Genetics Chap 3 Quiz

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1

At the conclusion of DNA replication, the two resulting DNA double helices each contain

A) one parental and one progeny strand.

B) two parental or two progeny strands.

C) stretches of progeny DNA interspersed with parental DNA along both strands.

D) two newly synthesized strands.

Answer: A

2

DNA polymerase catalyzes the formation of a phosphodiester bond between a

A) 5′ phosphate and a 5′ hydroxyl group.

B) 3′ phosphate and a 5′ hydroxyl group.

C) 5′ phosphate and a 3′ hydroxyl group.

D) 3′ phosphate and a 3′ hydroxyl group.

Answer: C

3

DNA polymerases are enzymes that copy

A) DNA into DNA.

B) DNA into RNA.

C) RNA into DNA.

D) RNA into RNA.

Answer: A

4

During synthesis, all DNA polymerases add nucleotides in which direction?

A) from left to right

B) from 3′ to 5′

C) from 5′ to 3′

D) in both the 5' to 3' and the 3' to 5' directions

Answer: C

5

In bacteria such as E. coli , replication of the chromosome is

A) semidiscontinuous and bidirectional.

B) discontinuous and unidirectional.

C) continuous and bidirectional.

D) semidiscontinuous and unidirectional.

Answer: A

6

In eukaryotes, DNA replication occurs during which phase of the cell cycle?

A) S

B) G 1

C) G 2

D) M

Answer: A

7

Many types of mammalian cancer cells are notable for their

A) telomerase activity.

B) lack of telomerase activity.

C) lack of telomeres.

D) increased number of telomeres.

Answer: A

8

On the E. coli chromosome, oriC

A) encodes DNA polymerase I.

B) is a binding site for histone proteins.

C) is the start site for replication.

D) encodes an RNA primer.

Answer: C

9

Why, exactly, is a primer necessary to initiate DNA synthesis?

A) The new DNA strand will be composed of linked primers.

B) The primer binds DNA polymerase to the site of new synthesis.

C) The primers are converted into Okazaki fragments, which are then joined to form the new strand.

D) A free 3′-OH group is necessary for DNA polymerase.

Answer: D

10

The 3′ to 5′ exonuclease activity associated with DNA polymerase reduces the frequency of replication errors to

A) 1/10.

B) 1/1,000.

C) 1/1,000,000.

D) 1/1,000,000,000.

Answer: D

11

The enzyme that unwinds the double helix to facilitate replication is

A) 3′ to 5′ exonuclease.

B) DNA helicase.

C) DNA polymerase.

D) topoisomerase.

Answer: B

12

The proofreading activity of DNA polymerase removes errant nucleotides from the ___ of a strand of DNA.

A) 3′ end

B) 5′ end

C) 3′ and 5′ end

D) middle

Answer: A

13

The sequence of nucleotides in one strand of DNA is 5′ - C C A C T G G - 3′ What is the sequence of the complementary strand of DNA?

A) 5′- C C A C T G G - 3′

B) 3′ - C C A C T G G - 3′

C) 5′ - G G T C A C C - 3′

D) 3′ - G G T G A C C - 5′

Answer: D

14

Under a hypothesis of semiconservative DNA replication, Meselson and Stahl expected to see _____ DNA band(s) in the cesium chloride gradient after one round of replication, and _____ band(s) after two rounds of replication.

A) 2; 2

B) 1; 2

C) 1; 1

D) 2; 4

Answer: B

15

Identify the order in which the following enzymes play a role in DNA replication:

A) DNA polymerase, helicase, ligase, primase

B) helicase, primase, DNA polymerase, ligase

C) ligase, primase, DNA polymerase, helicase

D) DNA polymerase, primase, helicase, ligase

Answer: B

16

When the DNA double helix is replicated, the newly synthesized 5′ to 3′ continuous strand is considered the ___ strand.

A) leading

B) lagging

C) template

D) discontinuous

Answer: A

17

Which E. coli DNA polymerase has the ability to "proofread" newly synthesized DNA and remove erroneous bases?

