MODIFIED from a slide show by Kim Foglia http://www.explorebiology.com/documents/37Ch12MitosisRegulation2005a.pdf

INTERPHASE = G1, S, G2

G1- Gap 1Grow by producing proteins & organelles

G2- Gap 2Grow Produce molecules & organelles needed for cell division

S- SynthesisDNA replication

Some can return to cycle with signal (Ex; Liver cells respond to injury)Some never divide again (Ex: Mature nerve, muscle cells)

MITOSIS

G0- Cell leaves cycle and stops dividingMost body cells in this phase

Cyclin-dependent kinases (Cdk’s) are present all the time but inactive unless combined with cyclins

Presence of MPF triggers passage past G1 & G 2 checkpoints

KINASES-Enzymes that workby adding a phosphate groupto other molecules

Cyclin levels change throughoutcell cycle

Fluctuating levels of different Cyclin-Cdk complexesseem to control all stages of cell cycle

CANCER CELLS• Don’t respond to control signals• Lose density-dependent inhibition• Lose anchorage dependence• Telomerase enzymes

maintain/replace telomeres

Transformation- process that changes a normal cell into a cancer cell

Telomeres protect DNA from being degraded

Telomeres become shorter with each replication; shorter in older cells

Telomerase enzyme lengthens telomeres

Cancer cells have increased telomerase activity

Jack Szostak Carol Greider Elizabeth Blackburn.

2009Nobel PrizePhysiology/MedicineDiscovery of Telomeres

Most cells divide 20-50 times in culture; then stop, age, die

Cancer cells are “immortal” -HeLa cells from a tumor removed from a woman (Henrietta Lacks) in 1951 are still reproducing in culture

http://www.sanger.ac.uk/Info/Press/gfx/081223_cells_300.jpg