1. The Cell Cycle

2. The Cell Cycle
We know cells undergo mitosis to divide… but what are they doing the rest of the time?
The Cell Cycle is the series of events that cells go through as they grow and divide
During the Cell Cycle, a cell:
Grows
Prepares for division
Divides into two daughter cells (each of which then begins the cycle again)

3. Events of the Cell Cycle
Interphase is the longest part of the Cell Cycle, while division takes place quickly
Interphase is divided into three phases
After G2, the cell enters M phase (which is when mitosis happens)
Cell Cycle Phase (all Interphase)
Description of Phase G1
Cell growth S
DNA replication G2
Preparation for mitosis

4. Regulating the Cell Cycle
In a multicellular organism such as us, cell growth and division are controlled very carefully
Not all cells move through the cell cycle at the same rate
For example, most of our muscle cells & nerve cells do not divide at all once they have developed
While the cells of our skin, digestive tract & blood grow and divide rapidly throughout life

5. Regulating the Cell Cycle
In such cells that grow and divide rapidly, they may pass through a complete cycle every few hours
This process provides new cells to replace those that wear out or break down
Controls on cell growth and cell division can actually be turned on and off by the cells

6. Regulating the Cell Cycle
The same thing happens in our body
When an injury such as a cut in the skin or a break in a bone occurs, cells at the edges of the injury are stimulated to divide rapidly
This action produces new cells, starting the process of healing
When the healing process nears completion, the rate of cell division slows down, controls on growth are restored, and everything returns to normal

7. Uncontrolled Cell Growth
Why is cell growth regulated so carefully?
The main reason may be that the consequences of uncontrolled cell growth in a multicellular organism are very severe
For example, cancer is a disorder in which some of the body’s own cells lose the ability to control growth

8. Uncontrolled Cell Growth
Cancer cells do not respond to the signals that regulate the growth of most cells
As a result, they divide uncontrollably and form masses of cells (called tumors) that can damage the surrounding tissues
Cancer cells may break loose from tumors and spread throughout the body, disrupting normal activities and causing serious medical problems or even death

9. Uncontrolled Cell Growth
Tumors can either be benign or malignant
Benign: the cancer cells stay clumped & the tumor can be removed
Malignant: the tumor can metastasize (or break away) and cause other tumors elsewhere
What causes this loss of control over growth?
It could be environmental (radiation exposure), poor choices (smoking), or genetic predisposition
All cancers have one thing in common: the control over the cell cycle has broken down