Question 1

Which of the following best describes the outcome of Frederick Griffith's experiment when he injected mice with a mixture of heat-killed S strain and live R strain Streptococcus pneumoniae?

Accepted Answer

The mice died, demonstrating that a 'transforming principle' from the dead S strain converted the R strain into a virulent form.

Question 2

In the Hershey-Chase experiment, which isotope labeled the DNA of the bacteriophage, and why was this significant?

Accepted Answer

$$^{32}\mathrm{P}$$ labeled the DNA, demonstrating that DNA, not protein, was the genetic material.

Question 3

Chargaff’s Rules state that in any DNA sample:

Accepted Answer

The amount of purines equals the amount of pyrimidines, and the amount of adenine equals the amount of thymine.

Question 4

Which statement best describes the antiparallel nature of DNA strands in the double helix?

Accepted Answer

One strand runs 5' to 3' and the other runs 3' to 5', allowing complementary base pairing.

Question 5

During DNA replication, which enzyme relieves the tension ahead of the replication fork caused by unwinding of the DNA helix?

Accepted Answer

Topoisomerase

Question 6

Which of the following accurately describes the difference between the leading and lagging strands during DNA replication?

Accepted Answer

The leading strand is synthesized continuously toward the replication fork, while the lagging strand is synthesized discontinuously away from the fork in Okazaki fragments.

Question 7

Which enzyme is responsible for removing RNA primers and replacing them with DNA nucleotides during DNA replication in prokaryotes?

Accepted Answer

DNA polymerase I

Question 8

A patient with xeroderma pigmentosum is highly sensitive to sunlight and prone to skin cancers. This disease is caused by a defect in which DNA repair mechanism?

Accepted Answer

Nucleotide excision repair

Question 9

Telomeres serve an important function in eukaryotic chromosomes. What happens to telomeres with each round of DNA replication, and which enzyme counteracts this effect in certain cell types?

Accepted Answer

Telomeres shorten with each replication; telomerase extends them in germ cells and some stem cells.

Question 10

Which of the following best describes the structure and function of a nucleosome?

Accepted Answer

A nucleosome is a segment of DNA wrapped around a core of eight histone proteins, helping to compact DNA within the nucleus.

Question 11

Which of the following is a key structural and functional difference between euchromatin and heterochromatin?

Accepted Answer

Euchromatin is less condensed and transcriptionally active, while heterochromatin is more condensed and transcriptionally inactive.

Question 12

Which of the following best explains why DNA polymerase requires a primer to begin synthesis?

Accepted Answer

DNA polymerase can only add nucleotides to an existing 3' hydroxyl group provided by the primer.

Question 13

Which of the following accurately describes the role of single-stranded binding proteins during DNA replication?

Accepted Answer

They prevent the separated DNA strands from re-annealing during replication.

Question 14

Which of the following is NOT a component of the reaction catalyzed by DNA polymerase during DNA synthesis?

Accepted Answer

A ribonucleoside triphosphate (rNTP) as the main substrate

Question 15

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

Accepted Answer

Each daughter DNA molecule consists of one parental strand and one newly synthesized strand.

Question 16

Which of the following best describes the difference in origin of replication between prokaryotic and eukaryotic cells?

Accepted Answer

Prokaryotic chromosomes have a single origin of replication, while eukaryotic chromosomes have multiple origins.

Question 17

Which of the following is a mechanism used by DNA polymerases to ensure high fidelity during DNA replication?

Accepted Answer

Proofreading activity that removes incorrectly paired nucleotides using 3' to 5' exonuclease activity.

Question 18

Which two macromolecules make up eukaryotic chromosomes?

Accepted Answer

DNA and protein

Question 19

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

Accepted Answer

It joins Okazaki fragments on the lagging strand by forming phosphodiester bonds.

Question 20

Which of the following best describes the process and significance of nucleotide excision repair?

Accepted Answer

It removes thymine dimers caused by UV light by excising a segment of the damaged strand and filling in the gap with DNA polymerase and ligase.

The Molecular Basis of Inheritance and DNA Replication

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