Fill in the blank: Word Bank:

Cyclins, Inactivation, Skin, Cancer, Chromatids, Nerve

In multicellular organisms, cell growth and division is very controlled. Some cells like muscle and cells stop dividing after maturity. Other cells like and blood cells grow and divide rapidly through life. are proteins that regulate the timing of the cell cycle, "telling" the cell when to divide. If cells stop responding to regulation, uncontrolled cell growth can lead to .