Question

Which cyclin is used to initiate anaphase onset, and what is its target to initiate anaphase onset?

Group of answer choices

Cyclin B and its target is cdc20

Cyclin D and its target is securin

Cyclin D and its target is seperase

Cyclin B and its target is securin

Cyclin B and its target is seperase

Answer 1

Answer: Option A. Cyclin B and its target is cdc20.

Explanation: Cyclin B is an important protein kinase as it helps in the regulation of Mitotic phase transition. Its direct targets include Seperase, cdc20, cdc25 and wee1.

- cdc20 is a ubiquitin ligase that helps in progression of cell cycle. Cyclin B activates this cdc20 in order to initiate anaphase onset.

Incorrect options:

- Cyclin D is used to check the cell growth completeness before passing to the Start point. There levels are high in G1 phase. The question is about mitotic phase. This makes Options B and C incorrect.

- Securin is not the direct target of Cyclin B. This makes Option D incorrect.

- Separase is also a direct target of Cycline B. Separase basically initiates the sister chromatid segregation. Cyclin B phosphorylates separase, thus inhibiting its catalytic activity. This knocks out the Option E.