1. The Cell Cycle 5.1

2. 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?

3. 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.

4. 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.

5. 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

6. 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)

7. 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)

9. Cell Cycle Demo

10. 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