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Cell Cycle

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Published in: Biology
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Notes On Cell Cycle.

Anwesha B / Kolkata

5 years of teaching experience

Qualification: M.Sc in Zoology

Teaches: Biology, Zoology

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  1. CELL CYCLE cyclin B/A CDK 1 Cyclin D CDK cyclin E CDK 2 Cyclin A CDK 2 The family of protein kinases that control the cell cycle has 2 subunits — i) Regulatory subunit — Cyclin ii) Catalytic subunit— CDK CDKs are inactive in the absence of cyclin. CDKs are activated by phosphoryation. CDK activity is low in early Gl phase, which promotes pre-replication complex at the origin of replication. By, the end of Gl, CDK 4,6 associates with cyclin D. These cyclins phosphorylates pRb which leads to transcription of a number of genes, including those that code for Cyclin E and A and CDK 1. Late Gl Cyclin E Rb E2F [E2F is inactive when bound to Rb] E2F [E2F is unbound and is active] Transcription of S-phase CDKs
  2. During G2 to M transition Threonine-161 residue of CDKI gets phosphorylated by CAK and simultaneously Weel (kinase) phosphorylates Tyrosine-15 residue. Cdc 25 (phosphatase) dephosphorylates Tyr.-15 residue. This activates the Cdk1-cyclinB complex and the cell enters the mitosis. By the end of mitosis Thr.-161 is dephosphorylated. The cyclin becomes free and is degraded and the cell starts another cycle. Thr. 161 Thr. 161 Tyr. 15 CAK Wee I Cdc 25 Post-mitotic fission Cdk 1 (inactive) Cdk 1 cyclin (inactive) Cdkl cyclin cyclin (active) Cdk 1 cyclin Cdk 1 cyclin (degraded) Cyclin destruction occurs when a cell moves from one phase to the next. This occurs by ubiquitin- ligases. The GI-S cyclins are destroyed by SCF (E3 ubiquitin-ligase) and M-phase cyclins by APC ( anaphase promoting factor), whch is another ubiquitin ligase. All Cdk activity ends and comes to zero after mitosis.

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