Cell Growth & Division Biology  Pearland ISD

Cell Division There are 2 main reasons cell divides: The cell has more trouble trying to move nutrients and wastes across the cell membrane. The larger a cell becomes, the greater the demand it puts on its DNA. Bottom line – cells need to be replaced

Cell Cycle The sequence of growth and division of a cell An average cycle may be 22 hours Three general periods: resting phase growth phase division phase

G0 (Resting phase) Non-dividing, differentiated state. Most human cells are in G0 phase. Liver cells: Generally in G0, but can be “called back” to cell cycle by external cues. Nerve & muscle cells: Highly specialized. Arrested in G0 & can never divide.

Interphase (Growth phase) Most of the cell’s life is spent in interphase Longest phase –(90% of cell’s growth) Centrioles – help to organize cell division Chromatin – DNA bound protein within the nucleus

Interphase (Growth phase) New DNA is formed during 3 phases: G1 – 1st period of growth 1. Increase in size. 2. Makes new proteins and organelles. S – DNA is synthesized or replicated 1. Chromosomes are replicated. 2. New DNA molecules are made. G2 – final cell growth 1. Shortest phase 2. Prepares cell for mitosis

Terms to know Chromosome – contains genetic information (DNA) passed from one generation to the next Spindle – microtubule that helps separate chromosomes A – centromere: center of chromosome B – chromatids: two identical “sister” parts of the chromosome

Takes place within the nucleus of the cell. Mitosis Takes place within the nucleus of the cell.

Mitosis (Division phase) 4 Phases: (PMAT) Prophase Metaphase Anaphase Telophase

4 phases that blend from one to another

Prophase 1st and longest phase of mitosis Chromatin become chromosomes Chromatids are joined by centromere Nucleus disappears Centrioles migrate to poles Spindles are formed

Metaphase 2nd phase of mitosis Chromosomes meet in the middle of cell Pulled by spindles Each chromosome is attached to top of spindle

Anaphase 3rd phase of mitosis Centromeres are split apart Chromatids are pulled apart and begin to drift to opposite poles

Telophase Final phase of mitosis Begins when chromatids reach poles New nucleus starts to form Chromosomes start to unwind Spindles disappear Cytoplasm begins to divide

Cytokinesis Cytoplasm pinches in half Each daughter cell has an identical set of chromosomes

http://www.youtube.com/watch?v=JcZQkmooyPk&feature=player_embedded

Cancer Cancer is a disorder where the cell has uncontrolled growth. Cancer cells do NOT respond to regulators. This causes the cells to form masses called tumors, which can damage surrounding tissues.

Cancer Development Cancer develops only after a cell experiences ~6 key mutations (“hits”). Unlimited growth Turn ON growth promoter genes. Ignore checkpoints Turn OFF tumor suppressor genes. Escape apoptosis Turn OFF suicide genes. Immortality = unlimited divisions Turn ON chromosome maintenance genes. Promotes blood vessel growth Turn ON blood vessel growth genes. Overcome anchor & density dependence Turn OFF touch-sensor gene.

Cancer Triggers Mutations in cells can be triggered by: UV radiation Chemical exposure Radiation exposure Heat Cigarette smoke Pollution Age Genetics

Growing out of control, cancer cells produce malignant tumors Cancer cells do not respond normally to the cell cycle control system Divide excessively. Can invade other tissues. May kill the organism.

If an abnormal cell avoids destruction by the immune system, it may form a tumor Benign: abnormal cells remain at original site Malignant: abnormal cells can spread to other tissues and parts of the body Metastasis: spread of cancer cells through the circulatory system

Cancers are named according to location of origin: Carcinoma: external or internal body coverings Sarcoma: tissues that support the body Leukemia and lymphoma: blood-forming tissues Radiation and chemotherapy are effective as cancer treatments because they interfere with cell division