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5.3 Regulation of the Cell Cycle
LEQ: Why is the eukaryotic cell cycle regulated?
• Key terms: cyclin, growth factor, kinase
• Reading 5.3 (cancer)
5.3 Regulation of the Cell Cycle
• Activator:
• Briefly explain why the daughter cells resulting from
mitosis are genetically identical to each other and to the
original parent cell.
5.3 Regulation of the Cell Cycle
Cells respond to internal and external signals that
regulate cell division.
• Cell communication:
• physical contact with cells
• Cell signaling:
– Receptors/enzymes
– soluble chemical signals:
- Growth factors
- Survival signals
5.3 Regulation of the Cell Cycle
Internal and external factors: Example
• Cell adhesion (stops cycle)
– Positional information to nucleus
– integrins
5.3 Regulation of the Cell Cycle
All cells rely on cell signaling to detect and respond to
cues in their environment:
– Receptor Tyrosine Kinase (RTKs) activation involves
binding to a signal (ligand), the joining together and
phosphorylation of proteins.
– Growth promoting
5.3 Regulation of the Cell Cycle
Signaling pathways
• Prevent division or,
• Promote cell division:
– Ras pathways
promote cell division
by turning on
genes/proteins
associated with the
cell cycle
5.3 Regulation of the Cell Cycle
Cdks coordinate passage through checkpoints:
• Checkpoints:
– G1/S
- Restriction/ enter S
– G2/M
- Enter M
– Spindle/metaphase
- Exit M
5.3 Regulation of the Cell Cycle
• Cyclins activate Cdks
• Timing of each phase can be
adjusted
• Failure/DNA damage can result
in cell death.
– apoptosis
5.3 Regulation of the Cell Cycle
• Cell cycles can vary based on stages of development
5.3 Regulation of the Cell Cycle
Programmed cell death purges damaged cells to prevent
disease and shape development
• Apoptosis is programmed cell death:
– Initiation of “death” proteins (caspases)
- self-destructive enzymes
– Results in progressive cell destruction
- animation
5.3 Regulation of the Cell Cycle
Pair Question:
• Suppose a mutation in a Cdk gene causes the Cdk
protein to change shape so it spontaneously activates
without the aid of cyclins. Predict what would happen to
the cell.
• Suppose a mutation in a caspase gene causes a
Caspase protein to change shape so it spontaneously
activates without the aid of a signaling molecule. Predict
what would happen to the cell.
5.3 Regulation of the Cell Cycle
• Competition in a tissue for growth factors “sculpts” a
tissue
– Loss of “tails”
– Finger webbing
webbed fingers
5.3 Regulation of the Cell Cycle
• Leaf senescence (fall) is programmed cell death!
• Leaf development is programmed, seasonal cell growth!
5.3 Regulation of the Cell Cycle
Telomere shortening leads to senescence and
programmed cell death
5.3 Regulation of the Cell Cycle