Mitosis Cell Division Why Cell Division is Important

Mitosis Cell Division

Why Cell Division is Important: • Dead and damaged cells must be replaced. • Every second million of cells are injured in your body. Your cells must reproduce to replace the old ones • Cells must divide or reproduce.

• Cells do not simply get bigger. • It is important that essential materials be able to enter and leave the cell easily through the membrane. • As the cell grows bigger, the distance between the cell membrane and the nucleus gets larger. • The distance to and from the nucleus must be kept short.

The Cell Cycle

• http: //www. youtube. com/watch? v=vw 1 q. Gt. VR 5 l I&feature=related

INTERPHASE • The resting stage of the cell. • The cell grows. • Just before mitosis, nucleus prepares itself for division by making copies of its chromosomes. • Chromosomes thicken. • Centrioles move to opposite ends of the cell.

PROPHASE • Nuclear membrane disappears. • Chromosomes pair up. • Spindle fibres are formed from centrioles (centrosomes in plants; centrosomes also give rise to centrioles in animals)

METAPHASE • Chromosomes are attached to spindle fibres • Chromosomes pair up and line up at the equator of the cell.

ANAPHASE • Fibres shorten and pull the chromosomes towards the centrioles.

TELOPHASE • Nucleus reforms (1 in each new cell). • Spindle fibres disappear. • Cell prepares for division

CYTOKINESIS • “Cell Motion”. • Cytoplasm divides. • 2 daughter cells form. They contain identical genetic information as mother cell.

anaphase prophase telophase metaphase interphase

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The Cell Cycle Type of Body Cell Average Life Span Brain 30 -50 years Red Blood 120 days Stomach lining 2 days Liver 200 days Intestine lining 3 days Skin 20 days • Some types of cells must be “encouraged” to divide, while others must be “encouraged” to remain as they are. • Proteins and other molecules carry signals about cells’ health and abundance to control the cell cycle

Cell Cycle – 2 Stages Cytokinesis A B A – Cell Division B – Interphase: • Cells do whatever activities they are designed to do. • Ex. A muscle cell might produce proteins for muscle contraction. • The cell uses oxygen and glucose, releases energy and removes waste. • DNA replicates in prep for cell division.

Checkpoints • Timing and rate of cell division is controlled and monitored • Specialized proteins act like stop signs • STOP!: 1) There are not enough nutrients to support cell growth 2) The DNA has not replicated 3) The DNA is damaged

Cell Cycle – 2 Stages Cytokinesis A B A – Cell Division B – Interphase Cells are destroyed or repaired!

Cell Death • When cells become old or damaged (by physical forces or exposure to toxic chemicals), they leave the Cell Cycle • Contents leak out, irritating surrounding cells

Cell Suicide • Pre-programmed cell death • Contents of cells are saved, packaged and redistributed so other cells can use them Specialized protein

Cancer • Cancer: Cells with abnormal genetic material that are dividing uncontrollably and can spread to other body parts • Start out normal, transformed, ignore stop signs and divide excessively to form a tumour (abnormal clump of cells) further mutations can become cancer • Bad because it fills up the space that should be filled with normal cells performing normal functions (and use nutrients!)

Cancer continued • Many types of mutations. Ex. Ignore programmed suicide, telomerase (enzyme which signals cells don’t have to stop dividing), division even when not attached to a surface (can lead to spread) • Causes: Chance, inherited, contact with mutagens/carcinogens (e. g. asbestos, tobacco smoke, HPV)