mcb104 _101-106_ week 9

mcb104 _101-106_ week 9 - C ELL CYCLE Cyclin specific class...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
CELL CYCLE Cyclin —specific class of proteins that are expressed at different stages of the cell cycle. Activate cyclin dependent kinases. Cyclin-dependent kinase —expression is generally constant, but is active only when bound to a cyclin, so it’s activity is in a specific part of the cell cycle. Phosphorylation by a cdk is reversible. A single cdk can bind different cyclins, depending on which stage of the cell cycle it is. Ubiquitin —a small protein that is added to another protein that signals that protein to be degraded by the proteasome. Degradation by the proteasome is irreversible. Ubiquitin ligase —(also called E3) adds on ubiquitins to other proteins, targeting t them for degredation. Examples: anaphase promoting complex (APC), SCF. Mitosis Promoting Factor (MPF) Protein Kinase with two subunits o Cdk1- cyclin dependint kinase: induces mitosis through phosphorylation o Cyclin B: the regulatory subunit that activates Cdk1. How was it first identified? Researchers fused an M-phase cell and a G1 phase cell and observed that the chromosomes from the G1 cell suddenly condensed, indicating that something in the cytosol could drive mitosis. Likewise, injecting a frog egg’s cytoplasm from an M- phase egg could induce mitosis in an interphase egg. How was it first determined that its protein levels cycled with the cell  cycle? Tim Hunt injected radioactive 35 S-methionine into the cell. Unlike other proteins that persisted throughout the cell cycle, cyclins appeared in M-phase and were not present in interphase. How is MPF regulated? o Cyclin B protein levels o Phosphorylation of Cdk1 by Wee1, Cak, and Cdc25 (review the mechanism) Two general mechanisms for negative regulation of proteins involved in the cell cycle 1) Phosphorylation Happens fast and is reversible 2) Degradation Occurs through polyubiquitination and is irreversible Genetic screens in Yeast to identify genes important for cell cycle regulation
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Review important features of a temperature sensitive screen and how this technique was applied to identify cell cycle control mutants. What 
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 01/28/2010 for the course MCB 104 taught by Professor Urnov during the Fall '09 term at Berkeley.

Page1 / 5

mcb104 _101-106_ week 9 - C ELL CYCLE Cyclin specific class...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online