The Cell Cycle - G1 cyclins G1 cyclins bind to Cdk proteins...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
The Cell Cycle Cell Cycle Regulation Cyclin-Dependent Protein Kinase (Cdks) A Cdks is an enzyme that adds negatively charged phosphate groups to other molecules in a process called phosphorylation. Through phosphorylation, Cdks signal the cell that it is ready to pass into the next stage of the cell cycle. As their name suggests, Cyclin-Dependent Protein Kinases are dependent on cyclins, another class of regulatory proteins. Cyclins bind to Cdks, activating the Cdks to phosphorylate other molecules. Cyclins Cyclins are named such because they undergo a constant cycle of synthesis and degradation during cell division. When cyclins are synthesized, they act as an activating protein and bind to Cdks forming a cyclin-Cdk complex. This complex then acts as a signal to the cell to pass to the next cell cycle phase. Eventually, the cyclin degrades, deactivating the Cdk, thus signaling exit from a particular phase. There are two classes of cyclins: mitotic cyclins and G1 cyclins.
Background image of page 1
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: G1 cyclins G1 cyclins bind to Cdk proteins during G1. Once bound and activated, the Cdk signals the cell's exit from G1 and entry into S phase. When the cell reaches an appropriate size and the cellular environment is correct for DNA replication, the cyclins begin to degrade. G1 cyclin degradation deactivates the Cdk and leads to entry into S phase. Mitotic Cyclins Mitotic cyclins accumulate gradually during G2. Once they reach a high enough concentration, they can bind to Cdks. When mitotic cyclins bind to Cdks in G2, the resulting complex is known as Mitosis-promoting factor (MPF). This complex acts as the signal for the G2 cell to enter mitosis. Once the mitotic cyclin degrades, MPF is inactivated and the cell exits mitosis by dividing and re- entering G1. The cellular signals that we described earlier (cell size, completion of DNA replication, and cellular environment) provide the signals that regulate the synthesis and degradation of cyclins....
View Full Document

This note was uploaded on 01/27/2012 for the course BIOLOGY BSC1005 taught by Professor Rodriguez during the Winter '09 term at Broward College.

Ask a homework question - tutors are online