Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies How Cells Divide Chapter 6 Copyright © McGraw-Hill Companies Permission required for reproduction or display

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Outline Simple Cell Cycle Complex Cell Cycle Chromosomes Mitosis  Cancer Meiosis I Meiosis II Evolutionary Consequences of Sex

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Simple Cell Cycle Cell division in bacteria takes place in two stages (Simple Cell Cycle).  DNA is copied  Cell Splits (Binary Fission) - Forms two daughter cells Heredity information in bacteria encoded in single circle of DNA. Copyright © McGraw-Hill Companies Permission required for reproduction or display

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Complex Cell Cycle Eukaryotic DNA is contained in linear chromosomes.  Long DNA molecules packaged with proteins. Mitosis - Mechanism of cell division occurring in non-reproductive (somatic) cells. Meiosis - Mechanism of cell division occurring in reproductive (germ) cells.

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Complex Cell Cycle G 1 phase - Primary growth phase S phase - DNA replicates G 2 phase - Microtubule synthesis M phase - Chromosomes pull apart C phase - Cytokinesis

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Complex Cell Cycle Copyright © McGraw-Hill Companies Permission required for reproduction or display

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Chromosomes Human cells each have 23 nearly identical pairs of chromosomes, for a total of 46.  Each chromosome contains thousands of genes that play important roles in body development and function. Copyright © McGraw-Hill Companies Permission required for reproduction or display

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Chromosome Structure DNA helix is wrapped around proteins with positive charges (histones) and negative charges counteracting each other.

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Chromosome Structure Homologues - Nearly identical copies of the same chromosomes. Diploid Cells - Two copies of chromosomes.  Before cell division, each homologue replicates, resulting in two identical copies (sister chromatids). - Remain attached at centromere. Copyright © McGraw-Hill Companies Permission required for reproduction or display

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Cell Division Interphase - Chromosomes replicate and begin to wind up tightly. Mitosis  Prophase - Nuclear envelope breaks down, DNA further condenses, and spindle fibers form.  Metaphase - Chromosomes align at center of cell and kinetochore fibers attach to centromeres.

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Copyright © McGraw-Hill Companies Permission required for reproduction or display

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Mitosis  Anaphase - Centromeres replicate and sister chromatids separate and move towards opposite poles.  Telophase - Nuclear envelope reappears and chromosomes decondense.

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Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Cytokinesis Cytokinesis - Division of cytoplasm.  Animal cells - Cell pinches in two with contracting belt of microtubules, forming a cleavage furrow.  Plant cells - Membrane assembled at right angle to mitotic spindle. Cell plate grows outward until it reaches the interior surface of plasma membrane.

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies

Controlling Cell Cycle At critical points, further cell progress depends on a central set of switches regulated by cell feedback.  G1 – Cell growth assessed  G2 DNA replication assessed  M mitosis assessed

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Cancer Cancer - Unrestrained cell growth and division.  Tumor - Cluster of cells. - Benign - Encapsulated and noninvasive. - Malignant - Not encapsulated, invasive, and shed cells.  Metastases - Process of cells shedding from a malignant tumor and spreading to distant parts of the body.

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Cell Cycle Control Gene p53 plays a key role in G 1 checkpoint of cell division.  Gene’s product monitors integrity of DNA, checking for successful replication. - If protein detects damaged DNA, it halts cell division and stimulates repair enzymes.  Nonfunctional p53 genes allow cancer cells to repeatedly divide.

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Curing Cancer Preventing cancer from starting by focusing on decision-making process to divide.  Receiving the signal to divide  Relay switch  Amplifying the signal  Releasing the brake  Checking that everything is ready  Stepping on the gas

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Curing Cancer Preventing the Spread of Cancer  Tumor growth - Angiogenesis inhibition  Metastasis

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Molecular Cancer Therapies

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Meiosis Gamete formation must involve some mechanism to halve the number of chromosomes.  Two sets of chromosomes are present in somatic cells of adults (diploid), but only one set is present in gametes (haploid). - Sexual Reproduction involves the alteration of meiosis and fertilization.

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Alteration of Generations Copyright © McGraw-Hill Companies Permission required for reproduction or display

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Stages of Meiosis Meiosis I  Prophase I - Chromosomes pair up and exchange segments (Crossing Over).  Metaphase I - Chromosomes align at cell’s center (Independent Assortment).  Anaphase I - Homologous pairs pulled apart.  Telophase I - Individual chromosomes gather at each of the poles.

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Crossing Over

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Meiosis II Mitotic division involving products of Meiosis I.  Prophase II - Nuclear envelope breaks down and spindle fibers form.  Metaphase II - Spindle fibers bind to both sides of centromeres.  Anaphase II - Spindle fibers contract, moving sister chromatids to opposite poles.  Telophase II - Nuclear envelope reforms around four sets of daughter cells.

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Evolutionary Consequences of Sex Genetic Diversity  Independent Assortment  Crossing Over  Random Fertilization Copyright © McGraw-Hill Companies Permission required for reproduction or display

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Review Simple Cell Cycle Complex Cell Cycle Chromosomes Mitosis  Cancer Meiosis I Meiosis II Evolutionary Consequences of Sex

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