Concepts of Genetics 11th Edition By Klug – Test Bank

Chapter 11   DNA Replication and Recombination

1) Which of the following terms accurately describes the replication of DNA in vivo?

1. A) conservative
2. B) dispersive
3. C) semidiscontinuous
4. D) nonlinear
5. E) nonreciprocal

Answer:  C

Section:  11.1

2) Which term(s) accurately reflect(s) the nature of replication of the chromosome in E. coli?

1. A) bidirectional and fixed point of initiation
2. B) unidirectional and reciprocal
3. C) unidirectional and fixed point of initiation
4. D) multirepliconic and telomeric
5. E) bidirectional and multirepliconic

Answer:  A

Section:  11.2, 11.3, 11.4

3) DNA polymerase III adds nucleotides ________.

1. A) to the 3′ end of the RNA primer
2. B) to the 5′ end of the RNA primer
3. C) in the place of the primer RNA after it is removed
4. D) to both ends of the RNA primer
5. E) to internal sites in the DNA template

Answer:  A

Section:  11.2

4) DNA polymerase I is thought to add nucleotides ________.

1. A) to the 5′ end of the primer
2. B) to the 3′ end of the primer
3. C) in the place of the primer RNA after it is removed
4. D) on single-stranded templates without need for an RNA primer
5. E) in a 5′ to 5′ direction

Answer:  C

Section:  11.2, 11.3

5) Structures located at the ends of eukaryotic chromosomes are called ________.

1. A) centromeres
2. B) telomerases
3. C) recessive mutations
4. D) telomeres
5. E) permissive mutations

Answer:  D

Section:  11.7

6) Which cluster of terms accurately reflects the nature of DNA replication in prokaryotes?

1. A) fixed point of initiation, bidirectional, conservative
2. B) fixed point of initiation, unidirectional, conservative
3. C) random point of initiation, bidirectional, semiconservative
4. D) fixed point of initiation, bidirectional, semiconservative
5. E) random point of initiation, unidirectional, semiconservative

Answer:  D

Section:  11.2, 11.3, 11.4

7) The discontinuous aspect of replication of DNA in vivo is caused by ________.

1. A) polymerase slippage
2. B) trinucleotide repeats
3. C) the 5′ to 3′ polarity restriction
4. D) topoisomerases cutting the DNA in a random fashion
5. E) sister-chromatid exchanges

Answer:  C

Section:  11.3, 11.4, 11.5

8) Assume that a culture of E. coli was grown for approximately 50 generations in 15N (provided in the medium in the ammonium ion), which is a heavy isotope of nitrogen (14N). You extract the DNA from the culture, and it has a density of 1.723 gm/cm3 (water = 1.00 gm/cm3). From the literature, you determine that DNA containing only the common form of nitrogen, 14N, has a density of 1.700 gm/cm3. Bacteria from the 15N culture were washed in buffer and transferred to 14N medium for one generation immediately after which the DNA was extracted and its density determined.

(a) What would be the expected density of the extracted DNA?

(b) After you heat the extracted DNA until it completely denatures (95oC for 15 minutes), what would you expect the density of the DNA in the denatured extract to be? For the purposes of this question, assume that DNA has the same density regardless of whether it is single- or double-stranded.

(c) Assuming that the molar percentage of adenine in the extracted DNA was 20%, what would be the expected molar percentages of the other nitrogenous bases in this DNA?

(d) Assume that a fraction of the extracted DNA was digested to completion with the enzyme snake venom diesterase. This enzyme cleaves between the phosphate and the 3′ carbon. Present a “simplified” diagram that would illustrate the structure of the predominant resulting molecule.

Answer:

(a) approximately 1.712

(b) 1.723 and 1.700

(c) thymine = 20%, guanine = 30%, cytosine = 30%

11) The Meselson and Stahl experiment provided conclusive evidence for the semiconservative replication of DNA in E. coli. What pattern of bands would occur in a CsCl gradient for conservative replication?

Answer:  After one generation in the 14N, there would be two bands, one heavy and one light (no intermediate). After the second generation in the 14N, there would also be two bands, one heavy and one light (no intermediate).

Section:  11.1

12) Given that the nature of DNA replication in eukaryotes is not as well understood as in prokaryotes, (a) present a description of DNA (chromosome) replication as presently viewed in eukaryotes and (b) state the differences known to exist between prokaryotic and eukaryotic DNA replication.

Answer:

(a) Eukaryotic DNA is replicated in a manner very similar to that in E. coli: bidirectional, continuous on one strand and discontinuous on the other, and similar requirements for synthesis (four deoxyribonucleoside triphosphates, divalent cation, template, and primer).

(b) Okazaki fragments are about one-tenth the size of those in bacteria. Different portions of the chromosome (euchromatin, heterochromatin) replicate at different times. There are multiple replication origins in eukaryotic chromosomes.

Section:  11.6

13) Each of the following terms refers to the replication of chromosomes. Describe the role (relationship) of each in (to) chromosome replication.

(a) Okazaki fragment

(b) Lagging strand (c)Bidirectional

Answer:

(a) Okazaki fragment is a short single-stranded stretches of DNA on the lagging strand. See figures in the Klug/Cummings text.

(b) Lagging strand is the side of the replication fork where synthesis is discontinuous. See figures in the Klug/Cummings text.

(c) Bidirectional indicates that from the point of initiation, replication occurs in both directions along the DNA. See figures in the Klug/Cummings text.

Section:  11.3, 11.4