Cell Cycle Control and DNA Repair Proteins

Flashcards about cell cycle control, cell cycle arrest, and DNA repair proteins.

Rb

Inhibits the cell cycle by binding to E2F transcription factors, preventing transcription of genes required for S phase entry. It must be phosphorylated to release E2F and allow progression into the S phase.

Cyclin D-Cdk complex

Phosphorylates the Rb protein, leading to Rb inactivation and release of E2F, promoting progression into S phase in G1 phase

Cyclin E-Cdk complex

Further phosphorylates Rb and initiates DNA replication by activating S phase proteins, performs its function in late G1 phase

E2F

Transcription factor that activates genes required for DNA replication and S phase entry; inhibited by Rb when unphosphorylated

CDC6 protein complex

Helps load the MCM helicase onto DNA to form the pre-replication complex, ensuring DNA replication starts correctly. Functions in late G1 to the start of S phase

Cyclin A-Cdk complex

Activates DNA replication machinery and prevents re-replication of DNA within the same cycle and is in charge of phosphorylating CDC6. It functions primarily in S phase and continues into S phase

Cyclin B-Cdc complex

Triggers entry into mitosis by phosphorylating key proteins involved in chromosome condensation, nuclear envelope breakdown, and spindle formation

Ras

A GTPase that relays signals from growth factor receptors to activate the MAPK pathway, leading to increased transcription of cyclins (like Cyclin D) and promoting cell cycle entry (activated by GTP and activates RAF)

p53

Tumor suppressor protein that activates DNA repair genes, arrests the cell cycle (via p21), or induces apoptosis in response to DNA damage, functions in G1/S checkpoint, but can also act at G2/M checkpoint if damage is detected

p21

Inhibits cyclin-dependent kinases (CDKs) and prevents progression from G1 to S phase, serving as a checkpoint in response to DNA damage or stress signals (activated by p53) and functions in G1/S checkpoint (also active in G2/M if DNA damage is present)

Mdm2

This is a proto-oncogene that Inhibits p53 by promoting its degradation via ubiquitination. Regulates p53 levels, ensuring that p53 doesn’t accumulate in the absence of DNA damage, functions primarily during early G1

GADD45 and 14-3-3σ

Involved in DNA repair, checkpoint control, and apoptosis in response to DNA damage or stress; Regulates the G2/M transition, preventing premature mitosis by stabilizing Cyclin B-Cdk1 complexes

c-MYC

Transcription factor that promotes expression of genes for cell growth and division (e.g., cyclins, E2F). Receives signal from receptor. Drives G1 to S phase progression.

BRCA1 and BRCA2

DNA damage repair, especially homologous recombination; also regulates checkpoints (S and G2/M). Assists RAD51 in homologous recombination for DNA double-strand break repair.