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Cell Cycle Control System
Chapter 12.3
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Its Time to
Play
Simon Says!!
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Molecular Control system
• Timing and rate of cell division in different parts of the plant and animal are crucial to normal growth, development, and maintenance.
• Frequency varies among different types of cells– Ex: Frequent divisions of skin cells
Liver cells reserve as need arisesNerve and muscle cells don’t even divide
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Cytoplasmic signals
• 1970s experiments revealed that molecular signals from the cytoplasm were driving the cell cycle.
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Cell Cycle Control System
A cyclically operating set of molecules in the cell that both triggers and coordinates key events in the cell cycle.
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Other Examples
• Take a minute. Can you think of more examples of control systems?
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Cycle Control System
• Checkpoints are critical control points where stop and go ahead signals regulate the cycle.
• Some cells have built in stop signals that halt the cycle until another signal overrides and starts cycle.
• Checkpoints can register signals from both inside and outside the cell
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Checkpoints
• Three major checkpoints:G1 – the restriction pointG2 –MPF facilitates to cell dividing stageM – mitotic division
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Regulatory Molecules
• Protein kinases enzymes that activate or inactivate proteins by phosphorylating them
• Cyclins are proteins that cyclically fluctuate their concentration in the cell
*determine active or inactive state of kinases.
• CdK – cyclin-dependent kinases in varying numbers control all stages of cell cycle
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Internal Checkpoints
• G1 phase – activator CdK will cause cycle to complete itself; whereas lack of cyclins will halt in G0 phase
• G2 phase – MPF “ M-phase promoting factor” will trigger passage to mitosis or cell dividing phase.
• M phase – kinetochores send signal that delays anaphase until all chromosomes are attached to spindle
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External CheckpointsGrowth factors – protein released by cells that stimulate
other cells to divide*mitogen – mitosis promoter
PDGF – made by platelets; required for division of fibroblasts to clot
(G1 phase)Density dependent inhibition – occurs when crowded cells
stop dividing*results from physical contact, and lack of
adequate growth factors and nutrients Anchorage dependence – cells must be attached to a
substratum such as extracelluar matrix; cytoskeleton attachment
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Cancer Cells• Cancer cells divide
excessively and invade other tissues.
• Cancer cell do not respond to most of the body’s control mechanisms.
• Cancer cell still grow even when growth factors have been depleted.
• Cancer cells stop dividing at random points of the cycle.
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Cancer CellsTransformation – process that converts a normal cell to a cancer cellTumors:
benign – remains at original sitemalignant – invades other organs and impairs
function
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Cancer Cells
Metastasis- spread of cancer cells to locations distant from original site.
*cells can secrete signal molecules that cause blood vessels to grow toward tumor*cells can also separate and travel in blood and lymph to other parts of the body
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TreatmentsRadiation – localized tumors or proliferation
*targets and damages DNA of cancer cell
Chemotherapy – malignant or metastasis*most target and prevent cells from proceeding past metaphase
*side effects – exerts same targets on normal cells Ex: intestinal cells - nausea hair follicle cells – hair loss immune cells - increased infections