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 period2. mitosis – nuclear division3. cytokinesis – cytoplasm

division

III. The Cell Cycle Interphase consists of

3 stages:

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)

http://www.cellsalive.com/cell_cycle.htm

Cell Cycle Demo

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