Question 1

Which of the following correctly identifies the three main components of a nucleotide as shown in the diagram?

Accepted Answer

Phosphate group, pentose sugar, nitrogenous base

Question 2

In the nucleotide diagram, which carbon of the sugar is directly attached to the phosphate group?

Accepted Answer

5' carbon

Question 3

Which group is found at the 3' end of a DNA strand and is essential for chain elongation during DNA replication?

Accepted Answer

Hydroxyl group ($$-OH)$$

Question 4

If a DNA molecule contains 30% adenine, what percentage of guanine does it contain?

Accepted Answer

$$20\%$$

Question 5

According to Chargaff’s rules, which of the following equations correctly represents the relationship between the bases in double-stranded DNA?

Accepted Answer

$$[A] = [T]$$ and $$[G] = [C]$$

Question 6

A scientist isolates a nucleotide with a pentose sugar that lacks an oxygen atom at the 2' position. Is this nucleotide from DNA or RNA?

Accepted Answer

DNA

Question 7

Which of the following best explains why the percentage of adenine always equals the percentage of thymine in double-stranded DNA?

Accepted Answer

Adenine forms two hydrogen bonds with thymine, creating base pairs

Question 8

A DNA sample is found to have 18% cytosine. What is the percentage of thymine in this sample?

Accepted Answer

$$32\%$$

Question 9

Which of the following statements about the structure of DNA is correct?

Accepted Answer

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

Question 10

A mutation changes a nucleotide in DNA so that the 3' hydroxyl group is missing. What is the most likely consequence during DNA replication?

Accepted Answer

DNA polymerase cannot add new nucleotides, halting replication

Question 11

Which of the following best describes the difference between a nucleotide found in DNA and one found in RNA?

Accepted Answer

DNA nucleotides contain deoxyribose; RNA nucleotides contain ribose

Question 12

A researcher finds a nucleic acid with the following base composition: 22% adenine, 28% thymine, 27% guanine, and 23% cytosine. What can you infer about this nucleic acid?

Accepted Answer

It is likely single-stranded

Question 13

Which of the following is a correct representation of the directionality of a DNA strand?

Accepted Answer

$$5' \rightarrow 3'$$

Question 14

If a DNA molecule is composed of 35% guanine, what is the percentage of thymine?

Accepted Answer

$$15\%$$

Question 15

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

Accepted Answer

DNA lacks a 2' hydroxyl group, making it less susceptible to hydrolysis

DNA Structure: Nucleotides and Chargaff’s Rules

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