This set of Cytogenetics Interview Questions and Answers focuses on “DNA Replication Eukaryotes – 2”.
1. Cyclin-CDK complex (here considering S cyclin) when active is responsible for phosphorylating several proteins and this often marks then for destruction by ubiquitination. What would be its effect on Cdt activity?
a) Activation
b) Inactivation
c) Destruction
d) Increased synthesis
View Answer
Explanation: Cdt a protein necessary for initiation of replication is sequestered by geminin. S-cyclin-CDK phosphorylates and marks geminin for ubiquitination which makes Cdt free to express its activity. However, it has no effect on Cdt concentration or synthesis.
2. Which of these would you use as a competitive inhibitor for Cdt?
a) MCM 1
b) MCM 2
c) MCM 7
d) MCM 10
View Answer
Explanation: MCM 10 replaces Cdt from pre-replication complex triggering the phosphorylation in the next step. Thus, it must have a similar structure to Cdt and can act as a competitive inhibitor. While there is no MCM 1, MCM 2-7 form a member helicase.
3. What is the fate of phosphorylated Cdc 6?
a) It is transported outside nucleus
b) It is ubiquitinylated
c) It gets activated
d) It forms a complex with Cdt
View Answer
Explanation: Cdc 6 after triggering initiation dissociates from ORC and is phosphorylated to prevent re-initiation. It undergoes ubiquitination and destruction while MCM is phosphorylated and transported outside the nucleus. It ensures that Cdc 6 and MCM remain inactive and can’t re-initiate replication.
4. Pre-replication complex is necessary to initiate replication. It assembles in______________
a) Late Anaphase
b) G1 phase
c) S phase
d) Early Anaphase
View Answer
Explanation: Pre-replication complex assembles on ORC in G1 phase. It is triggered in S phase when no new Pre-RC assembly takes place. Even during early Anaphase and late Anaphase this complex assembly is prevented.
5. Which Cyclin-CDK complex will you find most active in M phase?
a) Cyclin A- CDK 2
b) Cyclin B- CDK 1
c) Cyclin D- CDK 2
d) Cyclin E- CDK 1
View Answer
Explanation: Cyclin B – CDK 1 is corresponding to the yeast M-Cyclin-CDK complex which is active during M phase and leads to Anaphase. Cyclin D is G1-S cyclin, Cyclin A is S cyclin and Cyclin E is G1 cyclin respectively.
6. What is the DNA composition of ARS?
a) A-T rich
b) G-C rich
c) Repeating A-T, G-C sequence
d) No specific sequence speciality
View Answer
Explanation: A-T bases bound by 2 hydrogen bonds unlike G and C, which are bound by 3 hydrogen bonds. In such region DNA strand separation is easier as compared to G-C rich regions. Hence, ARS which requires DNA melting to initiate replication is A-T rich.
7. In an experiment, you are working on mitochondrial chromosomes. Which polymerase will ensure accurate replication?
a) pol beta
b) pol delta
c) pol iota
d) pol gamma
View Answer
Explanation: Pol gamma is the mitochondrial DNA polymerase, while pol beta is mainly necessary for repair. Pol iota associates with translesion DNA synthesis. Pol delta is the primary nuclear DNA polymerase.
8. To your cultured cell lines, you add growth factors like cytokines which act through MAPK cascade pathway. Which transition will it trigger?
a) S->G2
b) M->Anaphase
c) G1->S
d) G2->M
View Answer
Explanation: One of the primary checkpoints to overcome incase of proliferation is G1 -> S check point. MAPK cascade leads to transcription of genes required to increase the CDK activity that leads to this transition. Once S phase is completed the cell must undergo mitosis although there is another checkpoint before Anaphase.
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