Question 1

Which structural feature is responsible for the greater chemical stability of DNA compared to RNA?

Accepted Answer

DNA lacks a 2'-OH group on the deoxyribose sugar.

Question 2

In the Watson-Crick model of DNA, how many hydrogen bonds are formed between guanine and cytosine?

Accepted Answer

$$3$$

Question 3

Which of the following statements correctly describes the polarity of a nucleic acid strand?

Accepted Answer

The strand has a 5' phosphate group and a 3' hydroxyl group.

Question 4

Which base is found in RNA but not in DNA?

Accepted Answer

Uracil

Question 5

A DNA strand has the sequence $$5'\ \mathrm{ATCGGCA}\ \ 3'. $$What is the sequence of its complementary strand?

Accepted Answer

$$3'\ \mathrm{TAGCCGT}\ \ 5'$$

Question 6

Which of the following correctly describes the linkage between nucleotides in DNA and RNA?

Accepted Answer

A phosphodiester bond between the 3' hydroxyl of one sugar and the 5' phosphate of the next

Question 7

Which form of DNA is most commonly found under physiological conditions in cells?

Accepted Answer

B-DNA

Question 8

What is the diameter of B-form DNA?

Accepted Answer

$$20\ \mathrm{\AA}$$

Question 9

Which statement best explains why RNA is more susceptible to alkaline hydrolysis than DNA?

Accepted Answer

RNA has a 2'-OH group that can participate in base-catalyzed cleavage of the backbone.

Question 10

Which of the following is a purine base found in nucleic acids?

Accepted Answer

Adenine

Question 11

What is the sugar pucker conformation in B-form DNA?

Accepted Answer

C-2' endo

Question 12

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 13

Which of the following conditions favors the formation of Z-DNA?

Accepted Answer

Alternating purine-pyrimidine sequences and high salt concentration

Question 14

What is the rise per base pair in B-form DNA?

Accepted Answer

$$3.4\ \mathrm{\AA}$$

Question 15

Which of the following is true about the major and minor grooves in B-form DNA?

Accepted Answer

The major groove is wide and deep, while the minor groove is narrow and deep.

Question 16

Which bond connects the base to the sugar in a nucleotide?

Accepted Answer

$$\beta-1$$'-N-glycosidic bond

Question 17

How many atoms are present in the ring system of a pyrimidine base?

Accepted Answer

$$6$$

Question 18

What charge does each phosphate group in the DNA/RNA backbone carry at physiological pH?

Accepted Answer

$$-1$$

Question 19

Which of the following is a correct description of the A-form DNA helix compared to B-form?

Accepted Answer

A-form DNA has a wider diameter and fewer base pairs per turn than B-form.

Question 20

Which of the following best explains the importance of DNA's chemical stability for its biological function?

Accepted Answer

DNA's stability ensures long-term storage and transmission of genetic information.

Nucleic Acid Structure: DNA and RNA – Composition, Linkage, and Helical Forms

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