CELL CYCLE LIFE OF A CELL Most cells in the body are called somatic cells. These cells go through a series of stages called the cell cycle. Most of the cell’s life is spent in interphase (a phase of growth and normal functioning). A portion of its life is spent in cell division. Only happens in eukaryotes THE CELL CYCLE The four stages of the cell cycle are: G1 - Growth S - DNA replicates G2 - Growth M - Mitosis (cell divides) CHECKPOINTS The cell cycle has a series of checkpoints- cell cycle control system. Checkpoints are controlled by proteins. 3 Checkpoints: G1- Checks for normal growth G2- Checks for proper DNA synthesis M- Checks for proper attachment in mitosis before cells are pulled apart. If any of these checkpoints fail apoptosis (programmed cell death) HOW DO CHECKPOINTS WORK? There are a series of proteins called cyclindependent kinase. These enzymes wait for a signal from the cell and then activate the cell cycle. Signal is in the form of a protein (usually) WHAT CAN GO WRONG? At any point in the cycle, the cell could malfunction. If it does not pass a checkpoint, it either dies or goes into a permanent resting state. If the checkpoint system malfunctions, cells divide uncontrollably Tumors (Cancer)!