Cell Cycle and regulation Flashcards
What regulates transitions between phases of the cell cycle?→
Cyclins, cyclin-dependent kinases (CDKs), and tumor suppressors
What are the main phases included in the M phase of the cell cycle?→
Prophase, prometaphase, metaphase, anaphase, telophase, and cytokinesis
What are cyclin-dependent kinases (CDKs)?→
Constitutively expressed enzymes that are inactive unless bound to cyclins
What are cyclin-CDK complexes?→
Cyclins are phase-specific regulatory proteins that activate CDKs when stimulated by growth factors
What is the role of the cyclin-CDK complex?→
Phosphorylates other proteins (e.g., Rb) to coordinate cell cycle progression
How does p53 act as a tumor suppressor in the cell cycle?→
Induces p21 → inhibits CDK → hypophosphorylates Rb → inhibits G1 to S progression
What happens when tumor suppressor genes are mutated?→
Unrestrained cell division, e.g., in Li-Fraumeni syndrome
Which growth factors stimulate transition from G1 to S phase?→
Insulin, PDGF, EPO, EGF (via tyrosine kinase receptors)
What are permanent cells and what is their cell cycle status?→
Remain in G0 and regenerate from stem cells (e.g., neurons, skeletal/cardiac muscle, RBCs)
What are stable (quiescent) cells and how do they behave in the cell cycle?→
Enter G1 from G0 when stimulated (e.g., hepatocytes, lymphocytes, PCT cells, periosteal cells)
What are labile cells and how do they behave in the cell cycle?→
Never go to G0, divide rapidly with a short G1 (e.g., bone marrow, skin, gut epithelium, hair follicles, germ cells)
Which type of cells are most affected by chemotherapy?→
Labile cells
What leads to cell cycle arrest in response to DNA damage?→
p53 → p21 → inhibition of cyclin-CDK → cell cycle arrest
How does p53 induce apoptosis when DNA damage is severe?→
Via BAX/BAK → caspase activation → intrinsic apoptosis pathway
How does HPV E6 affect the cell cycle?→
Degrades p53, preventing apoptosis
What role does Rb play in gene transcription?→
Hypophosphorylated Rb binds E2F and inhibits transcription; phosphorylated Rb releases E2F → gene transcription
