Lecture 15 - Cell Cycle Control

What is the S phase of the cell cycle?

The S phase is when DNA replication occurs.

What is the M phase of the cell cycle?

The M phase is when mitosis occurs.

What is the overarching concept of the cell cycle?

Cell division is tightly regulated.

What are the two main reasons for regulating the cell cycle?

To ensure there are enough resources for cells and to prevent cancer from mutations in DNA.

What are the criteria for passing the G1 checkpoint?

Cell size must be adequate, nutrients must be sufficient, social signals must be present, and DNA must be undamaged.

What must be checked at the G2 checkpoint?

Chromosomes must be replicated successfully, DNA must be undamaged, and activated MPF must be present.

What must be checked at the metaphase checkpoint?

Chromosomes must be attached to the spindle apparatus, properly segregated, and MPF must be absent

What is the G0 exit?

Differentiated cells exit the cell cycle to do specific functions in their tissue. They graduated and are going into the workforce.

Why is it important for a cell to be checked before dividing?

To prevent the propagation of mutations to new cells and maintain specific cell density (quota).

What signal promotes cell division?

growth factors stimulate cyclin and E2F

How does cyclin activate the cell cycle?

Cyclin phosphorylates with CDK(inase) enzyme while RB inactivates E2F, CDK then phosphorylates RB releasing E2F, E2F triggers production of S-phase proteins

What happens if DNA is damaged at checkpoint 1?

p53 bind to CDK inhibitor to signal cell division to stop causing DNA repair, senescence, or cell death

What is the correlation between P53 and cancer?

P53 triggers more cell death

What is the Hayflick limit?

The average number of times a normal human cell population will divide before becoming senescent and dying.

What role do telomeres play in the cell cycle?

Telomeres act as a buffer for chromosomes following DNA replication.

What happens when telomeres become too short?

Cells will no longer pass the cell cycle checkpoint 1, leading to cessation of division.

What is telomerase?

An enzyme that restores telomere length and maintains the replicative capacity of cells.

What is the function of P53 proteins in the cell cycle?

P53 proteins signal to stop cell division if DNA damage is present.

How do mutations affect cancer development?

Mutations can lead to unchecked cell proliferation, evasion of cell death, and increased genome instability.

What is the BRCA1 gene associated with?

The BRCA1 gene is associated with DNA damage repair; mutations increase the risk of cancer.

What are mutagens?

Agents that cause changes to DNA, leading to mutations.

What is nucleotide excision repair?

A DNA repair mechanism that fixes damaged DNA.

What is the role of cyclins in the cell cycle?

Cyclins activate CDKs, which are necessary for cell cycle progression.

What is MPF?

M Phase Promoting Factor, the active cyclin-CDK complex that initiates mitosis.

How does DNA polymerase contribute to DNA replication?

DNA polymerase synthesizes new DNA strands and can proofread to fix mismatches.

What is the significance of cell density in the cell cycle?

Maintaining specific cell density ensures the organism can meet resource demands.

What is the effect of UV light on cell division?

Exposure to UV light can reduce and stop cell division.

How do cancer cells differ from normal cells in terms of cell cycle regulation?

Cancer cells proliferate unchecked by cell cycle checkpoints and can evade programmed cell death.

What is the impact of taxol on cancer treatment?

Taxol destabilizes microtubules to stop cell division during M phase.

What is the role of growth factors in cell division?

Growth factors promote cell division by signaling cells to progress through the cell cycle.

What happens if a cell has DNA damage during the cell cycle?

The cell will not pass the checkpoints and will not divide.

What is the relationship between telomere shortening and species lifespan?

The rate of telomere shortening predicts the lifespan of a species.