Molecular Biology Principles And Practice 2nd Edition by Micheal Cox – Test Bank

Chapter 11

1. Which of the following is not a correct description of DNA replication in bacteria?

A. DNA replication is semiconservative.
B. DNA replication is discontinuous.
C. DNA replication is dispersive.
D. DNA replication begins at origins of replication and proceeds bidirectionally.
E. DNA replication is semiconservative and dispersive.

Answer: C
Section: 11.1
Level: Easy
Blooms: Remembering

2. Watson and Crick proposed that during DNA replication the double helix is unwound and each parental DNA strand is used as a template to generate a new daughter strand. What is this mode of replication called?

A. conservative replication
B. semiconservative replication
C. dispersive replication
D. discontinuous replication
E. continuous replication

Answer: B
Section: 11.1
Level: Easy
Blooms: Remembering

3. Multiple models were proposed to explain replication. What experimental approach allowed researchers to distinguish between them?

A. Cells were pulsed with high specific activity [3H] thymidine to show the direction of DNA synthesis on the chromosome.
B. Cells infected with T4 bacteriophage were grown in the presence of radioactive nucleotides. When DNA was analyzed in alkaline CsCl gradients, the presence of short DNA fragments indicated that discontinuous replication had occurred.
C. Bacteria were grown on 15NH4 until the entire DNA contained heavy nitrogen and then the cells were transferred to normal, light media for one round of replication. The resulting DNA molecules were separated in density gradients and compared to the expected results for each proposed model.
D. Bacteria were grown on [3H] thymidine until the entire DNA contained heavy thymidine and then the cells were transferred to normal, light media for one round of replication. The resulting DNA molecules were separated in density gradients and compared to the expected results for each proposed model.
E. None of these choices is correct.

Answer: C
Section: 11.1
Level: Medium
Blooms: Understanding

4. How did Meselson and Stahl distinguish between semiconservative and conservative replication in their experiment?

A. After two rounds of replication, only mixed DNA molecules were present in the gradient.
B. After one round of replication, only mixed DNA molecules were present in the gradient.
C. After one round of replication, only heavy DNA molecules were present in the gradient.
D. After one round of replication, only mixed DNA strands were present in alkaline gradients.
E. After two rounds of replication, only heavy DNA strands were present in alkaline gradients.

Answer: B
Section: 11.1
Level: Medium
Blooms: Understanding

5. How did Meselson and Stahl distinguish between semiconservative and dispersive replication in their experiment?

A. After one round of replication, only mixed DNA molecules were present in native gradients.
B. After two rounds of replication, only mixed DNA molecules were present in the gradient.
C. After two rounds of replication, both heavy and light DNA molecules were present in the gradient.
D. After one round of replication, both heavy and light DNA single-strands were present in alkaline gradients.
E. After two rounds of replication, only heavy DNA strands were present in alkaline gradients.

Answer: D
Section: 11.1
Level: Hard
Blooms: Understanding

6. Observing replication of circular plasmid DNAs by electron microscopy showed that:

A. replication initiates at multiple origins, creating multiple replication bubbles in the plasmid.
B. template strands completely unwind before replication starts.
C. replication initiates from a single origin, creating a single replication bubble in the plasmid.
D. the plasmid DNA must become linear before replication can initiate at each end of the linear plasmid.
E. replication occurred only at one replication fork of the bubble created.

Answer: C
Section: 11.1
Level: Medium
Blooms: Understanding

7. Bidirectional synthesis was demonstrated by which of the following methods?

A. Bacteria were grown on 15NH4 until the entire DNA contained heavy nitrogen and then the cells were transferred to normal, light media for one round of replication. The resulting DNA molecules were separated in density gradients and compared to the expected results for each proposed model.
B. Cells were labeled with low specific activity [3H] thymidine followed by a pulse of high specific activity [3H] thymidine. This experiment revealed that a new strand was growing away from the midpoint toward one fork.
C. Cells infected with T4 bacteriophage were grown in the presence of radioactive nucleotides. When DNA was analyzed in alkaline CsCl gradients, the presence of short DNA fragments indicated that bidirectional synthesis had occurred.
D. Cells were labeled with low specific activity [3H] thymidine followed by a pulse of high specific activity [3H] thymidine. This experiment revealed a gradient of radioactive density that is heaviest at both forked junctions.
E. None of these answers is correct.

Answer: D
Section: 11.1
Level: Hard
Blooms: Understanding

8. Each replication fork requires both leading and lagging strand synthesis because

A. DNA synthesis must be complementary.
B. DNA polymerases can only synthesize DNA 3′ to 5′.
C. the DNA templates are antiparallel and yet the DNA polymerases only work in one direction.
D. the helicase unwinds one strand faster than the other.
E. All of these choices are correct.

Answer: C
Section: 11.1
Level: Easy
Blooms: Analyzing

9. How did Okazaki show that DNA synthesis is semidiscontinuous?

Answer: Okazaki proposed that DNA synthesis was discontinuous on the lagging strand, needing to reinitiate as the DNA duplex unwound. This repeated initiation would generate short fragments that would have to be connected. The evidence for this mechanism came from growing T4-infected bacteria on radioactive nucleotides for brief time intervals and then analyzing the resulting DNA on CsCl gradients. Small fragments were observed as predicted.

Section: 11.1
Level: Hard
Blooms: Understanding

10. Which of the following is not necessary for a DNA polymerase reaction?

A. template DNA
B. primer strand
C. ATP
D. dNTPs
E. All of these components are necessary.

Answer: C
Section: 11.2
Level: Easy
Blooms: Understanding