Question 1

Which experimental result from Frederick Griffith's work provided the first evidence that DNA could transfer genetic information between organisms?

Accepted Answer

Mice injected with a mixture of heat-killed S cells and living R cells died, and living S cells were recovered from their blood.

Question 2

In the Hershey-Chase experiment, which molecule was labeled with radioactive phosphorus ($$^{32}P) $$and why?

Accepted Answer

DNA, because phosphorus is found in the phosphate backbone of DNA.

Question 3

What conclusion did Hershey and Chase draw from their experiment using bacteriophages labeled with $$^{35}S$$ and $$^{32}P$$?

Accepted Answer

DNA is the genetic material because only radioactive DNA entered the bacterial cell and directed the production of new phages.

Question 4

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

Accepted Answer

A phosphate group, a pentose sugar (deoxyribose), and a nitrogenous base.

Question 5

According to Chargaff’s rules, if a DNA sample from a new organism contains 22% adenine, what percentage of thymine would you expect to find?

Accepted Answer

$$22\%$$

Question 6

Why does pairing a purine with a pyrimidine maintain a uniform width in the DNA double helix?

Accepted Answer

Purines are larger than pyrimidines, so pairing one of each keeps the helix width consistent with X-ray data.

Question 7

Which feature of DNA did Rosalind Franklin’s X-ray diffraction photograph reveal?

Accepted Answer

That DNA is a double helix with a regular, repeating structure.

Question 8

If a DNA strand has the sequence 5'-GAATTC-3', what is the complementary strand’s sequence?

Accepted Answer

3'-CTTAAG-5'

Question 9

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

Accepted Answer

It is held together by covalent phosphodiester bonds between the 3' carbon of one sugar and the 5' phosphate of the next.

Question 10

A scientist isolates DNA from a sea urchin and finds it contains 17.7% guanine. According to Chargaff’s rules, what percentage of cytosine should be present?

Accepted Answer

$$17.3\%$$

Question 11

Which of the following best explains why proteins were originally considered better candidates than DNA for the genetic material?

Accepted Answer

Proteins have greater heterogeneity and specificity of function than DNA.

Question 12

Which real-world application relies on the specificity of base pairing in DNA?

Accepted Answer

DNA fingerprinting in forensic science.

Question 13

What would happen in the Hershey-Chase experiment if proteins, not DNA, were the genetic material?

Accepted Answer

Radioactive sulfur ($$^{35}S) $$would be found inside the bacterial cells after infection.

Question 14

Which of the following is a direct result of the antiparallel arrangement of DNA strands?

Accepted Answer

The 5' end of one strand is opposite the 3' end of the other strand.

Question 15

Which chemical property allows adenine to pair specifically with thymine in DNA?

Accepted Answer

Adenine forms two hydrogen bonds with thymine.

Question 16

A mutation causes a DNA strand to have two purines paired together. What is the likely effect on the DNA double helix?

Accepted Answer

The helix will bulge at that point, disrupting the uniform width.

Question 17

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

Accepted Answer

A ribose sugar

Question 18

Why was the discovery of the double helix structure of DNA so important for understanding heredity?

Accepted Answer

It revealed how DNA could be copied and passed on to the next generation.

DNA as the Genetic Material: Historical Experiments and Molecular Structure

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