MICROANATOMY

Detailed explanation-1: -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.

Detailed explanation-2: -Cdks, cyclins, and the APC/C are direct regulators of cell cycle transitions, but they aren’t always in the driver’s seat. Instead, they respond to cues from inside and outside the cell. These cues influence activity of the core regulators to determine whether the cell moves forward in the cell cycle.