Question 1

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

Accepted Answer

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

Question 2

A researcher is measuring the concentration of a DNA solution using UV absorbance. Which property of nucleic acids allows this method to work, and at what wavelength is the absorbance typically measured?

Accepted Answer

The aromaticity of nitrogenous bases allows strong absorbance at $$260\ \mathrm{nm}.$$

Question 3

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

Accepted Answer

A nucleoside consists of a nitrogenous base and a sugar, while a nucleotide also contains one or more phosphate groups.

Question 4

Which of the following is a correct pairing of a purine and a pyrimidine in double-stranded DNA, and how many hydrogen bonds are formed between them?

Accepted Answer

Guanine and cytosine; three hydrogen bonds

Question 5

A dog is brought to a veterinarian after eating a large amount of chocolate. Theobromine toxicity is suspected. Which of the following best explains why theobromine is toxic to dogs but less so to humans?

Accepted Answer

Dogs metabolize theobromine much more slowly than humans, leading to toxic accumulation.

Question 6

Which of the following best describes the main stabilizing force in the double helix structure of DNA?

Accepted Answer

Base stacking interactions (van der Waals forces) between adjacent bases

Question 7

Which of the following statements about the directionality of nucleic acids is correct?

Accepted Answer

Nucleic acids are synthesized and read from the $$5' to$$ $$3'$$ direction.

Question 8

Which of the following best explains why proteins that regulate gene expression often bind to the major groove of DNA?

Accepted Answer

The major groove exposes more functional groups for sequence-specific recognition.

Question 9

Which of the following is a correct description of the chemical linkage that joins nucleotides in a nucleic acid strand?

Accepted Answer

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

Question 10

A DNA sample is heated to $$95^\circ \mathrm{C}$$, causing the two strands to separate. Which of the following best explains what happens when the sample is slowly cooled back to room temperature?

Accepted Answer

The complementary strands re-anneal due to hydrogen bonding and base stacking interactions.

Question 11

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

Accepted Answer

B-form DNA is a right-handed helix, while Z-form DNA is a left-handed helix.

Question 12

Which of the following statements about the hydrophobic effect in DNA structure is correct?

Accepted Answer

The hydrophobic bases are stacked in the interior of the helix, shielded from water, while the hydrophilic backbone is exposed.

Question 13

A mutation replaces a cytosine with a thymine in a DNA strand. Which of the following changes in base pairing would you expect as a result?

Accepted Answer

The mutated thymine will pair with adenine instead of guanine.

Question 14

Which of the following best explains why caffeine can act as a stimulant in the human body?

Accepted Answer

Caffeine is a structural analogue of adenosine and blocks adenosine receptors, reducing sleepiness.

Question 15

Which of the following is a property shared by all nitrogenous bases found in nucleic acids?

Accepted Answer

They are aromatic and planar, allowing stacking interactions.

Question 16

A DNA molecule has the sequence $$5'	ext{-}AGTC-3'. $$What is the sequence of the complementary strand, including directionality?

Accepted Answer

$$3'	ext{-}TCAG-5'$$

Question 17

Which of the following best describes the role of phosphoanhydride bonds in nucleotides such as ATP?

Accepted Answer

They store and release energy used to drive cellular reactions.

Question 18

Which of the following is a correct statement about the net charge of nucleic acids at physiological pH?

Accepted Answer

Nucleic acids have a net negative charge due to the phosphate backbone.

Question 19

Which of the following best explains why the double helix of DNA is right-handed in the B-form?

Accepted Answer

The geometry of the sugar-phosphate backbone and base pairing favors a right-handed twist.

Structure and Properties of Nucleotides and Nucleic Acids

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