Download Cell Cycle

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:

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