4.7 Regulation of the Cell Cycle

Heritable information provides continuity of life. Describe the role of checkpoints in regulating the cell cycle. A number of internal controls or checkpoints regulate progression through the cycle. Interactions between cyclins and cyclin-dependent kinases control the cell cycle. Describe the effects of disruptions to the cell cycle on the cell or organism. Disruptions to the cell cycle may result in cancer and/or programmed cell death (apoptosis).

control/regulation of the cell cycle is key to proper growth, repair, and reproduction

may be done via cyclins and cyclin-dependent kinases

cyclin-dependent kinases

• present throughout the cell cycle at different checkpoints

• add phosphate groups to activate other molecules

• inactive itself until bound to cyclin proteins, becoming a mitosis-promoting factor

• levels of cyclin proteins vary, reaching their max just before mitosis

checkpoints

• G1 - checks if DNA is damaged; if so, cell exits cycle

• G2 - checks if DNA is replicated correctly

• M (after metaphase) - checks that chromosomes are properly attached to spindle

density-dependent inhibition

cells in tissues become too crowded, causing the cells to stop dividing

anchorage dependence

cells must be attached to surface to divide

proto-oncogenes

accelerate division at a specific rate

• mutation converts proto-oncogenes to oncogenes, promoting high rates of cell divisions and cancer

mutation of proto-oncogenes

• starts due to carcinogens (tobacco, UV rays, drugs, etc.)

• may be detected by tumor suppressor genes; mutated tumor suppressor genes allow cells to continue to divide and form tumors

• normal cells eventually go through apoptosis and die, unlike cancer cells