Subtitle Cell Cycle Regulation

Timing and rate of cell division are important Rate of cell division varies depending on cell type Cell cycle is controlled by proteins and enzymes Normal Cell Cycle

Cell cycle in eukaryotes is driven by a combination of cyclins and cyclin-dependent kinases (CDKs) Different cyclin/CDK combinations control different activities at different stages in the cell cycle Role of Cyclins

Beginning and end of the cell cycle are signaled by the combination of cyclin with CDK Cyclin/CDK combinations signal DNA replication, protein synthesis, and nuclear division Role of Cyclins (continued)

Cell cycle has built-in checkpoints that monitor the cycle and can stop it if something goes wrong Examples – checkpoint near the end of G 1 monitors for DNA damage and can stop the cycle before entering the S phase spindle checkpoints in mitosis checks for failure of spindle fibers and can stop the cycle before cytokinesis Quality Control Checkpoints

Cancer – the uncontrolled growth and division of cells – a failure of regulation of the cell cycle Cancer cells spend less time in interphase than normal cells Abnormal Cell Cycle: Cancer

Various environmental factors can affect the occurrence of cancer cells Substances and agents that are known to cause cancer are called carcinogens Causes of Cancer

Asbestos Tobacco Radiation – UV rays, X- rays Carcinogens

More than 1 change in DNA is required to change an abnormal cell into a cancer cell It is possible to have many changes in DNA over time Risk for cancer increases with age Cancer Genetics

Apoptosis – programmed cell death Cells shrink and shrivel in a controlled process Occurs during the development of the human hand and foot Also occurs in cells that are damaged beyond repair Can help protect organisms from developing cancerous growths Apoptosis

unspecialized cells that can develop into specialized cells when under the right conditions 2 basic types – embryonic stem cells, adult stem cells Stem Cells

Embryonic Stem Cells – mass of 100 – 150 cells that result after a sperm fertilizes an egg Adult Stem Cells – found in various tissues in the body; might be used to maintain and repair the same kind of tissue in which they are found Stem Cells