Significance and Regulation of Cellular Divisions

"Cancer"

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* A cell must maintain an efficient surface-to-volume ratio

in order to survive, once a cell is of certain size it will

divide.

- chemicals called "growth factors" may then cause the division to occur. (ie. kinetin =

promotes division in plants.

- contact inhibition - may also help control cell division

- cells touch each other.

- to overcome the limits of surface-to-volume ratios, an organism must be multicellular.

- if a cell were to grow too big in size:

- the amount of cytoplasm and number of organelles would increase faster

than the surface area.

- surface area could not keep up with providing nutrients and ridding

wastes.

- cell dies (or stops growing)

* Most cells in an organism have the same DNA.

- however, only certain parts of the DNA are active, thus producing specific

proteins.

* Group of similar cells = tissues

Group of similar tissues = organs

Group of organs working together = system

* Some cells lose the ability to regulate their rate of division and grow into

tumors:

- benign = not necess. life threatening

- cells grow in one area of the body

- can be surgically removed

- however, they can grow, become painful or interfere with an organ's

normal function.

ie.'s - warts (virus enters skin cells causing the skin cells to rapid

replicate).

- skin tags (tiny nobs of raised skin cells)

- breast tumors (most tumors in breast tissue are benign)

Note: - "a mole" is not tumor related

- melanocytes (cells in skin that produce melanin) that are in high

concentration develop from the epidermis->epidermis/dermis->dermis while

growing larger

- note however that ~1/3 of melanomas come from pre-existing moles

- malignant = can be life threatening

- cells of a tumor spread to other tissues (bloodstream helps).

- ie. malignant breast tumors kill 20,000+ women per year.

Cancer - is when malignant cells invade and destroy tissue.

- cells do not necess. grow faster than healthy cells

- they just keep on dividing.

- normal cells divide about 50x, cancers cells go past this limit

- cells absorbs more nutrients than a normal cell.

- cells can secrete a substance that promotes blood vessel production

(neovascularization)

- cells do not stick to each other, so they can break away from the

main cluster

- cells have irregular shapes and sizes and usual number of nucleoli.

- cells divide before they are mature and grow

all over themselves (not effected by contact inhibition)

- ~ 100 different types of cancer

- ~ 1 out of 4 people will die from cancer (~27%=Lung)

- 3 Main types:

Carcinoma = epithelial (skin, large intestine, lungs,

stomach, prostate gland, breast)

ie. Melanoma = melanocytes (skin cells)

Sarcoma = soft tissues (fatty tissue, bone, muscular, vascular)

ie. Osteosarcoma = (bone)

Leukemia = leukocytes (too many immature white blood cells)

- “liquid cancer”

Lymphoma = lymphoid tissue(develop in the glands or nodes of the

lymphatic system)

- “solid cancer”

carcinogens - cancer-causing agent (ie.'s radiation, viruses, and chemicals) all

effect DNA

- ie. radiation --> skin --> ultraviolet --> breaks DNA in skin cells --> if

break disrupts the gene that controls cell division -->

affected cells --> cancerous

- ie. viruses --> inject their own DNA into a cell --> defective DNA does not

respond to normal regulators of cell growth and division

–-> cancerous

- ie. chemicals --> attack base pairs in DNA --> some alteration of base

pairs --> during DNA replication, new base pairs will not

accurately pair with old ones --> if this occurred to

bases that make up a gene that controls cell division -->

cancerous