Regulation of cell cycle

1. Cyclin-Cdk complex: Inside the cell, the cyclin-cdk complex regulates the changes in various stages of the cell cycle.
2. Cyclin-Cdk-MPF complex: MPF binds to the cyclin-cdk complex of the dividing cell to initiate the cell cycle.
3. P⁵³ protein: When DNA is damaged for some reason, P⁵³ protein stops the cell cycle. When DNA is extensively damaged, the P⁵³ protein induces cell death by apoptosis.
4. P²⁷ protein: P²⁷ protein binds to the cyclin-cdk complex and prevents cells from entering the confluent state. High levels of P²⁷ protein in cells cause breast cancer in women.
5. Cyclin: The regulator of cell cycle is cyclin protein. Timothy Hunt (1982) discovered cyclin proteins. For this, Timothy Hunt, Lee Hartwell and Paul Nurse were awarded the Nobel Prize in 2001. There are four types of cyclins in human cells.

(i) Cyclin-D: Cyclin-D transports cells from G1 to S phase and from S phase to G₂ phase.

(ii) Cyclin-E: Cyclin-E prepares the cell for DNA replication in S phase.

(iii) Cyclin-A: Cyclin-A activates and accelerates DNA replication in the S phase of the cell.

(iv) Cyclin-B: Cyclin-B performs spindle fibers and other essential functions for mitosis.