Cell Cycle

• A cell is very small with an average size of 1/100th of a millimeter

Cell Cycle

• A human is made of about 10 trillion cells.

• But the number of bacteria cells both on and in one human is more than that!!!

Each fertilized cell DIVIDES and Divides and DIVIDES and DIVIDES .

Development of a Frog Egg

• Early development in a frog egg illustrates how a single egg develops hundreds of cells through division.

Why Are Cells small?

• Cells are small to let materials easily and quickly diffuse into all parts of the cell.

• Which materials diffuse in?

____________________________

• Cells are small to let materials easily and quickly diffuse out of all parts of the cell.

• Which materials diffuse out?

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Glucose and oxygen

Carbon dioxide and wastes

• A cell grows to its optimal size and then it divides in half.

• Each half will form a new cell that grows until it reaches its optimal size, and then it too will divide in half.

Exception

• A bird’s egg is one large cell. The yolk is a food source for the growing embryo.

• How is it possible for a bird’s egg to function when it is so large?

Food is already present—diffusion isn’t needed to meet the nutritional needs of cell

• 1 parent cell divides into 2 daughter cells.

• When the cell divides in half, the DNA (genetic material) and cytoplasm must be divided evenly

• A structure found in the nucleus of cells

• Each chromosome is one molecule of DNA wrapped around proteins

Chromosomes

Proteins

DNA

Cells and Chromosomes

• Each cell contains a nucleus with chromosomes.

• Each species has a characteristic number of chromosomes.

• Humans have 46 chromosomes in the nucleus of each of their cells (23 chromosomes from each parent)

The Cell Cycle

• Interphase: Longest part of cell cycle (90%). This is when the cell is “doing its job”. – Cell grows; proteins and organelles are made– At the end of Interphase the cell gets ready

to divide by copying each of the chromosomes

Interphase Start of Cell Division

Cell Division

• Mitosis (4 phases) = division of the cell’s nucleus

What happens?– Chromosomes can

be seen in the nucleus (they look like dark spaghetti)

– Each chromosome is made up of two identical copies, attached together in the middle.

• Spindles - Fan-like structures grow out from the opposite ends of the cell

• The nucleolus disappears.

• The nuclear envelope breaks down*.

 

Centrioles

Sister Chromatids

Chromosome

DNA

Interphase Mitosis

Cell Division

• Chromosomes line up at the center of the cell.

• Each chromosome is attached to a spindle fiber at the center.

• Anaphase– Spindles shorten --

causing the chromosomes to move towards opposite ends of the cell near the poles of the spindles*.

• Telophase– Chromosomes

gather at either end of the cell and begin to lose their shape.

– A nuclear envelope forms around each group of chromosomes.

– Spindle fibers break apart.  

• Division of cytoplasm

• Occurs at same time as telophase

• Cell membrane pinched into two parts with one nucleus and an equal number of organelles in each part.

• New cell membrane forms around each cell*.

 

• The Whole Process*

The Purpose of Cell Division

• Multicellular organisms = growth, development and repair

What Happens when there are Problems with the Cell Cycle?

• Cancer is a family of diseases. Some are relatively easy to cure, others are fatal. – All types of cancer involve a break-down in

the normal cell cycle. – All cancer cells divide at a rapid rate

indefinitely without stopping.

• Usually, a cell that does not respond to the cell cycle controls is destroyed.

• If not, a tumor forms = a mass of abnormal cells developing within a tissue.

• Cells are disorganized and grow irregularly.

• Benign tumors - remain at original site, are non-invasive and can be surgically removed. They do not spread to other parts of the body.

• Malignant tumors - cause cancer--cells invade and disrupt functioning of organs. These cells usually contain an abnormal number of chromosomes.

Types of tumors (continued)

• Metastases - Cancer cells (depending on type) may be invasive. Cells from a tumor may break off and spread through the body in blood cells and invade other organs*.

Types of Cancers

• Leading cancers in the USA– Bladder Cancer – Lung Cancer– Breast Cancer – Melanoma– Colon and Rectal Can

cer 

– Non-Hodgkin Lymphoma

– Endometrial Cancer – Pancreatic Cancer– Kidney (Renal Cell)

Cancer – Prostate Cancer– Leukemia – Thyroid Cancer

• In USA: 1 of 4 deaths is caused by cancer.

• What causes cancer cells to form? – Smoking tobacco– Exposure to radiation– Certain viruses– Environmental factors – Genetic factors

• First step (usually) is surgical removal of tumor.

• If all cancer cells are removed and the affected organ is not damaged the person is considered cured.

• Other treatments: – Radiation therapy– Chemotherapy

 

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