DNA Replication Quiz
Questions: 16 · 10 minutes
1. DNA polymerase inserts an incorrect nucleotide at the growing 3′ end of a new strand. Which activity can immediately remove that mismatch during proofreading?
5′-to-3′ polymerase activity
5′-to-3′ exonuclease activity
3′-to-5′ exonuclease activity
RNA-dependent polymerase activity
2. A dividing eukaryotic cell must maintain the ends of its linear chromosomes despite the end-replication problem. What does telomerase do?
It joins Okazaki fragments throughout the chromosome.
It uses an internal RNA template to extend the 3′ end of chromosome DNA.
It removes mismatched bases from newly synthesized DNA.
It unwinds DNA at every replication origin.
3. During which stage of the eukaryotic cell cycle is nuclear DNA normally replicated?
M phase
G1 phase of interphase
G2 phase of interphase
S phase of interphase
4. Bacteria containing only heavy-isotope DNA are transferred to medium containing a light isotope and allowed one complete round of replication. Under semiconservative replication, what DNA molecules should be present immediately afterward?
Half entirely heavy and half entirely light
All entirely light
All molecules containing heavy and light segments within each strand
All hybrids containing one heavy strand and one light strand
5. At a replication fork, one new strand is made continuously while the other is made in short segments. What best explains this difference?
The two parental strands contain different types of nucleotides.
DNA strands are antiparallel, while DNA polymerase synthesizes only in the 5′-to-3′ direction.
Helicase opens only the template used for continuous synthesis.
DNA ligase prevents continuous synthesis on one side of the fork.
6. A cell can synthesize Okazaki fragments normally, but many unsealed nicks remain in the lagging strand. Which enzyme is most likely impaired?
Primase
Helicase
DNA ligase
Topoisomerase
7. What does it mean to describe DNA replication as semiconservative?
Each daughter molecule contains one parental strand and one newly synthesized strand.
Each daughter strand contains alternating segments of old and newly synthesized DNA.
One daughter molecule contains both parental strands, while the other contains two new strands.
Only selected regions of each parental molecule are copied during a cell cycle.
8. Why are Okazaki fragments produced during DNA replication?
They permit discontinuous 5′-to-3′ synthesis on the lagging-strand template.
They allow both parental strands to be copied continuously toward the replication fork.
They correct bases that helicase inserts incorrectly.
They form when replicated chromosomes exchange matching DNA segments.
9. A drug prevents topoisomerase from functioning ahead of a replication fork. What is the most direct expected result?
RNA primers cannot be produced.
Twisting strain and supercoiling build up ahead of the fork.
Okazaki fragments are joined prematurely.
New DNA is synthesized in the 3′-to-5′ direction.
10. In which direction does DNA polymerase extend a newly forming DNA strand?
From 3′ to 5′ by adding nucleotides to the 5′ end
From 3′ to 5′ by adding nucleotides to the 3′ end
From 5′ to 3′ by adding nucleotides to the 5′ end
From 5′ to 3′ by adding nucleotides to the 3′ end
11. A template strand reads 3′-TACG-5′. Which sequence will be synthesized directly opposite it?
5′-UACG-3′
5′-TACG-3′
5′-ATGC-3′
5′-CGTA-3′
12. Before replication, a template base changes from adenine to guanine and is not repaired. Which base should DNA polymerase place opposite the altered guanine?
Adenine
Thymine
Guanine
Cytosine
13. In bacteria, which enzyme removes RNA primers and replaces them with DNA nucleotides during replication?
DNA ligase
Primase
DNA polymerase I
DNA polymerase III
14. Replication begins at a single origin on a circular bacterial chromosome. What pattern is normally produced as replication proceeds?
Two replication forks move in opposite directions away from the origin.
Many independent fragments copy the chromosome without replication forks.
Both strands are copied continuously in the same direction from the origin.
One fork travels around the chromosome while the other remains at the origin.
15. Why must primase act before a DNA polymerase can begin synthesizing a new DNA segment?
DNA polymerase needs an existing primer with a free 3′-OH group.
DNA polymerase can copy RNA but cannot copy a DNA template.
DNA polymerase must first break the hydrogen bonds between template bases.
DNA polymerase requires ligase to supply its first nucleotide.
16. Which enzyme separates the two parental DNA strands at a replication fork?
DNA ligase
Helicase
Primase
Telomerase