Question 1

Which of the following experiments provided the first direct evidence that DNA, and not protein, is the genetic material responsible for heredity?

Accepted Answer

The Hershey-Chase experiment using bacteriophage T2 and isotope labeling

Question 2

A sample of DNA is found to contain 15% thymine. According to Chargaff’s rules, what percentage of guanine would you expect to find in this DNA?

Accepted Answer

$$35\%$$

Question 3

Which structural feature distinguishes RNA from DNA at the molecular level?

Accepted Answer

RNA contains a hydroxyl group at the 2' carbon of its ribose sugar, while DNA has a hydrogen at this position.

Question 4

In the classic Griffith experiment with Streptococcus pneumoniae, what was the key observation that suggested a 'transforming principle'?

Accepted Answer

Mice injected with live type R and heat-killed type S bacteria died, and live type S bacteria were recovered.

Question 5

Which of the following best describes the directionality of a DNA strand?

Accepted Answer

The strand has a 5' phosphate group at one end and a 3' hydroxyl group at the other end.

Question 6

Which of the following base pairs is stabilized by three hydrogen bonds in the DNA double helix?

Accepted Answer

Guanine and cytosine

Question 7

A scientist isolates a nucleic acid and finds that it contains uracil, is single-stranded, and has ribose as its sugar. What is the identity of this nucleic acid?

Accepted Answer

RNA

Question 8

Which of the following is NOT a property required of the genetic material?

Accepted Answer

It must catalyze metabolic reactions.

Question 9

What is the function of the major and minor grooves in the DNA double helix?

Accepted Answer

They provide access for proteins to interact with the bases for processes such as replication and transcription.

Question 10

Which of the following best explains why DNA absorbs ultraviolet light most strongly at 260 nm?

Accepted Answer

The aromatic bases in DNA have maximum absorbance at this wavelength.

Question 11

If a DNA strand has the sequence 5'–AGTCTTTA–3', what is the sequence and orientation of its complementary strand?

Accepted Answer

3'–TCAGAAAT–5'

Question 12

Which of the following statements about B-DNA and Z-DNA is correct?

Accepted Answer

B-DNA is the predominant form in living cells, while Z-DNA forms under certain conditions and has a zigzag backbone.

Question 13

Which of the following best describes the structure of a nucleotide found in DNA?

Accepted Answer

A phosphate group, a deoxyribose sugar, and a nitrogenous base

Question 14

Which of the following is a correct feature of the Watson and Crick model of DNA?

Accepted Answer

The two strands are antiparallel and held together by hydrogen bonds between complementary bases.

Question 15

Which of the following best explains the result of the Hershey-Chase experiment using $$^{32}P$$ and $$^{35}S$$ isotopes?

Accepted Answer

$$^{32}P$$ labeled DNA entered the bacterial cells, while $$^{35}S$$ labeled protein did not, indicating DNA is the genetic material.

Question 16

Which of the following is a real-life application of understanding the structure of DNA?

Accepted Answer

Forensic DNA fingerprinting to identify individuals in criminal investigations

Question 17

Which of the following best describes the phosphodiester bond in nucleic acids?

Accepted Answer

It links the 5' phosphate of one nucleotide to the 3' hydroxyl of the next nucleotide.

Question 18

Which of the following is a function of transfer RNA (tRNA) in the cell?

Accepted Answer

It carries amino acids to the ribosome during protein synthesis.

Question 19

Which of the following best explains why DNA, and not protein, is considered the genetic material in most organisms?

Accepted Answer

DNA fulfills all four criteria for genetic material: information, transmission, replication, and variation.

Structure of DNA and RNA: Foundations of Genetic Material

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