The Internal and External Factors that Influence the Cell Control System

Cyclins are the proteins that regulate the cell cycle. These proteins are used for Internal and External Regulators.
Internal Regulators are a group of proteins that respond to things happening inside the cell. These regulators allow the cell cycle to proceed but only when each stage has been competed. For example, one regulatory protein prevents the cell from entering Anaphase until the spindle fibers have attached the chromosome.

External Regulators are proteins that respond to events outside the cell. These regulators decide whether the cell cycle needs to speed up or slow down. One group of external regulatory proteins are called Growth Factors which stimulate the growth and division of the cell.

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