Question 1

Which of the following best explains why DNA contains thymine instead of uracil?

Accepted Answer

Cytosine can spontaneously deaminate to form uracil, so using thymine (5-methyl-U) allows repair enzymes to distinguish natural U from mutant U.

Question 2

Which statement correctly describes the difference between nucleosides and nucleotides?

Accepted Answer

Nucleotides contain a base, a sugar, and at least one phosphate group, while nucleosides lack the phosphate group.

Question 3

A DNA sample is analyzed and found to have 30% adenine. According to Chargaff's rules, what is the expected percentage of guanine?

Accepted Answer

20%

Question 4

Which of the following is a correct representation of the Beer-Lambert Law used in UV absorbance measurements?

Accepted Answer

$$A = \varepsilon c l$$

Question 5

Which feature of RNA makes it more susceptible to alkaline hydrolysis compared to DNA?

Accepted Answer

Presence of a 2'-OH group on the ribose sugar

Question 6

A researcher measures the absorbance of a nucleic acid sample at 260 nm and 280 nm. The ratio $$A_{260}/A_{280} is $$found to be 0.5. What does this indicate about the sample?

Accepted Answer

The sample is primarily protein with little nucleic acid contamination.

Question 7

Which of the following statements about DNA denaturation is TRUE?

Accepted Answer

DNA denaturation can be promoted by heat, alkaline pH, and electrostatic repulsion between phosphate groups.

Question 8

Which of the following is a palindromic DNA sequence?

Accepted Answer

5'-GAATTC-3'

Question 9

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

Accepted Answer

B-form DNA

Question 10

What is the net charge of a nucleotide in DNA at physiological pH ($$pH \approx 7.4$$)?

Accepted Answer

$$-1$$

Question 11

Which of the following is a function of adenosine as a nucleoside?

Accepted Answer

Serves as a local hormone (autacoid) influencing blood vessel dilation and sleep regulation

Question 12

Which statement best describes the role of ethidium bromide in DNA topology experiments?

Accepted Answer

Ethidium bromide intercalates between base pairs, unwinding the helix and promoting positive supercoiling.

Question 13

Which of the following is TRUE regarding the difference between ribose and deoxyribose?

Accepted Answer

Deoxyribose has a hydrogen at the 2' position, making DNA less susceptible to hydrolysis.

Question 14

Which of the following correctly matches the nucleotide with its nucleoside and base?

Accepted Answer

Cytidine 5'-monophosphate: nucleoside is cytidine, base is cytosine

Question 15

Which of the following is TRUE about the A-form helix?

Accepted Answer

It is the only structure formed by double-stranded RNA.

Question 16

Which of the following is a correct function of nucleoside 5'-triphosphates?

Accepted Answer

UTP drives carbohydrate metabolism.

Question 17

A mixture of nucleotides is separated by ion-exchange chromatography at pH 3.8. What is the expected net charge of AMP under these conditions?

Accepted Answer

$$-0.5$$

Question 18

Which of the following statements about restriction enzymes is TRUE?

Accepted Answer

Most restriction enzyme recognition sites are palindromic.

Question 19

Which of the following stabilizes the DNA double helix?

Accepted Answer

Hydrogen bonds between base pairs and base-pair stacking interactions

Chapter 4: Nucleic Acids – Structure, Properties, and Biological Functions

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