This set of Molecular Biology Multiple Choice Questions & Answers (MCQs) focuses on “DNA Replication Occurs at the Replication Fork”.
1. Semiconservative nature of replication of eukaryotic chromosome was first demonstrated by _______________
a) Walter Flemming on root tip cells of Vicia faba
b) J. Herbert Taylor, Philip Wood and Walter Hughes on root tip cells of Vicia faba
c) Walter Flemming on root tip cells of Phaseolus vulgaris
d) J. Herbert Taylor, Philip Wood and Walter Hughes on root tip cells of Phaseolus vulgaris
View Answer
Explanation: Walter Flemming discovered cell division not semi conservative nature of replication. Semiconservative nature of replication was first demonstrated by J. Herbert Taylor, Philip Wood and Walter Hughes on root tip cells of broad bean which is the common name for Vicia faba.
2. Pick the correct pair with respect to primers used in DNA replication.
a) RNA primer- for prokaryotes only
b) DNA primer-for eukaryotes only
c) DNA primer- for both prokaryotes and eukaryotes
d) RNA primer- for both prokaryotes and eukaryotes
View Answer
Explanation: Short oligonucleotides of RNA are required by DNA polymerase for the synthesis of both leading and lagging strands of DNA due to the requirement of free 3’ end for DNA synthesis. As formation of oligonucleotides of DNA by DNA polymerase also requires a free 3’ end thus, DNA primers are not applicable for the synthesis of new strands of DNA during replication.
3. Which of the following is correctly matched with its subsequent role?
a) Topoisomerase II- can remove both positive and negative supercoil in the DNA duplex
b) Polymerase I- larger fragment responsible for exonuclease activity
c) DnaA protein- responsible for “melting” of the DNA double helix during replication
d) DnaB protein- attaches to the newly unwounded single strand of DNA to prevent folding of the strand
View Answer
Explanation: The reasons are
i) Topoisomerase II- converts a positive supercoil to a negative supercoil, also known as gyrase
ii) Polymerase I- larger (klenow) fragment is responsible for polymerase activity
iii) DnaB protein- also known as helicase helps in unwinding of DNA duplex to form the open complex.
4. Replication fork is the junction between the two ___________
a) Unreplicated DNA
b) Newly synthesized DNA
c) Newly separated DNA strands and newly synthesized DNA strands
d) Newly separated DNA strands and the unreplicated DNA
View Answer
Explanation: As both the strands of DNA occur simultaneously the two template strands undergo separation. The junction between the newly separated DNA strands and the unreplicated DNA is known as the replication fork.
5. Which of the following does not affect DNA replication?
a) Antiparallel nature of DNA
b) End specificity of polymerase
c) SSB protein
d) Helicase
View Answer
Explanation: The antiparallel nature of DNA and end specificity of polymerase of polymerase leads to two types of strand synthesis, leading and lagging strands. Helicase helps in the unwinding of the DNA helix. SSB protein binds to the single stranded DNA during replication to stabilize it but does not take any part in new strand synthesis.
6. Who was the first person to analyse the process of replication and on which organism?
a) Arthur Kornberg: E. coli
b) John Cairns: E. coli
c) Arthur Kornberg: Bacillus subtilis
d) John Cairns: Bacillus subtilis
View Answer
Explanation: The person who first analyzed the process of replication was John Cairns in which E. coli were grown in the presence of radioactive Thymidine. This allowed subsequent visualization of newly replicated DNA by autoradiography.
7. In the case of a circular DNA synthesis how many replication forks are observed?
a) 1
b) 2
c) 3
d) 4
View Answer
Explanation: In case of replication of a complete circular DNA molecule 2 replication forks are observable. This represents the regions of active DNA synthesis and is represented in form of a bubble known as the replication bubble.
8. Primer synthesis short stretches of DNA for replication.
a) True
b) False
View Answer
Explanation: Primer synthesizes short stretches of RNA for replication. These RNA serves as primers for the synthesis of both the leading and lagging strand during replication.
9. Which of the following is not used for degrading RNA from RNA:DNA hybrid in replication?
a) RNase A
b) RNase H
c) Polymerase I
d) Exonuclease
View Answer
Explanation: RNase H dissolves RNA in eukaryotes and the last rNTP connected directly to the dNTP is digested by exonuclease. Polymerase I hydrolyses RNA in the 5’ – 3’ direction in prokaryotes. RNase A is not required in replicative purpose.
10. The gaps formed by the hydrolyzing the RNA from RNA:DNA hybrid is filled by DNA polymerase I and the nicks are ligated by T4 ligase.
a) True
b) False
View Answer
Explanation: The gaps formed by the hydrolyzing the RNA from RNA:DNA hybrid is filled by DNA polymerase δ. The nicks are then filled in by T4 ligase at the cost of an ATP yielding an intact lagging strand.
11. Which of the following is correctly matched with its subsequent role?
a) Topoisomerase II- can remove both positive and negative supercoil in the DNA duplex
b) Polymerase I- larger fragment responsible for exonuclease activity
c) DnaA protein- responsible for “melting” of the DNA double helix during replication
d) DnaB protein- attaches to the newly unwounded single strand of DNA to prevent folding of the strand
View Answer
Explanation: The reasons are
i) Topoisomerase II- converts a positive supercoil to a negative supercoil, also known as gyrase.
ii) Polymerase I- larger (Klenow) fragment is responsible for polymerase activity.
iii) DnaB protein- also known as helicase helps in unwinding of DNA duplex to form the open complex.
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