Question 1

Which of the following best explains why sulfur and phosphorus were chosen as radioactive labels in the Hershey-Chase experiment?

Accepted Answer

Sulfur is found in proteins but not DNA, and phosphorus is found in DNA but not proteins.

Question 2

A DNA molecule has the following base composition: 30% adenine, 20% guanine. According to Chargaff’s rules, what percentage of thymine and cytosine would you expect?

Accepted Answer

Thymine: 30%, Cytosine: 20%

Question 3

Which of the following statements about Rosalind Franklin’s X-ray crystallography findings is correct?

Accepted Answer

She provided evidence that DNA is a double helix with a consistent diameter.

Question 4

What type of chemical bond holds together the base pairs in a DNA double helix?

Accepted Answer

Hydrogen bonds

Question 5

Why must a purine always pair with a pyrimidine in the DNA double helix?

Accepted Answer

To ensure the DNA molecule has a uniform diameter

Question 6

Which of the following best describes the 5’ and 3’ ends of a DNA strand?

Accepted Answer

The 5’ end has a free phosphate group, and the 3’ end has a free -OH group.

Question 7

In the Meselson-Stahl experiment, after one round of DNA replication in light nitrogen, what was observed?

Accepted Answer

All DNA was of intermediate density (hybrid).

Question 8

Which of the following is NOT a difference between DNA and RNA?

Accepted Answer

DNA contains phosphate, RNA does not.

Question 9

A mature mRNA transcript differs from pre-mRNA in which of the following ways?

Accepted Answer

Mature mRNA has a poly-A tail and no introns.

Question 10

What does it mean that the genetic code is 'degenerate' or 'redundant'?

Accepted Answer

Multiple codons can code for the same amino acid.

Question 11

Which enzyme is responsible for synthesizing the RNA primer during DNA replication?

Accepted Answer

Primase

Question 12

A mutation changes a codon from UAU (tyrosine) to UAA (stop codon). What type of mutation is this?

Accepted Answer

Nonsense mutation

Question 13

Which of the following mutations is most likely to severely disrupt the function of a protein?

Accepted Answer

A frameshift mutation early in an exon

Question 14

During translation, which site on the ribosome does the incoming aminoacyl-tRNA first bind?

Accepted Answer

A site

Question 15

Which of the following best describes the function of DNA ligase during DNA replication?

Accepted Answer

Joins Okazaki fragments on the lagging strand

Question 16

A scientist observes a DNA strand with the sequence 5’-ATCG-3’. What is the complementary strand’s sequence and orientation?

Accepted Answer

3’-TAGC-5’

Question 17

Which of the following best explains why a point mutation in an intron is less likely to affect protein function than a point mutation in an exon?

Accepted Answer

Introns are removed during RNA processing.

Question 18

Which enzyme relieves the tension ahead of the replication fork during DNA replication?

Accepted Answer

Topoisomerase

Question 19

If a DNA template strand has the sequence 3’-TACGGT-5’, what is the sequence of the mRNA transcribed from this region?

Accepted Answer

5’-AUGCCA-3’

Question 20

Which of the following statements about Okazaki fragments is correct?

Accepted Answer

They are short DNA fragments synthesized on the lagging strand.

Molecular Biology of the Gene: Structure, Function, and Expression

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