Cell Cycle Control System Chapter 12.3

Simon Says!! Its Time to Play Simon says stand up. Simon says find a partner. Sit down. Simon says connect shoulder to shoulder with your partner. Simon says separate or divide from your partner. Multiply.

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 arises Nerve and muscle cells don’t even divide

Cytoplasmic signals 1970s experiments revealed that molecular signals from the cytoplasm were driving the cell cycle.

Cell Cycle Control System A cyclically operating set of molecules in the cell that both triggers and coordinates key events in the cell cycle.

Other Examples Take a minute. Can you think of more examples of control systems?

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

Checkpoints Three major checkpoints: G1 – the restriction point G2 –MPF facilitates to cell dividing stage M – mitotic division

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

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

External Checkpoints Growth 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

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.

Cancer Cells Transformation – process that converts a normal cell to a cancer cell Tumors: benign – remains at original site malignant – invades other organs and impairs function

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

Treatments Radiation – 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