Cell Cycle Control System - Cell Bio Lecture 20

Cell-cycle control system

A complex network of regulatory proteins that governs the orderly progression of the cell through the phases of the cell cycle.

Cell-cycle checkpoints

Specific points in the cell cycle where the process is halted until certain conditions are met, ensuring accurate DNA replication and chromosome segregation.

Cyclin-dependent kinases (Cdks)

A family of protein kinases that are active only when bound to regulatory subunits called cyclins, driving the cell cycle forward.

Cyclin

A regulatory protein whose concentration fluctuates cyclically throughout the cell cycle and that binds to and activates specific Cdks.

G1-Cdk

A cyclin-Cdk complex that is active during the G1 phase and helps to regulate progression through this phase.

G1/S-Cdk

A cyclin-Cdk complex that is activated at the end of G1 and triggers entry into the S phase, promoting DNA replication.

S-Cdk

A cyclin-Cdk complex that is active during the S phase and is essential for the initiation and completion of DNA replication.

M-Cdk

A cyclin-Cdk complex that is activated at the beginning of M phase and drives entry into mitosis by phosphorylating various target proteins.

APC/C anaphase promoting complex

A ubiquitin ligase that triggers the separation of sister chromatids during anaphase and promotes the degradation of M-cyclins, leading to exit from mitosis.

Ubiquitin

A small protein that, when attached in chains to other proteins, marks them for degradation by the proteasome.

Ubiquitin-proteosome system

A major cellular machinery for protein degradation, involving the tagging of target proteins with ubiquitin and their subsequent breakdown by the proteasome.

Proteolysis

The breakdown of proteins into smaller polypeptides or amino acids.

Inhibitory phosphates

Phosphate groups added to Cdks by Wee1 kinase that prevent their activation.

Inhibitory kinase Wee1

A protein kinase that phosphorylates and inhibits M-Cdk and other Cdks.

Activating phosphatase Cdc25

A protein phosphatase that removes inhibitory phosphates from Cdks, leading to their activation.

T-loop

A regulatory structure in the Cdk catalytic subunit that, when phosphorylated by CAK, allows for full Cdk activity.

Cdk-activating kinase (CAK)

A protein kinase that phosphorylates a threonine residue in the T-loop of Cdks, leading to their full activation.

Cdc inhibitor proteins (CKIs)

A family of proteins that bind to and inhibit Cdk activity, helping to regulate cell cycle progression.

p27 protein

A CKI protein that can inhibit G1/S-Cdk and S-Cdk, helping to arrest the cell cycle in G1.

Protein Phosphatase 2A (PP2A)

A phosphatase that can counteract the activity of Cdks by removing phosphate groups from their target proteins.

Terminal differentiation

The process by which a cell becomes highly specialized and permanently stops dividing.

Mitogens

Extracellular signaling molecules that stimulate cell division, primarily by overcoming cell cycle checkpoints in G1.

E2F protein

A transcription factor that activates the expression of genes required for S phase entry and DNA replication, often inhibited by Rb protein.

Retinoblastoma (Rb) protein

A tumor suppressor protein that binds to and inhibits E2F transcription factors, preventing premature entry into S phase.

Tumor suppressors

Genes whose protein products normally inhibit cell proliferation; mutations that inactivate these genes can contribute to cancer.

p53 protein

A tumor suppressor protein that is activated in response to DNA damage and can induce cell cycle arrest, DNA repair, or apoptosis.

p21 protein

A CKI protein whose transcription is activated by p53; Can inhibit G1/S-Cdk and S-Cdk, arresting the cell cycle in response to DNA damage.

Apoptosis

Programmed cell death, a tightly regulated process that eliminates unwanted or damaged cells.

Origin of replication

A specific sequence of DNA where DNA replication initiates.

Origin recognition complexes (ORCs)

A protein complex that binds to replication origins and serves as a platform for the assembly of the pre-replicative complex.

Pre-replicative complex (pre-RC)

A protein complex that assembles at replication origins during G1 and is required for the initiation of DNA replication in S phase.

Cdc6 (cell division cycle 6)

A protein that binds to ORC and helps to load a helicase onto DNA to form the pre-replicative complex.