This set of Cytogenetics Multiple Choice Questions & Answers (MCQs) focuses on “DNA Replication Eukaryotes – 1”.
1. In case of eukaryotes replication initiates at ________
b) CpG islets
Explanation: Replication begins at ARS – Autonomous Replicating Sequences. While TATA and CpG islets are characteristics of promoter elements which controls transcription. Translation initiates at AUG codon.
2. Here are names of some factors necessary for prokaryotic replication. Which of these or their homologue is unnecessary for eukaryotes?
a) Dna G
b) Dna b
c) Beta clamp
Explanation: DNA G (gyrase) is not needed for eukaryotes. While Dna b homologue MCM, Beta clamp homologue PCNA and SSB homologue RPA are necessary.
3. You wanted to find out the importance of the DNA polymerases. So, you mutated the polymerases one by one and checked for survival. In which of these mutant cases will you see least survival rate?
Explanation: Alpha has primase activity. Without a primer DNA synthesis can’t initiate thus Alpha polymerase is indispensible. While the beta is mainly needed for repair mechanisms it doesn’t make much difference. However, delta and eta are main polymerases for eukaryotes and their mutation will have major effects as well.
4. You design a circular ssDNA with a labeled RNA primer (alpha-P32 labeling). You add polymerase epsilon and required enzymes for replication to the fragment. What will you expect to see on autoradiography after gel electrophoresis?
a) Single labeled band with some labeling at the bottom region
b) Two labeled band one much lower than the other with labeling at the bottom region
c) No band but labeling at the bottom
d) Two labeled band one much lower than the other with no labeling at the bottom
Explanation: Alpha-P32 incorporated the label in the entire RNA primer fragment. As polymerization will take place the 5’->3’ exonuclease activity of pol eta will produce labeled oligomers of that RNA. One band will correspond to unreplicated DNA, the lower one to oligomer. No labeled monomer is produced.
5. You design a plasmid with a gene for Histidine synthesis and a fragment containing ARS. You introduce it yeast culture and try to grow then in Histidine deficit media. What will be your observation?
a) No growth
b) One or two colonies
c) Rapid growth with many colonies
d) Normal growth with countable colonies
Explanation: ARS promotes replication of the yeast. Even if the plasmid was initially taken up by few cells due to rapid replication brought about by ARS the number of colony massively increases. If the same experiment was done with any random stretch of DNA none or few colonies would be seen.
6. Deletion of which domain of ARS would give the least replication rate in eukaryotes?
a) A domain
b) B1 domain
c) B2 domain
d) B3 domain
Explanation: The 11bp ‘A domain’ is the primary functional area of the ARS. Mutation in this domain gives 0% functionality of ORC so lease replication. Other mutations also reduce replication rate but not to such extent.
7. Which subunit in MCM is not phosphorylated in MCM after initiation is triggered?
Explanation: MCM has 6 subunits numbered from 2 to 7. After initiation of replication is triggered all subunits other than 2 are phosphorylated.
8. You are given a DNA fragment with a CBD lesion. Which polymerase(s) will you use to replicate this fragment without taking care of the error?
a) ζ (zeta), η (eta)
b) η (eta), ) θ (theta)
c) θ (theta), κ (kappa)
d) κ (kappa),θ (theta)
Explanation: Eta introduces two random base against the lesion say AA or TT. However, it is very error prone and requires zeta to carry out the remaining replication. Kappa and theta also participate in repair but by other ways.
9. We know that Beta clamp in bacteria has two subunits and takes the shape of a ring. Which of this will be characteristic of PCNA which is a beta clamp homologue for eukaryotes?
a) Two subunits forming ring
b) Three subunits forming ring
c) Four subunits forming figure 8 like structure
d) Four subunits forming a larger ring
Explanation: PCNA has three subunits but its structure is similar (ring) like two subunit beta clamp. Larger ring formation would be unreasonable as the basic structure of DNA is exactly the same for both prokaryotes and eukaryotes.
10. What is the function of RFC in eukaryotic replication?
a) Catalytic subunit
c) Clamp loader
Explanation: RFC or Replication Factor C is the eukaryotic homologue of clamp loader. It loads the PCNA clamp. Eukaryotic replication primer is formed by alpha polymerase while RPA acts as SSB.
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