Q: Which equation correctly represents the relationship between the number of base pairs per turn and the pitch of the DNA double helix?

$$\text{Pitch} = \text{Number of base pairs per turn} \times \text{Distance between base pairs}$$

Question 1

Which experiment provided definitive evidence that DNA, and not protein, is the hereditary material in bacteriophages?

Accepted Answer

Hershey–Chase's radioactive labeling experiment

Question 2

A DNA sample contains 28% thymine. According to Chargaff's rules, what percentage of cytosine is present?

Accepted Answer

22%

Question 3

Which structural feature of DNA allows proteins to interact directly with specific base pairs?

Accepted Answer

Major and minor grooves

Question 4

In the Meselson–Stahl experiment, after one round of replication in $$^{14}N $$medium, what banding pattern would be observed if DNA replication were conservative?

Accepted Answer

One band at heavy density and one at light density

Question 5

Which enzyme is responsible for unwinding the DNA helix at the replication fork in E. coli?

Accepted Answer

DnaB

Question 6

Why does the lagging strand of DNA require multiple RNA primers during replication?

Accepted Answer

It is synthesized discontinuously in short fragments opposite to fork movement

Question 7

Which activity of DNA polymerase I is responsible for removing RNA primers from Okazaki fragments?

Accepted Answer

5′ → 3′ exonuclease activity

Question 8

A mutation in the gene encoding telomerase would most likely affect which cellular process?

Accepted Answer

Replication of chromosome ends in germ-line cells

Question 9

Which DNA form is most commonly found under physiological conditions and is described by the classic Watson–Crick double helix?

Accepted Answer

B-DNA

Question 10

During PCR, why must the DNA polymerase be heat-stable?

Accepted Answer

It must survive the high temperature denaturation step at $$95\ ^\circ \mathrm{C}$$

Question 11

Which of the following best explains why a ddNTP terminates DNA synthesis in Sanger sequencing?

Accepted Answer

It lacks a 3′-OH group required for phosphodiester bond formation

Question 12

A patient with Hutchinson-Gilford Progeria Syndrome (HGPS) is found to have shortened telomeres. Which gene is mutated in this disorder?

Accepted Answer

LMNA

Question 13

Which equation correctly represents the relationship between the number of base pairs per turn and the pitch of the DNA double helix?

Accepted Answer

$$	ext{Pitch} = 	ext{Number of base pairs per turn} 	imes 	ext{Distance between base pairs}$$

Question 14

Which protein binds to the 9-mer sequence at oriC and initiates DNA replication in E. coli?

Accepted Answer

DnaA

Question 15

If a DNA polymerase incorporates an incorrect nucleotide, which activity corrects the error, and in which direction does it operate?

Accepted Answer

3′ → 5′ exonuclease activity

Question 16

Which of the following is NOT a function of telomeres?

Accepted Answer

Initiate DNA replication at oriC

Question 17

Which DNA form is left-handed and occurs in regions with repeating CG bases under high salt or low humidity?

Accepted Answer

Z-DNA

Question 18

During DNA replication, which enzyme seals the gap (nick) between Okazaki fragments after primer removal and DNA synthesis?

Accepted Answer

DNA ligase

Question 19

Which step in PCR occurs at $$45	ext{–}68\ ^\circ \mathrm{C}$$ and involves primers binding to complementary target sequences?

Accepted Answer

Primer annealing

Question 20

A researcher wants to amplify a DNA segment longer than 15 kb using PCR. Which limitation must they consider?

Accepted Answer

PCR products longer than 10–15 kb are difficult to make

DNA Structure and Replication: Study Guide for Genetics Exam #3

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