Cell Growth and Division Chapter 10 Cell Growth and Division

10–1 Cell Growth Photo Credit: © CAMR/A.B. Dowsett/Science Photo Library/Photo Researchers, Inc.

10–1 Cell Growth Limits to Cell Growth The larger a cell becomes, the more demands the cell places on its DNA. In addition, the cell has more trouble moving enough nutrients and wastes across the cell membrane.

10–1 Cell Growth The rate at which food, oxygen, water, and wastes are moved in and out of the cell is dependent on the surface area of the cell. The rate at which food, oxygen and water are used and waste is produced depends on the cell’s volume.

Limits to Cell Growth Ratio of Surface Area to Volume As the length of a cell increases, its volume increases faster than the surface area. The decrease in the cell’s ratio of surface area to volume makes it more difficult for the cell to move needed materials in and waste products out quickly enough for the cell to survive.

Limits to Cell Growth As the length of a cell increases, its volume increases faster than its surface area. The resulting decrease in the cell’s ratio of surface area to volume makes it more difficult for the cell to move needed materials in and waste products out.

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

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.

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

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

Chromosomes When the cell divides, the chromatids separate. Each new cell gets one chromatid. Each “sister” is identical

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.

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

The Cell Cycle The cell cycle consists of four phases: G1 (First Gap Phase) Growth S Phase G2 (Second Gap Phase) Growth M Phase

Events of the Cell Cycle During G1, the cell increases in size Growth synthesizes new proteins and organelles

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.

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

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.

Mitosis Mitosis four phases: Prophase Metaphase Anaphase Telophase

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

Chromosomes (paired chromatids) Mitosis Section 10-2 Prophase Prophase Spindle forming 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

Mitosis Prophase Prophase is the first and longest phase of 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. The nuclear envelope breaks down Chromosomes coil up Centromere Chromosomes (paired chromatids)

Mitosis Metaphase Metaphase Click to Continue Centriole Spindle

Mitosis Centriole 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

Individual chromosomes Mitosis Anaphase Individual chromosomes Anaphase

Mitosis Individual chromosomes Anaphase The sister chromatids separate into individual chromosomes. The chromosomes continue to move until they have separated into two groups.

Nuclear envelope reforming Mitosis Telophase Nuclear envelope reforming Telophase

Mitosis Telophase Chromosomes gather at opposite ends of the cell and lose their distinct shape. A new nuclear envelope forms around each cluster of chromosomes.

Cytokinesis Cytokinesis Cytokinesis

Cytokinesis During cytokinesis, the cytoplasm pinches in half. Chromosomes uncoil Each daughter cell has an identical set of duplicate chromosomes

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

Cytokinesis in Plants The cell plate gradually develops into a separating membrane. A cell wall then begins to appear in the cell plate.

11-4 Meiosis 11-4 Meiosis

Each organism must inherit a single copy of every gene from each of its “parents.” Gametes are formed by a process that separates the two sets of genes so that each gamete ends up with just one set.

Chromosome Number Chromosome Number Different types of organisms have different numbers of chromosomes. These chromosomes are from a fruit fly. Each of the fruit fly’s body cells has 8 chromosomes.

Chromosome Number These two sets of chromosomes are homologous. Each of the chromosomes that came from the male parent has a corresponding chromosome from the female parent.

Chromosome Number A cell that contains both sets of homologous chromosomes is said to be diploid. represented by the symbol 2N.

Chromosome Number The gametes of sexually reproducing organisms contain only a single set of chromosomes, and therefore only a single set of genes. These cells are haploid. Haploid cells are represented by the symbol N.

Phases of Meiosis Phases of Meiosis Meiosis is a process of reduction division in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell.

Phases of Meiosis Meiosis involves two divisions, meiosis I and meiosis II. By the end of meiosis II, the diploid cell that entered meiosis has become 4 haploid cells.

Telophase I and Cytokinesis Phases of Meiosis Meiosis I Meiosis I Interphase I During meiosis, the number of chromosomes per cell is cut in half through the separation of the homologous chromosomes. The result of meiosis is 4 haploid cells that are genetically different from one another and from the original cell. Prophase I Metaphase I Anaphase I Telophase I and Cytokinesis

Phases of Meiosis Interphase I Cells undergo a round of DNA replication, forming duplicate chromosomes. Interphase I - Cells undergo a round of DNA replication, forming duplicate chromosomes.

Phases of Meiosis MEIOSIS I Prophase I Each chromosome pairs with its corresponding homologous chromosome to form a tetrad. MEIOSIS I Prophase I - Each chromosome pairs with its corresponding homologous chromosome to form a tetrad.

Phases of Meiosis When homologous chromosomes form tetrads in meiosis I, they exchange portions of their chromatids in a process called crossing over. Crossing-over produces new combinations of alleles. Crossing-over occurs during meiosis. (1) Homologous chromosomes form a tetrad. (2) Chromatids cross over one another. (3) The crossed sections of the chromatids are exchanged.

Phases of Meiosis Meiosis II The two cells produced by meiosis I now enter a second meiotic division. Unlike meiosis I, neither cell goes through chromosome replication. Each of the cell’s chromosomes has 2 chromatids.

Telophase II and Cytokinesis Phases of Meiosis Meiosis II During meiosis, the number of chromosomes per cell is cut in half through the separation of the homologous chromosomes. The result of meiosis is 4 haploid cells that are genetically different from one another and from the original cell. Meiosis II Telophase I and Cytokinesis I Metaphase II Anaphase II Telophase II and Cytokinesis Prophase II

Phases of Meiosis Meiosis II results in four haploid (N) daughter cells, each with half the number of chromosomes as the original cell. MEIOSIS II Prophase II - Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original cell.

Gamete Formation Gamete Formation In male animals, meiosis results in four equal-sized gametes called sperm. Meiosis produces four genetically different haploid cells. In males, meiosis results in four equal-sized gametes called sperm.

Gamete Formation In many female animals, only one egg results from meiosis. The other three cells, called polar bodies, are usually not involved in reproduction. Meiosis produces four genetically different haploid cells. In females, only one large egg cell results from meiosis. The other three cells, called polar bodies, usually are not involved in reproduction.

10-3 Regulating the Cell Cycle

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.

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

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.

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.

Cell Cycle Regulators Internal Regulators  Proteins that respond to events inside the cell are called internal regulators. Internal regulators allow the cell cycle to proceed only when certain processes have happened inside the cell.

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.

Uncontrolled Cell Growth Cancer is a disorder in which some of the body's own cells lose the ability to control growth. Cancer cells do not respond to the signals that regulate the growth of most cells.

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.