Question 1

Which structural feature of DNA ensures that the distance between the two sugar-phosphate backbones remains constant throughout the molecule?

Accepted Answer

The alternating arrangement of purines and pyrimidines on each strand

Question 2

According to Chargaff’s rules, if a DNA sample contains 23% guanine, what percentage of the nucleotides will be cytosine?

Accepted Answer

23%

Question 3

Which of the following best describes the directionality of DNA strands?

Accepted Answer

The two strands run anti-parallel, one from 5' to 3' and the other from 3' to 5'

Question 4

A sample of DNA from Sarcina lutea contains 13.4% adenine. According to Chargaff’s rules, what is the approximate percentage of thymine?

Accepted Answer

12.4%

Question 5

Which of the following equations correctly represents the relationship between base pairs in double-stranded DNA?

Accepted Answer

$$A + G = T + C$$

Question 6

What is the significance of the X-ray diffraction pattern produced by DNA fibers, as seen in Franklin’s photograph?

Accepted Answer

It provided evidence for the helical structure of DNA

Question 7

If cytosine makes up 32% of the nucleotides in a DNA sample, what percentage of the nucleotides will be guanine?

Accepted Answer

32%

Question 8

Which of the following statements about the sugar-phosphate backbone of DNA is correct?

Accepted Answer

It is hydrophilic and interacts with the polar environment

Question 9

In the DNA double helix, which type of bond holds the two strands together?

Accepted Answer

Hydrogen bonds between complementary bases

Question 10

Which of the following is a real-world application of Chargaff’s rules in forensic science?

Accepted Answer

Determining species identity from DNA base composition

Question 11

If a DNA molecule has 30% adenine, what is the percentage of thymine and what is the combined percentage of guanine and cytosine?

Accepted Answer

Thymine: 30%, Guanine + Cytosine: 40%

Question 12

Which of the following best explains why the base composition of DNA varies between species?

Accepted Answer

Different species have unique genetic codes and evolutionary histories

Question 13

What is the diameter of the DNA double helix?

Accepted Answer

$$2\ 	ext{nm}$$

Question 14

How many hydrogen bonds are formed between guanine and cytosine in DNA?

Accepted Answer

$$3$$

Question 15

Which of the following is NOT a component of a DNA nucleotide?

Accepted Answer

Ribose sugar

Question 16

A DNA molecule is composed of two strands. If one strand has the sequence 5'-AGTC-3', what is the sequence of the complementary strand?

Accepted Answer

3'-TCAG-5'

Question 17

Which scientist’s work was critical in providing the X-ray diffraction evidence for the helical structure of DNA?

Accepted Answer

Rosalind Franklin

Question 18

What is the distance between adjacent base pairs in the DNA double helix?

Accepted Answer

$$0.34\ 	ext{nm}$$

Question 19

Which of the following best describes the central core of the DNA double helix?

Accepted Answer

It consists of paired nitrogenous bases held together by hydrogen bonds

Question 20

Which of the following is a correct statement about the pairing of bases in DNA?

Accepted Answer

A pairs with T and G pairs with C

DNA Structure and Chargaff’s Rules: Foundations of Molecular Genetics

Study Guide - Practice Questions