Copyright Pearson Prentice Hall 10-2 Cell Division Photo Credit: © CAMR/A.B. Dowsett/Science Photo Library/Photo Researchers, Inc. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Cell Division In eukaryotes, cell division occurs in two major stages. The first stage, division of the cell nucleus, is called mitosis. The second stage, division of the cell cytoplasm, is called cytokinesis. Copyright Pearson Prentice Hall

Chromosomes Chromosomes Genetic information is passed from one generation to the next on chromosomes. Before cell division, each chromosome is duplicated, or copied.

Copyright Pearson Prentice Hall Chromosomes Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Chromosomes Each chromosome consists of two identical “sister” chromatids. Each pair of chromatids is attached at an area called the centromere. Sister chromatids Photo Credit: © Gunther F. Bahr/AFIP/Stone Centromere Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Chromosomes When the cell divides, the chromatids separate. Each new cell gets one chromatid. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Cell Cycle Cell Cycle The cell cycle is the series of events that cells go through as they grow and divide. Interphase is the period of growth that occurs between cell divisions. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Cell Cycle During the cell cycle: a cell grows prepares for division divides to form two daughter cells, each of which begins the cycle again Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The cell cycle consists of four phases: G1 (First Gap Phase) S Phase G2 (Second Gap Phase) M Phase Copyright Pearson Prentice Hall

Events of the Cell Cycle During G1, the cell increases in size synthesizes new proteins and organelles Copyright Pearson Prentice Hall

Events of the Cell Cycle During the S phase, chromosomes are replicated DNA synthesis takes place Once a cell enters the S phase, it usually completes the rest of the cell cycle. Copyright Pearson Prentice Hall

Events of the Cell Cycle The G2 Phase (Second Gap Phase) organelles and molecules required for cell division are produced Once G2 is complete, the cell is ready to start the M phase—Mitosis Copyright Pearson Prentice Hall

Events of the Cell Cycle During the cell cycle, the cell grows, replicates its DNA, and divides into two daughter cells. DNA synthesis takes place during the S phase. Cell division takes place during the M phase. G1 and G2 are gap phases. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Mitosis Mitosis Biologists divide the events of mitosis into four phases: (PMAT) Prophase Metaphase Anaphase Telophase Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Mitosis Most eukaryotic cells go through a regular cycle of interphase, mitosis and cytokinesis. Mitosis has four phases: Prophase, Metaphase, Anaphase and Telophase. The events shown here are typical of animal cells. Mitosis Copyright Pearson Prentice Hall

Chromosomes (paired chromatids) Mitosis Section 10-2 Spindle forming Prophase Prophase Chromosomes (paired chromatids) Centromere Most eukaryotic cells go through a regular cycle of interphase, mitosis and cytokinesis. Mitosis has four phases: Prophase, Metaphase, Anaphase and Telophase. The events shown here are typical of animal cells. Click to Continue Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Mitosis Spindle forming Prophase Prophase is the first and longest phase of mitosis. The centrioles separate and take up positions on opposite sides of the nucleus. Centromere Chromosomes (paired chromatids) Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Mitosis Spindle forming The centrioles lie in a region called the centrosome. The centrosome helps to organize the spindle, a fanlike microtubule structure that helps separate the chromosomes. Centromere Chromosomes (paired chromatids) Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Mitosis Spindle forming Chromatin condenses into chromosomes. The centrioles separate and a spindle begins to form. The nuclear envelope breaks down. Centromere Chromosomes (paired chromatids) Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Mitosis Metaphase Centriole Spindle Centriole Metaphase Click to Continue Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Mitosis Centriole Metaphase The second phase of mitosis is metaphase. The chromosomes line up across the center of the cell. Microtubules connect the centromere of each chromosome to the poles of the spindle. Spindle Copyright Pearson Prentice Hall

Individual chromosomes Mitosis Anaphase Individual chromosomes Anaphase Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Mitosis Anaphase Anaphase is the third phase of mitosis. The sister chromatids separate into individual chromosomes. The chromosomes continue to move until they have separated into two groups. Individual chromosomes Copyright Pearson Prentice Hall

