Question

What are internal and external regulators?

Answer 1

Internal regulators are proteins that react to changes within a cell. For example: The fact that a normal cell will not enter mitosis until its entire DNA has been replicated is regulated by a protein within the cell. This protein is an internal regulator. Mitosis is the biological term for the division of a mother cell into two daughter cells.

Answer 2

External regulators are also proteins, but they react to stimuli from outside the cell. They direct cells to either speed or slow the cell cycle based upon outside conditions. For example, one protein reacts to molecules on the outside of a neighboring cell. This helps make certain that cells stop dividing when overcrowded. That explains why, in a petri dish, cells will continue to grow and divide only until they have formed a thin layer along the bottom.