Lecture 43: Cell proliferation- Mitotic signals Flashcards
(41 cards)
What is the purpose of the cell cycle?
To ensure accurate duplication and division of the genome and cellular contents between daughter cells in an orderly and regulated manner.
What are the four main phases of the cell cycle?
G1 (growth), S (DNA synthesis), G2 (preparation for mitosis), M (mitosis).
What is the quiescent phase of the cell cycle?
G0 phase – a reversible, non-dividing state where cells can exit the cycle in response to environmental signals.
When do most mammalian cells enter G0?
From the G1 phase, particularly in mature tissues with low proliferation rates.
What allows cells to re-enter the cell cycle from G0?
Mitogenic (growth) signals like EGF, which initiate signaling cascades promoting cyclin/CDK expression.
How does nutrient availability affect cell cycle speed in yeast?
In glucose medium: ~1.5h doubling time. In galactose: ~3.5h. Conditions like nutrient type affect cycle speed.
What is the lag phase in yeast culture growth?
Initial phase where cells adapt to new conditions without dividing.
What is the exponential phase?
Period of rapid cell division at a constant rate, reflecting the cell cycle’s natural speed.
What is the retardation phase?
Slowing growth due to accumulation of waste or depletion of nutrients.
What is the stationary phase?
Cells stop dividing and can enter quiescence, but may re-enter the cycle if placed in fresh media.
What are cyclins and what is their role?
Cyclins are regulatory proteins whose levels fluctuate to drive cell cycle progression by activating CDKs.
What are CDKs?
Cyclin-dependent kinases – enzymes that require binding to a cyclin to phosphorylate target proteins for cycle progression.
How do cyclin-CDK complexes drive the cell cycle?
They phosphorylate substrates needed to initiate each phase transition (e.g., DNA replication, mitosis).
Name two cyclins involved in G1 progression.
Cyclin D and Cyclin E.
Which CDKs pair with G1 cyclins?
CDK4, CDK6 (with Cyclin D) and CDK2 (with Cyclin E).
What are G0 cells?
Cells that have exited the cycle and are not actively dividing, often differentiated or temporarily inactive.
Name some examples of cells permanently in G0.
Eye lens cells, neurons, and some muscle cells.
Are G0 cells metabolically inactive?
No. They can be active in function (e.g., producing proteins) but not dividing.
What is the clinical importance of G0 in wound healing?
Fibroblasts re-enter the cycle from G0 to repair tissue.
How is the immune system linked to G0?
Lymphocytes in G0 can be activated to divide rapidly during immune responses.
What is a mitogen?
A signal (e.g., growth factor like EGF) that stimulates cell cycle re-entry from G0.
Where do growth signals begin?
At the plasma membrane via binding of ligands (e.g. EGF) to receptors (e.g. EGFR).
What happens when EGFR binds EGF?
Receptor dimerises, autophosphorylates, and activates intracellular signaling cascades.
What is Ras and what does it do?
A membrane-bound GTPase recruited by adaptor proteins to initiate MAPK cascade.