A) DNA polymerase I only

B) DNA polymerase III only

C) DNA polymerase I and III

D) All three DNA polymerases have proofreading ability.

Answer: D

18

What is the difference between a primer and a template?

A) A template is always DNA, whereas a primer can be DNA or RNA.

B) A template is always copied by DNA polymerase, whereas a primer never is.

C) A primer but not a template must have a free 3' hydroxyl group.

D) All of the above are correct.

Answer: D

19

Which of the following is NOT required for DNA synthesis reactions?

A) dCTPs

B) template DNA

C) DNA polymerase

D) calcium ions

Answer: D

20

Which type of DNA is duplicated by rolling circle replication?

A) bacteriophage λ

B) plasmid DNA

C) bacteriophage (ΦX174)

D) all of the above

Answer: D

21

Place the following steps in correct order leading to the formation of a replication bubble at a replicator sequence in the E. coli chromosome.

A. DNA helicases bind to the 13-bp repeat region and untwist the DNA double helix.
B. DNA primase binds to single-strand regions of the replicator sequence, and RNA primers are made.
C. Initiator proteins encoded by the dnaA gene bind to the 9-bp repeats.
D. On the leading strand, DNA polymerase III binds and begins continuously replicating DNA toward the replication fork.

A) A > B > C > D

B) B > C > A > D

C) C > A > B > D

D) D > A > B > C

Answer: C

22

Choose the correct sequence of events occurring on the lagging strand at a replication fork in a bacterial replication bubble:

A. DNA polymerase I, using 3' to 5'nuclease activity, removes the RNA primer and fills the gap with complementary DNA nucleotides.
B. DNA ligase joins the completed DNA Okazaki fragments together, forming a completed new strand of DNA.
C. Primase moves on the lagging strand toward the replication fork and makes a new RNA primer.
D. DNA polymerase III binds at the primer and replicates the lagging strand back to a previously made RNA primer.

A) A > B > C > D

B) B > C > D > A

C) C > D > A > B

D) D > A > B > C

Answer: C

23

Based on the rates of DNA replication at each replication fork in the single replication bubble formed, it takes approximately 42 minutes to replicate the E. coli genome. Yet on enriched media, E. coli cells can demonstrate doubling times of only 20 minutes. How is it possible to make two new cells from one in 20 minutes if it takes 42 minutes to replicate the entire genome?

A) E. coli cells add additional origins of replication as doubling times increase so that they use a more eukaryotic-like replication mechanism as doubling times shorten.

B) E. coli cells increase the number of DNA polymerase III molecules per cell as doubling times shorten so that DNA replication increases.

C) Since E. coli cells have five distinct DNA polymerases at high growth rates, all five forms participate in primary DNA replication.

D) A new round of DNA replication is initiated each cell doubling. This means that when cells are doubling faster than the time it takes to replicate the genome, these cells contain chromosomes that are already beginning a second round of replication before the doubling occurs.

Answer: D

24

Suppose a new organism were just discovered that contains a very unusual DNA polymerase never before seen in any living thing. This DNA polymerase does not require an RNA primer, and it synthesizes DNA from 3' to 5' rather than the usual 5' to 3'. Which enzymes required for replicating the chromosome of E. coli would not be required in this new organism if the organism also had all the conventional bacterial DNA polymerases, unless otherwise stated in the answer?

A) primase, DNA ligase, and DNA polymerase III

B) primase, DNA ligase, and DNA polymerase I

C) primase, DNA helicase, and both DNA polymerases

D) DNA polymerase I

Answer: B

25

In eukaryotes, during S-phase of the cell cycle, the DNA of all chromosomes is replicated using mechanisms relatively similar to those of bacteria. What in addition to the new DNA strands must be made during S-phase to permit the synthesis of the new sister chromatids?

A) two new strands of DNA for each chromosome

B) histone 2A and 2B

C) histone 2A, 2B, 3, and 4

D) two new strands of DNA for each chromosome, and enough histone 2A, 2B, 3, and 4 to double the number of nucleosomes that existed before replication

Answer: D


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