Regulation of Cell Cycle (College Board AP® Biology): Study Guide

In order for cells to progress through the stages of the cell cycle, they must pass through a series of checkpoints; this ensures that:

• cells are large enough

• DNA has been replicated correctly

• necessary nutrients are available

Checkpoints can be controlled by the interactions between cyclins and cyclin-dependent kinases

• Cyclins:

  • are proteins, the levels of which change throughout the cell cycle

  • bind to cyclin-dependent kinases, producing complexes which trigger the next stage of the cell cycle

• Cyclin-dependent kinases:

  • are enzymes, present at the same concentration throughout the cell cycle

  • are inactive until they bind to cyclins

  • phosphorylate other molecules to activate them

Disruption of the cell cycle can result in:

• cancer or

• apoptosis

Cancer can develop due to uncontrolled cell division

• Mutations in protooncogenes can cause them to become oncogenes, resulting in increased expression of proteins that stimulate cell division

• Mutations in tumour suppressor genes can result in decreased expression of proteins that detect errors in DNA replication; this can lead to cell division in cells that contain DNA errors

Apoptosis is described as programmed cell death; it allows:

• the destruction of cells that contain dangerous mutations, such as those described above

• the removal of cells that are no longer needed during development, e.g. in embryos the fingers of the hand are joined together by webs of skin, but this skin is eventually removed by apoptosis