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% –G 1 = Grow, normal fx. –S = Synthesis of DNA –G 2 = 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

om/cell_cycle.htmhttp:// om/cell_cycle.htm om/mitosis.htmhttp:// om/mitosis.htm

Conjoined Twins grB34&feature=fvsr 0LEpc

5.4 Cell Cycle Control and 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 hill.com/olc/dl/120082/bio 34a.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-Cycle Control 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) mcgraw- hill.com/sites/ /stu dent_view0/ch apter12/animat ions.html#