Question 1

Which experiment first demonstrated that DNA could transform the properties of cells, and what was the key finding?

Accepted Answer

Griffith's experiment; he found that harmless bacteria could become pathogenic by assimilating genetic material from heat-killed pathogenic bacteria.

Question 2

According to Chargaff's rules, if a DNA sample from a species contains 30% adenine, what percentage of guanine would you expect to find?

Accepted Answer

$$20\%$$

Question 3

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

Accepted Answer

A purine-pyrimidine pair matches the width observed in X-ray crystallography, maintaining a consistent diameter of $$2\ \mathrm{nm}.$$

Question 4

What is the role of DNA polymerase during DNA replication?

Accepted Answer

It catalyzes the addition of nucleotides to the 3' end of a growing DNA strand.

Question 5

Which enzyme is responsible for relieving the strain caused by the unwinding of the DNA double helix during replication?

Accepted Answer

Topoisomerase

Question 6

During DNA replication, why is the lagging strand synthesized in short fragments?

Accepted Answer

The lagging strand template runs in the 3' to 5' direction, so DNA polymerase must synthesize away from the replication fork in short segments called Okazaki fragments.

Question 7

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 newly synthesized strand.

Question 8

A mutation occurs during DNA replication. Which repair mechanism is most likely to correct a mismatched base pair that escaped proofreading?

Accepted Answer

Mismatch repair

Question 9

Why are telomeres important for eukaryotic chromosomes?

Accepted Answer

They prevent the loss of genes near the ends of chromosomes during repeated rounds of DNA replication.

Question 10

Which enzyme is responsible for joining Okazaki fragments on the lagging strand during DNA replication?

Accepted Answer

DNA ligase

Question 11

A scientist is sequencing a DNA strand and finds the following sequence on one strand: 5'-ATCGGCTA-3'. What is the complementary sequence on the other strand?

Accepted Answer

3'-TAGCCGAT-5'

Question 12

Which of the following statements about chromatin structure in eukaryotes is correct?

Accepted Answer

Euchromatin is loosely packed and accessible for gene expression.

Question 13

Which of the following best describes the function of single-strand binding proteins during DNA replication?

Accepted Answer

They stabilize unwound DNA strands and prevent them from re-annealing.

Question 14

A patient is exposed to X-rays, which cause thymine dimers in their DNA. Which repair mechanism is most likely to fix this damage?

Accepted Answer

Nucleotide excision repair

Question 15

Which of the following is true regarding the directionality of DNA synthesis?

Accepted Answer

DNA is synthesized in the 5' to 3' direction.

Question 16

Which of the following best explains why prokaryotes do not face the same problem with chromosome shortening as eukaryotes?

Accepted Answer

Prokaryotic chromosomes are circular, so they do not have ends that shorten during replication.

Question 17

Which of the following statements about histones and nucleosomes is correct?

Accepted Answer

A nucleosome consists of DNA wrapped around eight histone proteins.

Question 18

A mutation in the gene encoding DNA ligase would most likely result in which of the following problems during DNA replication?

Accepted Answer

Inability to join Okazaki fragments on the lagging strand.

Question 19

Which of the following best describes the evolutionary significance of mutations that escape DNA repair mechanisms?

Accepted Answer

They are a source of genetic variation, which can be acted upon by natural selection.

Question 20

Which of the following is a correct sequence of events in nucleotide excision repair?

Accepted Answer

Nuclease removes the damaged DNA, DNA polymerase fills the gap, and DNA ligase seals the nick.

DNA Structure, Replication, and Packaging: Study Notes for General Biology

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