Cell cycle Flashcards
What occurs during the G₁ phase of the cell cycle?
The cell grows in size, synthesizes proteins and organelles, and prepares for DNA replication. The G₁ checkpoint ensures the cell is ready to proceed.
What happens during the S phase of the cell cycle?
DNA replication occurs, doubling the genetic material. Each chromosome is duplicated into two sister chromatids.
What happens during the M phase?
The cell divides into two daughter cells. Mitosis (nuclear division) and cytokinesis (cytoplasm division) occur, with mitosis having five stages: Prophase, Prometaphase, Metaphase, Anaphase, and Telophase.
What occurs in the G₂ phase?
The cell continues to grow, producing proteins and organelles for mitosis. The G₂ checkpoint ensures DNA replication is complete and correct.
What is the G₀ phase?
A resting phase where some cells (e.g., neurons, muscle cells) remain metabolically active but do not divide. Cells in G₀ do not proceed with division.
What is the difference between senescence and quiescence?
Quiescence is a reversible cell cycle arrest (G₀ phase), where cells are inactive but can re-enter the cycle under favorable conditions. Senescent cells, on the other hand, cannot divide and often exhibit changes like the secretion of inflammatory factors.
What is cellular senescence?
A permanent cell cycle arrest where cells lose the ability to divide, often due to stress, DNA damage, or oncogene activation. It plays a role in aging and cancer prevention but can contribute to age-related diseases.
How is the activity of cyclin-CDK complexes regulated?
Cyclin binding to CDKs activates them, but inhibitory proteins like p21 and p16 can block their function. Additionally, phosphorylation by kinases and dephosphorylation by phosphatases control their activation.
What does p53 do in response to cellular stress?
p53 acts as a transcription factor that halts the cell cycle in response to stress (e.g., DNA damage) by inducing the expression of p21, which inhibits CDKs. This prevents the cell from entering S phase.
How does Mdm2 regulate p53?
Mdm2 inhibits p53 by binding to it and promoting its degradation via ubiquitination. This controls p53 levels and ensures the cell cycle can progress when conditions are favorable.
What role do cyclins and CDKs play in the cell cycle?
Cyclins activate CDKs (cyclin-dependent kinases), which drive the progression through different cell cycle phases. CDKs are inactive without cyclins and are regulated by phosphorylation and dephosphorylation.
What is the restriction point in the G₁ phase?
The restriction point is a checkpoint in G₁ that controls entry into the S phase. It is regulated by the pRB protein, which prevents progression unless it is phosphorylated, allowing E2F to activate DNA replication.
Which cyclins are involved in the regulation of the cell cycle phases?
Cyclin D: Drives G₁ phase (activates CDK4/CDK6).
Cyclin E: Drives G₁ to S phase transition (activates CDK2).
Cyclin A: Drives S phase (activates CDK2).
Cyclin B: Drives G₂ to M phase transition (activates CDK1).
What is the role of pRB in cell cycle regulation?
pRB prevents progression from G₁ to S phase by inhibiting E2F transcription factors. When pRB is phosphorylated by cyclin-CDK complexes, it releases E2F, allowing entry into S phase.
What are the key cell cycle checkpoints?
G₁/S checkpoint (Restriction point): Ensures the cell is ready to replicate DNA.
G₂/M checkpoint: Ensures DNA replication is complete and correct.
M Checkpoint: Ensures chromosomes are properly aligned before division.
