CELL DIVISION

NUCLEUS

•Contains genetic information (DNA)

•Normally, DNA is in the formed of long strands called chromatin.

• During cell division, chromatin winds around proteins making more visible structures called chromosomes.

WHY DIVIDE?

•Multicellular organisms:–To repair or heal–To grow and develop–To replace cells that die

•Unicellular organisms:–To reproduce

Process of Cell Division What happens in each stage of cell

division???

INTERPHASE (STAGE 1)•Cells spend most of their life in interphase.

•Normal cell activities occur.

•Chromosomes are not clearly visible.

•The chromatin looks like spaghetti.

PROPHASE (STAGE 2)•Chromatin condenses and becomes visible as chromosomes.

•The nucleolus disintegrates.

•The nuclear membrane disintegrates.

•Centrioles separate and move to opposite ends (poles) of the cell.

•Spindle fibers are made by the centrioles.

•Each copy of the chromosome is called a chromatid.

•The two chromatids are attached at the centromere.

Chromosome

centromerechromatids

METAPHASE (STAGE 3)•The chromosomes line up at the middle of the cell (equator).

ANAPHASE (STAGE 4)•The joined chromatids separate and move to opposite ends of the cell.

•The chromatids move along the spindle fiber.

•In plant cells, the cell plate begins to form.

TELOPHASE (STAGE 5)•The chromatids arrive at the opposite poles of the cell.

•Spindle fibers disintegrate.

•New nuclear membranes form around the 2 new nuclei.

•Two new nucleoli form

•Individual chromosomes unravel and become chromatin again.

•Cytokinesis or the partitioning of the cell occurs (formation of cleavage).

END RESULTS OF MITOSIS

•Two new “daughter” cells are made with each containing the same number and kinds of chromosomes as the original (parent) cell.

•They have the same genetic code.

CANCER• Caused by uncontrollable cell division.• Cells either fail to stop dividing or get

signals to continue dividing.• An increased number of cells makes a

tumor.• Tumors can be benign (non-cancerous) or

malignant (cancerous).• Cancer cells spread (metastasis)

throughout body!• Chemotherapy (anti-cancer drugs) kills

cancer cells, but unfortunately it also damages healthy cells. This is why people get sick when they undergo chemotherapy.

Some Causes of Cancer•Genetics•Radiation•Carcinogens•Age•Viruses and Bacteria•Diet