Question 1

Which experimental finding most directly led to the conclusion that DNA, and not protein, is the genetic material in cells?

Accepted Answer

Experiments showing that only DNA from viruses enters bacterial cells during infection.

Question 2

According to Chargaff’s rules, if a DNA sample from a newly discovered organism contains 32% adenine, what percentage of guanine would you expect to find?

Accepted Answer

$$18\%$$

Question 3

Which of the following best explains why pairing a purine with a pyrimidine in the DNA double helix results in a uniform width?

Accepted Answer

Purines are larger than pyrimidines, so pairing two purines would make the helix too wide.

Question 4

A scientist mutates the gene encoding DNA ligase in a eukaryotic cell. Which process would be most directly affected?

Accepted Answer

Joining of Okazaki fragments on the lagging strand.

Question 5

During DNA replication, which enzyme is responsible for relieving the strain caused by unwinding of the double helix?

Accepted Answer

Topoisomerase

Question 6

Which of the following statements about DNA polymerase is correct?

Accepted Answer

It adds nucleotides only to the free $$3'$$ end of a growing DNA strand.

Question 7

A patient is exposed to X-rays, which cause damage to their DNA. Which repair mechanism is most likely to remove and replace the damaged DNA segment?

Accepted Answer

Nucleotide excision repair

Question 8

Why do eukaryotic chromosomes have multiple origins of replication, whereas most prokaryotic chromosomes have only one?

Accepted Answer

Eukaryotic chromosomes are much larger and linear, so multiple origins speed up replication.

Question 9

Which of the following best describes the semiconservative model of DNA replication?

Accepted Answer

Each daughter DNA molecule consists of one parental strand and one new strand.

Question 10

A mutation causes a eukaryotic cell to lack telomerase activity. What is the most likely consequence after many cell divisions?

Accepted Answer

The cell’s chromosomes will gradually shorten, potentially losing essential genes.

Question 11

Which of the following is a function of histone proteins in eukaryotic cells?

Accepted Answer

They are responsible for the main level of DNA packing in chromatin.

Question 12

Which chromatin structure is most likely to be transcriptionally active?

Accepted Answer

Euchromatin

Question 13

A researcher observes that a certain region of DNA is highly condensed and not expressed in a cell. This region is most likely:

Accepted Answer

Heterochromatin

Question 14

Which of the following best explains why mutations are important in evolution?

Accepted Answer

They are the source of genetic variation upon which natural selection acts.

Question 15

Which of the following statements about Okazaki fragments is correct?

Accepted Answer

They are joined together by DNA ligase to form the lagging strand.

Question 16

A cell is observed to have a high rate of telomerase activity. Which of the following is a likely characteristic of this cell?

Accepted Answer

It is a germ cell or a cancer cell.

Question 17

Which of the following best describes the role of primase during DNA replication?

Accepted Answer

It synthesizes short RNA primers needed for DNA polymerase to begin synthesis.

Question 18

If a mutation prevents the formation of single-strand binding proteins during DNA replication, what is the most likely immediate effect?

Accepted Answer

Single-stranded DNA will re-anneal or form secondary structures, hindering replication.

Question 19

Which of the following is true regarding the difference between ATP and dATP?

Accepted Answer

dATP contains deoxyribose, while ATP contains ribose.

Question 20

A mutation in a histone tail alters its chemical modification. Which of the following is a possible consequence?

Accepted Answer

Chromatin condensation may change, affecting gene expression.

The Molecular Basis of Inheritance: DNA Structure, Replication, and Chromosome Organization

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