.Cell Division- Regulation of the

Cell Cycle

Target #25-I can explain the external factors that are involved in cell cycle

regulation• Both external and internal factors regulate the cell cycle in

eukaryotic cells• External Factors

– Physical signals cell to cell contact– Chemical signals

• Growth factors: a broad group of proteins that stimulate cell division– Bind to receptors that activate specific genes to

trigger cell growth– Specific growth factors exist for different cell types

» Ex: erythropoietin is a growth factor that produces more red blood cells

• Hormones: stimulate growth of certain cell types– Ex: growth hormone results in bone growth and

affects protein and fat metabolism

Target #26- I can explain the Internal factors that are involved in cell cycle

regulation• Two prominent internal factors, kinases

and cyclins, help cells advance to the next stage of the cell cycle when a cell stops dividing– Kinase: an enzyme that, when activated,

transfers a phosphate group from one molecule to a target molecule• Increases the energy in the target

molecule– Cyclins: a group of proteins that trigger

kinases

• Apoptosis: programmed cell death– Occurs when internal or external signals

activate genes that help produce self-destructive enzymes• The nucleus breaks apart• Immune cells “eat”, or break down,

the apoptotic cell

Target #27: I can describe the characteristics of cancer

• Cancer: the common name for a class of diseases characterized by uncontrolled cell division– Arises when regulation of

the cell cycle breaks down– Cells will divide in the

absence of growth factors required for division• Divide more often

– Cancer cells form disorganized clumps called tumors• Can be benign (not harmful) or

malignant (harmful)