Life Span of CellsDifferent cells in our bodies have different

life spans.

Some cells, such as skin cells or those lining your digestive system, need to divide more frequently.

Other cells, such as neurons, rarely divide.

The Cell CycleThe cell cycle is divided into two main parts:

InterphaseCell Division (Mitosis and Cytokinesis)

Interphase is sometimes called the “resting phase” but the cells are never resting. They are carrying out the functions required for life (taking in oxygen and nutrients, releasing energy from glucose, removing waste products).

DNA replication also occurs during interphase.

Checkpoints

There are 3 main checkpoints in the cell cycle.Proteins in the cell will stop the cell cycle if

something is wrong.In general, cell division will not occur if:

There is not enough nutrients to support cell growthThe DNA has not replicatedThe DNA is damaged

Cell DeathSome cells die because they have been

damaged by physical forces or by exposure to toxic chemicals.

Some cells die because of “preprogrammed cell death” or “apoptosis”

During apoptosis lysosomes break open and enzymes digest the cell.

Apoptosis is necessary for the development of fingers and toes.

Cancer

Cancer occurs when a cell ignores the checkpoints and divides uncontrollably.

A clump of cells called a tumour is formed.Some tumours are benign and others are

cancerous (malignant).Cancer cells interfere with the function of

normal cells around them. They can also use up nutrients that are needed by the healthy cells.

Comparing normal cells to cancer cells

Watch the video and make a T-chart comparing normal cells and cancer cells.

cancer cells vs. normal cells

The development of cancer

What can be done?From cancer.ca

Live WellDon’t smokeEat healthyStay activeLimit alcoholProtect yourself from UV rays

Be aware: Cancer is most treatable when found earlyKnow your body and

don’t ignore changes.Know your family

medical history.There is a connection

between some viruses and cancer (eg. HPV)

Limit your exposure to cancer-causing substances (carcinogens).

Your TaskP. 45 #1-6

In your opinion, what percentage of research dollars should be spent on the following:Finding causes of cancerFinding new treatments for cancerCancer prevention

Justify your answer in a well-written paragraph