10-3: Regulating the cell cycle10-3: Regulating the cell cycle

Cardiac cells Small intestineSmooth muscle

Nerve cell: brain

Cardiac: cannot divideSmooth muscle: can divideIntestine: 1-2 days, can divideNerve cell: cannot divideRBC: 120 days, cannot divide

Red blood cell

Specialized cells divide at different ratesSome cells never divide

Controls on cell divisionControls on cell division

► Not all cells in the Not all cells in the body divide at the body divide at the same same raterate

► Cells in a petri dish will Cells in a petri dish will divide until they fill the divide until they fill the dish, then they stop.dish, then they stop.

► If cells are removed, If cells are removed, they’ll grow until the they’ll grow until the space is filled again.space is filled again.

► Controls on cell Controls on cell division can be turned division can be turned on and off.on and off.

Cell Cell cycle cycle

regulatorregulatorss

► The protein cyclin regulates the timing of the cell cycle in eukaryotic cells. When present, cyclin triggers cell division.

Internal regulatorsInternal regulators► Proteins that

respond to internal events in the cell.

► Some make sure that the cell doesn’t enter mitosis until the DNA is replicated

► Another makes sure that chromosomes are attached to the spindle before anaphase.

Different cyclins active at phases of thecell cycle

External External regulatorsregulators► Proteins that Proteins that

respond to events respond to events outsideoutside the cell. the cell.

► Direct the cell to Direct the cell to speed upspeed up or or slow slow downdown the cell cycle. the cell cycle.

► Growth regulators: Growth regulators: important in important in embryos, for embryos, for healing woundshealing wounds

Rubber bullet wound

Cat embryo

Inhibitors on cell surfaces cause cells to Inhibitors on cell surfaces cause cells to slow or stop divisionslow or stop division

Uncontrolled Uncontrolled cell growthcell growth

► Cancer is a disease of Cancer is a disease of the cell cyclethe cell cycle

► Cancer cells don’t Cancer cells don’t respond to the signals respond to the signals that regulate growth. that regulate growth.

► Leads to Leads to uncontrolled uncontrolled cell growthcell growth..

► Causes: viruses, Causes: viruses, tobacco, radiation tobacco, radiation exposureexposure

► Form masses of cells: Form masses of cells: tumorstumors

Oral cancer

Melanoma: skin cancer

Stem cellsStem cells► UnspecializedUnspecialized cells cells

that have the that have the ability to turn into ability to turn into any kind of cell.any kind of cell.

► Could replace Could replace damaged cells of damaged cells of brain, nervous brain, nervous system.system.

Human stem cell

stem cell controversystem cell controversy► Stem cells are produced from human embryos, and Stem cells are produced from human embryos, and

are destroyed when used for researchare destroyed when used for research► Raises moral and ethical questions as to their use: Raises moral and ethical questions as to their use:

Is a fertilized egg a human being?Is a fertilized egg a human being?

Stem cells in umbilical cord blood

Human blastocyte: 100 cells

Adult stem Adult stem cellscells

► Adult stem cells are Adult stem cells are found in bone marrowfound in bone marrow

► Future possibilityFuture possibility: a : a person’s person’s own stem own stem cellscells could be used to could be used to heal previously heal previously untreatable untreatable conditions: spinal conditions: spinal cord injury, grow new cord injury, grow new liver tissue, replace liver tissue, replace heart valves, reverse heart valves, reverse the effects of the effects of diabetes.diabetes.