Regulating the Cell Cycle

Cell Division Rates

• Cells do not all reproduce at the same rates

• Stomach cells, skin cells, blood cells and others reproduce often

• Nerve cells and most muscle cells do not reproduce at all once they are mature

Cell Division Rates

• Many major medical issues that are being currently solved are related to cell reproduction– Cancer (Uncontrolled

Cell Reproduction)– Stem Cells (Cell

reproduction to damaged cells)

Cell Cycle Regulators

• There are two different types of regulators that help a cell know when it is time to replicate– Internal regulators– External regulators

Controls on Cell Division• Scientists can observe cell

division in Petri dishes containing different types of agar– This gives cells the food they

need to complete their cell cycles

• Cells on a Petri dish will grow until they form a thin layer– The cells will grow and divide

until they come in contact with other cells

– When this happens they will stop growing

Controls on Cell Division

• If you take a full agar plate, and swipe away a section in the middle, what might happen?

• The cells will grow outward from the middle

• They will stop once they touch other cells

Controls on Cell Division• This means that cells have

the ability to turn on and turn off their cell division

• When you get a cut, the cells grow inward to close the cut

• The process of being cut starts the process of being healed by activating these mechanisms

Controls on Cell Division

• The same thing happens when bones break

• It is a more complex process than a cut, but it works on the same principals

• When bones break there is a separation between different types of cells that send signals to different tissues that action is needed

Cell Cycle Regulators• Many different proteins

combine to help control cell division

• First major proteins found in the 1950’s were cyclins

• During cell reproductions, cyclin levels are higher

• During interphase, cyclin levels are lower

Experiment

Cell Cycle Regulators

• Proteins that respond to outside environmental factors are external regulators

• Growth factors are an example of external regulators– They are proteins or

steroids that stimulate cell growth and division

• Other molecules slow down cell growth

Uncontrolled Cell Growth• Cancer is a disorder of

uncontrolled cell growth– Cancer cells don’t often

respond to signals that regulate the growth of most cells

– They form masses of cells called tumors

• Cancer cells can break loose and spread throughout the body

Uncontrolled Cell Growth

• Various forms of cancer have been linked to smoking, radiation exposure and viral infections

• All cancer cells however have one thing in common– The uncontrolled

reproduction of cell division

Uncontrolled Cell Growth• Many cancers can be caused

by a defective gene called p53– p53 normally halts the cell

cycle until all chromosomes have been replicated

• The p53 gene make a cell undergo apoptosis

• Apoptosis is a form of self destruction for the cell