Molecular Biology Multiple Choice Questions on “Recombination in Higher Organisms – 1”.
1. RecA protein of E. coli is involved in the process of ____________
A. Pairing of homologous DNA
B. Introduction of DSB
C. Assembly of strand exchange
D. Resolution of Holiday junction
Answer: A
Explanation: In E. coli, RecA protein is involved in pairing homologous DNA and strand invasion. In eukaryotes, Rad 51 is involved in this same process.
2. RecBCD and RecFOR in E. coli is involved in the process ____________
A. Assembly of strand exchange
B. Holiday junction recognition
C. Introduction of DSB
D. Resolution process
Answer: A
Explanation: RecBCD and RecFOR in E. coli are involved in the assembly of strand exchange proteins. In eukaryotes Rad52 and Rad59 are involved in this same process.
3. In bacteria specific proteins are involved in the RecBCD pathway.
A. True
B. False
Answer: B
Explanation: In bacteria, no specific proteins have been found that performs the RecBCD pathway. Breaks result in the damage of DNA, missteps in DNA repair or collapse of a replication fork.
4. What is the holiday junction resolving enzyme?
A. RecA
B. RuvC
C. Rad52
D. Rad59
Answer: B
Explanation: RuvC in E. coli is the holiday junction resolving enzyme. In eukaryotes this function is performed by the enzyme Rad51C-XRCC3 complex.
5. RecBCD enzyme has polymerase and transcriptase activity.
A. True
B. False
Answer: B
Explanation: RecBCD enzyme has both DNA helicase and nuclease activity. It processes broken DNA molecules of DNA by the process of recombination.
6. RecBCD pathway is an ATP dependent process.
A. True
B. False
Answer: A
Explanation: The RecBCD complex binds to DNA molecules at the site of DSB and tracks along DNA using the energy of ATP hydrolysis as a result the DNA is unwound.
7. Chi is the control site of the RecBCD pathway.
A. True
B. False
Answer: A
Explanation: The activities of RecBCD are controlled by specific DNA sequence elements known as Chi sites. Chi sites were discovered because they stimulate the frequency of homologous recombination.
8. What are the helicase components of the RecBCD pathway?
A. RecB, RecC
B. RecC, RecD
C. RecB, RecD
D. RecA, RecB
Answer: C
Explanation: RecB and RecD subunits are both DNA helicases. These enzymes use ATP hydrolysis to melt and unwind the base pairing of DNA double strand.
9. What is the function of Rec component?
A. 5’→3’ helicase activity
B. 3’→5’ helicase activity
C. Recognize Chi sites
D. Nuclease activity
Answer: C
Explanation: Rec functions recognize Chi sites. Chi sites are the controlled sites of RecBCD pathway.
10. What are the two components of RecBCD pathway involved as motor parts?
A. RecB, RecD
B. RecB, RecC
C. RecB, RecA
D. RecC, RecD
Answer: A
Explanation: RecB and RecD helicase act as motors help to move independently along opposite strands of the DNA duplex and at different speeds. RecB and RecD are helicase parts of the RecBCD pathway.
11. What is the speed of driving the RecBCD along the DNA?
A. More than 2000 bp per second
B. More than 1000 bp per second
C. More than 200 bp per second
D. More than 100 bp per second
Answer: B
Explanation: RecB and RecD are capable together of driving the RecBCD complex along the DNA at rates of greater than 1000 bp per second. Chi sites within DNA act as a sort of molecular throttle to regulate the activities of the helicases and therefore the speed of DNA translocation.
12. How many times the frequency is increased by the Chi sites?
A. ≈10 fold
B. ≈20 fold
C. ≈30 fold
D. ≈40 fold
Answer: A
Explanation: Chi sites increase the frequency of recombination by ≈10 fold. This stimulation is most pronounced directly adjacent to the Chi sites.
13. The nuclease activity of the RecBCD is prone to digest the bacterial cell wall from foreign DNA.
A. True
B. False
Answer: B
Explanation: The ability of Chi sites to control the nuclease activity of RecBCD also helps bacterial cell protect them from foreign DNA. This foreign DNA may enter via phage infection or conjugation.
14. What is the sequence of the Chi site that is highly found in the E. coli genome?
A. GATAATCC
B. GCTGGTGGC
C. CCGGACCTT
D. ATGCCGCC
Answer: B
Explanation: The 8 nucleotide Chi site is GCTGGTGGC. It is found in high concentrations in the E. coli genome.
15. If the foreign DNA lacks the Chi site what will happen?
A. Chi site of DNA will destroy
B. Foreign DNA is not affected
C. Foreign DNA easily enters the cell
D. DNA sequence will be intact as previous
Answer: C