Question 1

Which experiment provided the first direct evidence that DNA, and not protein, is the genetic material in viruses?

Accepted Answer

Alfred Hershey and Martha Chase's experiment using radioactive isotopes with bacteriophage T2

Question 2

In the Hershey-Chase experiment, which radioactive isotope was used to label DNA, and why was this important?

Accepted Answer

Radioactive phosphorus ($$^{32}P$$), because phosphorus is found in DNA but not in protein

Question 3

Chargaff’s rules state that in any species, the amount of adenine (A) equals the amount of thymine (T), and the amount of guanine (G) equals the amount of cytosine (C). If a DNA sample contains 30% adenine, what percentage of guanine does it contain?

Accepted Answer

20%

Question 4

Which feature of DNA structure did Rosalind Franklin’s X-ray diffraction images help Watson and Crick deduce?

Accepted Answer

The helical shape and uniform width of the molecule

Question 5

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

Accepted Answer

Purine-purine pairs are too wide and pyrimidine-pyrimidine pairs are too narrow, but purine-pyrimidine pairs fit the X-ray data

Question 6

During DNA replication, which enzyme is responsible for unwinding the double helix at the replication fork?

Accepted Answer

Helicase

Question 7

What is the function of single-strand binding proteins during DNA replication?

Accepted Answer

They stabilize and protect single-stranded DNA until it can be used as a template

Question 8

Which enzyme corrects 'overwinding' ahead of the replication fork by breaking, swiveling, and rejoining DNA strands?

Accepted Answer

Topoisomerase

Question 9

Why can DNA polymerase only add nucleotides to the 3' end of a growing DNA strand?

Accepted Answer

The enzyme's active site is specific for the 3' hydroxyl group

Question 10

In eukaryotic cells, what is the role of telomeres during DNA replication?

Accepted Answer

They postpone the erosion of genes near the ends of DNA molecules

Question 11

Which enzyme catalyzes the lengthening of telomeres in germ cells?

Accepted Answer

Telomerase

Question 12

What is the main 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

Question 13

Which process describes the joining of Okazaki fragments on the lagging strand?

Accepted Answer

DNA ligase joins the fragments together

Question 14

If a DNA molecule has the following sequence on one strand: 5'-ATCGGCTA-3', what is the complementary sequence on the other strand?

Accepted Answer

3'-TAGCCGAT-5'

Question 15

Which model of DNA replication was supported by the Meselson-Stahl experiment?

Accepted Answer

Semiconservative model

Question 16

A mutation causes DNA polymerase to lose its proofreading ability. What is the most likely consequence?

Accepted Answer

Increased frequency of mutations due to unrepaired errors

Question 17

Which of the following best describes the process of transformation as discovered by Griffith?

Accepted Answer

A change in genotype and phenotype due to assimilation of foreign DNA

Question 18

Which of the following is NOT a direct cause of DNA damage that may require nucleotide excision repair?

Accepted Answer

DNA polymerase proofreading

Question 19

If a eukaryotic chromosome undergoes repeated rounds of replication without telomerase activity, what is the most likely outcome?

Accepted Answer

Essential genes near the ends may be lost, leading to cell dysfunction or death

Question 20

Which of the following statements about DNA replication is correct?

Accepted Answer

Replication proceeds in both directions from each origin until the entire molecule is copied

The Molecular Basis of Inheritance (Chapter 16) – Study Notes

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