The Cell Cycle 5.1

Background Knowledge Answer the following questions: 1. How many cells do you think your body has? 2. Why does your body need to have a lot of cells? Each of us began as a single cell, so one important question is: 3. How did that single cell develop into a body with more than a trillion cells?

I. The 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.

II. Cell Division Cell division, also called cell reproduction, occurs in humans and other organisms at different times in their life. - Multi-cellular organisms grow by increasing the number of their cells. - Cell division replaces worn out or damaged cells.

III. The Cell Cycle Period in which a cell grows, prepares to divide, and then divides Consists of 3 main stages: 1. interphase – the longest period 2. mitosis – nuclear division 3. cytokinesis – cytoplasm division

III. The Cell Cycle Interphase consists of 3 stages: (Checkpoint) G1 - Cell Grows (Checkpoint) S - Genetic Material replicates G2 - Cell Grows - prepares for mitosis (Checkpoint)

IV. Checkpoints Control of the cell cycle occurs with a series of checkpoints – (cell cycle control system) 3 Checkpoints: G1 - Checks for normal growth – decides whether the cell will divide. G2 - Checks for proper DNA synthesis M - Checks for proper attachment in mitosis before cells are pulled apart – triggers the exit from mitosis If any of these checkpoints fail  apoptosis (programmed cell death)

Cell Cycle Demo http://www.cellsalive.com/cell_cycle.htm

V. 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. Cancer – a disease that occurs when the cell cycle is no longer regulated