DNA is synthesized in the 5' to 3' direction.

Molecular Structure of DNA: Composition, Structure, and Forms

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