Molecular Biology Multiple Choice Questions on “Chromosome Replication Initiates at OriC & Terminates at TerC”.
1. The origin of replication is rich in __________
A. A, T
B. G, C
C. A, G
D. C, T
Answer: A
Explanation: The origin of replication is an A, T rich segment of DNA which unwinds readily but not spontaneously. Unwinding of DNA at this region is controlled by the replication initiation proteins.
2. How many origin of replication are present in the E. coli genome ___________
A. 1
B. 100
C. Uncountable
D. None
Answer: A
Explanation: The E. coli genome has only one origin of replication, thus only one replicon. The eukaryotic genome has multiple origin of replication sites, thus have a multiple replicon system. The origin of replication in E. coli genome is known as the ori C.
3. There are two repeated motifs critical for ori C function. They are ___________
A. 9 mer and 18 mer
B. 6 mer and 9 mer
C. 9 mer and 13 mer
D. 13 mer and 18 mer
Answer: C
Explanation: The two repeated motifs critical for ori C functions are 9 mer and 13 mer. 9 mer is present in 5 copies and 13 mer is present in 3 copies in the origin of replication site.
4. With respect to the ori C motif choose the correctly paired option.
A. 9 mer = 9 times
B. 9 mer = 3 times
C. 13 mer = 5 times
D. 13 mer = 3 times
Answer: D
Explanation: 9 mer is present in 5 copies and 13 mer is present in 3 copies in the origin of replication site. 9 mer is the site of binding of Dna A and 13 mer is the unwinding site of DNA to facilitate replication.
5. Which of the following is not paired with its correct function?
A. 9 mer = binding site for Dna A
B. 13 mer = binding site for replication initiator protein
C. AT rich DNA = unwinding site
D. Dna A = replication initiator protein
Answer: B
Explanation: The replication initiator protein is known as Dna A which binds in the 9 mer region. 13 mer regions is the initial site for the formation of single stranded DNA formation during initiation.
6. Which of the following is not a function of Dna A?
A. DNA binding
B. DNA strand separation
C. Initiates DNA melting
D. Replication protein recruitment
Answer: C
Explanation: Dna A does not initiate DNA melting, that is, DNA strand separation. DNA strand separation takes place at the AT-rich region which unwinds readily. To this readily unwound DNA region at the 13 mer site, the Dna A protein recruits different proteins required for replication initiation.
7. The replication terminus is a segment of a number of ____________ bp.
A. 350
B. 350000
C. 530
D. 530000
Answer: B
Explanation: The replication terminus is a segment of 350 kb region. 350 kb is equivalent to 350000 base pairs and has 6 nearly identical non palindromic sites.
8. The replication terminus involves ____________ identical non palindromic termination site.
A. 2
B. 4
C. 6
D. 8
Answer: C
Explanation: The replication terminus involves 6 identical non palindromic termination sites. They are Ter E, Ter D and Ter A on one side and Ter F, Ter B and Ter C on the other.
9. The termination sites are one way valves known as non-polar valves.
A. True
B. False
Answer: B
Explanation: A replication fork travelling counterclockwise passed through Ter F, Ter B and Ter C but stops upon encountering Ter E, Ter D or Ter A. Similarly a clockwise travelling replication fork transits Ter E, Ter D and Ter A but halts at Ter F, Ter B or Ter C. Thus, these termination sites are polar as they acts as one way valves that allow replication fork to enter the terminus region but not to leave it.
10. The arrest of replication fork motion at Ter sites require the action of ____________ protein.
A. Tus
B. Ter
C. Helicase
D. Topoisomerase
Answer: A
Explanation: The arrest of replication fork is motioned at Ter sites require the action of Tus protein. It is a 309 – residue monomer that is the product of the tus gene.
11. The topological unlinking of DNA in prokaryotes is promoted by ______________
A. Helicase
B. Topoisomerase
C. Tus
D. Dna C
Answer: B
Explanation: The final step in prokaryotic DNA replication is the topological unlinking of the parental DNA strands. This process is catalyzed by topoisomerase.
12. Helicase attaches to the leading strand during replication.
A. True
B. False
Answer: B
Explanation: Helicase is used to unwind the DNA during replication. It attaches to the lagging strand to unwind the DNA helix.
13. The primer used for lagging strand synthesis in prokaryotes is an RNA primer.
A. True
B. False
Answer: B
Explanation: The primer used for leading strand synthesis in prokaryotes is an RNA primer. The primer used for lagging strand synthesis in prokaryotes is a DNA primer.
14. Which enzyme is used to remove the primer from the Okazaki fragment?
A. Endonuclease
B. RNase H
C. 5’ exonuclease
D. Polymerase
Answer: D