The Key Roles of Cell Division

The Key Roles of Cell Division • Essential for perpetuation of life: Reproduction of unicellular forms • Development, Growth, & Repair of multicellular forms

The Mitotic Cycle • Interphase  90% • G1 = Grow, normal fx. • S = Synthesis of DNA • G2 = Prepares for cell division • Mitosis • PMAT • Cytokinesis –cell pinches in 2

Interphase • Nucleus is well defined in a nuclear envelope • DNA is in the form of loosely packed chromatin fibers • Accounts for 90% of cell cycle

Prophase • Chromosomes become visible • The nucleoli and nuclear envelope begin to disappear • Spindle forms

Metaphase • Chromosomes line up along the Middle

Anaphase • chromosomes move to opposite poles of the cell.

Telophase • Nuclear envelope forms at each pole • Chromosomes uncoil • Cleavage furrow

http://www.cellsalive.com/cell_cycle.htm • http://www.cellsalive.com/mitosis.htm

Conjoined Twins http://www.youtube.com/watch?v=ZzZYKggrB34&feature=fvsr http://www.youtube.com/watch?v=XM82Hs0LEpc

5.4 Cell Cycle Controland Mutation Controls in the Cell Cycle • Checkpoints exist in the cell cycle • Cell determines if cell is ready to enter next part of cell cycle http://highered.mcgraw-hill.com/olc/dl/120082/bio34a.swf

5.1 What Is Cancer? • Cancer begins when the proteins that regulate the cell cycle don’t work, the cell divides uncontrollably • Mutations can be inherited or induced by exposure to U.V. radiation or carcinogens that damage DNA and chromosomes

Cancer: Uncontrolled cell growth • Tumor • Malignant vs benign • Metastasis • Types of cancer • Carcinoma (epithelials) • Melanoma (melanocytes) • Sarcoma (muscle/connective) • Osteogenic (bone) • Leukemia (blood forming organs) ↑ WBC’s • Lymphoma (lymphatic) • Malignant cells trigger angiogenesis

Mutations to Cell-CycleControl Genes • Proto-oncogenes: Normal genes on many different chromosomes regulate cell division • When mutated, they become oncogenes • Many organisms have proto-oncogenes, so many organisms can develop cancer

From Benign to Malignant • Angiogenesis – growth of blood cells caused by secretions from cancer cells • Increases the blood supply to cancer cells: more oxygen and nutrients • Cancer cells can divide more • Tumors develop, sometimes filling entire organs

From Benign to Malignant • Contact inhibition in normal cells prevents them from dividing all the time, which would force the new cells to pile up on each other • Anchorage dependence in normal cells keeps the cells in place

Multiple Hit Model • Many changes, or hits, to the cancer cell are required for malignancy • Mutations can be inherited and/or can stem from environmental exposures • Knowledge of cancer risk factors is important • Earlier detection and treatment of cancer greatly increase the odds of survival

Detection Methods: Biopsy • Different cancers are detected by different methods, including high protein production possibly indicating a tumor • Biopsy, the surgical removal of cells, tissue, or fluid for analysis is performed • Under a microscope, benign tumors appear orderly and resemble other cells in the same tissue • Malignant tumors do not resemble normal tissue

5.6 Meiosis • Occurs within gonads (testes:ovaries) • Meiosis produces sex cells – gametes (sperm:egg) • Gametes have half the chromosomes (23) that somatic cells do (46) • Meiosis reduces the number of chromosomes by one-half

Meiosis contributes to Genetic Variation • There are millions of possible combinations of genes that each parent can produce because of: • Random alignment of homologous pairs • Crossing over • Random Feritlization (70 trillion)

Birth = paused at prophase I Puberty = finishes meiosis I Fertilization = finishes meiosis

*somatic cells *divide once diploid *forms identical cells *gametes *divide twicehaploid *forms different cells (crossing over) http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter12/animations.html#

The Key Roles of Cell Division