Nuclear envelope reforming Mitosis Telophase Nuclear envelope reforming Telophase Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Mitosis Telophase Telophase is the fourth and final phase of mitosis. Chromosomes gather at opposite ends of the cell and lose their distinct shape. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Mitosis A new nuclear envelope forms around each cluster of chromosomes. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Cytokinesis Cytokinesis Cytokinesis Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Cytokinesis During cytokinesis, the cytoplasm pinches in half. Each daughter cell has an identical set of duplicate chromosomes Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Cytokinesis in Plants In plants, a structure known as the cell plate forms midway between the divided nuclei. Cell plate Cell wall Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The series of events that cells go through as they grow and divide is called the cell cycle. mitosis. interphase. cytokinesis. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The phase of mitosis during which the chromosomes line up across the center of the cell is prophase. metaphase. anaphase. telophase. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Cytokinesis usually occurs at the same time as telophase. after telophase. during interphase. during anaphase Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall DNA replication takes place during the S phase of the cell cycle. G1 phase of the cell cycle. G2 phase of the cell cycle. M phase of the cell cycle. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall During mitosis, “sister” chromatids separate from one another during telophase. interphase. anaphase. metaphase. Copyright Pearson Prentice Hall

10-3 Regulating the Cell Cycle Copyright Pearson Prentice Hall

Controls on Cell Division Experiments show that normal cells will reproduce until they come into contact with other cells. When cells come into contact with other cells, they respond by not growing. This demonstrates that controls on cell growth and division can be turned on and off. Copyright Pearson Prentice Hall

Controls on Cell Division Contact Inhibition Cells in a petri dish will continue to grow until they come into contact with other cells. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Cell Cycle Regulators How is the cell cycle regulated? Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Cell Cycle Regulators Cell Cycle Regulators The cell cycle is regulated by a specific protein. The amount of this protein in the cell rises and falls in time with the cell cycle. Scientists called this protein cyclin because it seemed to regulate the cell cycle. Cyclins regulate the timing of the cell cycle in eukaryotic cells. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Cell Cycle Regulators Cyclins were discovered during a similar experiment to this one. The timing of the cell cycle is regulated by cyclins. When cytoplasm from a cell in mitosis is injected into another cell, the second cell enters into mitosis. The reason for this effect is a protein called cyclin, which triggers cell division. A sample of cytoplasm is removed from a cell in mitosis. The sample is injected into a second cell in G2 of interphase. As result, the second cell enters mitosis. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Cell Cycle Regulators Internal Regulators  Internal regulators allow the cell cycle to proceed only when certain processes have happened inside the cell. Example: p53 Gene that regulates the passage into mitosis Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Cell Cycle Regulators External Regulators  Proteins that respond to events outside the cell are called external regulators. External regulators direct cells to speed up or slow down the cell cycle. Copyright Pearson Prentice Hall

Uncontrolled Cell Growth Cancer is a disorder in which some of the body's own cells lose the ability to control growth. How are cancer cells different from other cells? Copyright Pearson Prentice Hall

Uncontrolled Cell Growth Cancer cells do not respond to the signals that regulate the growth of most cells. Copyright Pearson Prentice Hall

Uncontrolled Cell Growth Cancer cells divide uncontrollably and form masses of cells called tumors that can damage the surrounding tissues. Cancer cells may break loose from tumors and spread throughout the body, disrupting normal activities and causing serious medical problems or even death. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The cell cycle is believed to be controlled by proteins called spindles. cyclins. regulators. centrosomes. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Proteins that respond to events inside the cell are called internal regulators. external regulators. cyclins. growth factors. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 10-3 Once a multicellular organism reaches adult size, the cells in its body stop dividing. grow and divide at different rates, depending on the type. have the same life span between cell divisions. undergo cell division randomly. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 10-3 One effect of an internal regulator is that a cell will not begin mitosis until it becomes too large. the cell’s growth is stimulated. it is in physical contact with other cells. all its chromosomes have been replicated. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall One factor common to almost all cancer cells is a lack of cyclin. a defect in gene p53. exposure to tobacco smoke. exposure to radiation. Copyright Pearson Prentice Hall