Question 1

Which experiment provided the first evidence that DNA could transfer genetic information between organisms, and what was the key observation?

Accepted Answer

Griffith's transformation experiment; observed that non-virulent bacteria became virulent when mixed with heat-killed virulent bacteria.

Question 2

In the Hershey-Chase experiment, which isotope was used to label DNA, and what was the conclusion regarding the genetic material of phages?

Accepted Answer

$$^{32}\mathrm{P}$$; DNA is the genetic material.

Question 3

According to Chargaff’s rules, if a DNA sample contains 30% adenine, what percentage of guanine would you expect?

Accepted Answer

20%

Question 4

Which feature of Rosalind Franklin’s X-ray diffraction image was critical in deducing the double helical structure of DNA?

Accepted Answer

The cross-shaped pattern indicating a helical structure.

Question 5

What is the chemical difference between the sugars in DNA and RNA?

Accepted Answer

DNA contains deoxyribose (2' C has H); RNA contains ribose (2' C has OH).

Question 6

Which of the following best describes the directionality of DNA strands in the double helix?

Accepted Answer

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

Question 7

Which interaction is NOT a major contributor to the stability of the DNA double helix?

Accepted Answer

Covalent bonds between base pairs.

Question 8

A DNA molecule is found to have 22% cytosine. According to Chargaff’s rules, what is the expected percentage of thymine?

Accepted Answer

28%

Question 9

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

Accepted Answer

B form

Question 10

What is the significance of palindromic sequences in DNA?

Accepted Answer

They are sites for restriction enzyme cleavage and can form hairpin or cruciform structures.

Question 11

Which of the following best explains the semi-conservative model of DNA replication?

Accepted Answer

Each daughter DNA molecule consists of one parental and one new strand.

Question 12

Which of the following is a pyrimidine base found in DNA?

Accepted Answer

Cytosine

Question 13

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

Accepted Answer

$$3.4\ \mathrm{\AA}$$

Question 14

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

Accepted Answer

It is hydrophilic and found on the outside of the helix.

Question 15

If a DNA sequence is 5'-GATATC-3', what is the sequence of its complementary strand?

Accepted Answer

3'-CTATAG-5'

Question 16

Which of the following best describes the relationship between DNA, mRNA, and protein sequences?

Accepted Answer

The 5'-3' order of nucleotides in DNA is copied into mRNA, which determines the amino acid sequence of proteins.

Question 17

Which of the following is NOT a feature of the Watson-Crick model of DNA?

Accepted Answer

Left-handed double helix

Question 18

Which of the following best explains why DNA is considered an 'acid'?

Accepted Answer

Its phosphate groups are negatively charged.

Question 19

Which DNA form is characterized by a left-handed helix and is often found in regions with alternating CG sequences?

Accepted Answer

Z form

Question 20

Which of the following is a correct description of a phosphodiester bond in nucleic acids?

Accepted Answer

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

DNA: The Genetic Material – Structure, Evidence, and Function

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