Question 1

Which of the following correctly describes the three components of a nucleotide found in DNA?

Accepted Answer

A nitrogenous base, a five-carbon sugar, and a phosphate group

Question 2

Which nitrogenous base is found in RNA but not in DNA?

Accepted Answer

Uracil

Question 3

What type of bond connects nucleotides together in a DNA strand?

Accepted Answer

Phosphodiester bond

Question 4

Which of the following best explains why DNA is negatively charged at physiological pH?

Accepted Answer

The phosphate groups in the backbone carry negative charges

Question 5

In the double helix structure of DNA, which base pairs with guanine?

Accepted Answer

Cytosine

Question 6

Which statement about the directionality of DNA strands is correct?

Accepted Answer

The two strands are antiparallel, one runs 5' to 3' and the other 3' to 5'

Question 7

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

Accepted Answer

Adenine

Question 8

What is the main function of topoisomerases in cells?

Accepted Answer

To maintain the level of DNA supercoiling by introducing or removing twists

Question 9

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

Accepted Answer

A nucleoside contains a nitrogenous base and a five-carbon sugar; a nucleotide contains a base, sugar, and phosphate group

Question 10

Which of the following equations correctly represents the number of base pairs per complete turn in B-form DNA?

Accepted Answer

$$10.5 \ 	ext{bp/turn}$$

Question 11

During DNA denaturation, which bonds are broken?

Accepted Answer

Hydrogen bonds between complementary bases

Question 12

Which of the following is a consequence of DNA supercoiling in cells?

Accepted Answer

DNA takes up less space, allowing efficient packaging in the nucleus

Question 13

If a DNA molecule is underwound, what type of supercoiling is most likely to occur?

Accepted Answer

Negative supercoiling

Question 14

Which of the following best describes the role of hydrogen bonding in the DNA double helix?

Accepted Answer

Hydrogen bonds form between complementary nitrogenous bases, stabilizing the double helix

Question 15

Which of the following is true regarding the major and minor grooves of DNA?

Accepted Answer

They result from the geometry of the base pairs and play a role in protein-DNA interactions

Question 16

A scientist isolates a nucleic acid and finds it contains uracil, ribose, and a phosphate group. What type of molecule is this?

Accepted Answer

RNA

Question 17

Which of the following is the correct chemical formula for a phosphate group as found in nucleotides?

Accepted Answer

$$\mathrm{PO_4$^{3-}}$$

Question 18

Which process requires the action of topoisomerases to relieve tension in the DNA molecule?

Accepted Answer

Transcription and replication

Question 19

Which of the following best explains why base stacking contributes to the stability of the DNA double helix?

Accepted Answer

Base stacking involves hydrophobic interactions that minimize water exposure

Question 20

Which of the following is the correct order of events in the formation of a DNA chain?

Accepted Answer

Nucleoside formation, addition of phosphate group, polymerization via phosphodiester bonds

The Structure of DNA: Nucleic Acids, Nucleotides, and DNA Organization

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