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Cell Growth & Division Chapter 10 & 11.4
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Vocabulary cytokinesis homologous diploid haploid meiosis tetrad
crossing-over gamete cyclin cancer stem cell cell division chromatid centromere interphase cell cycle mitosis prophase centriole spindle Metaphase anaphase telophase
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I. Limits to Cell Growth Not enough DNA
As a cell increases in size it doesn’t make more DNA If a cell grows too large, new organelles can’t get the instructions they need to function
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Exchanging Materials: a cell must move nutrients and wastes across the cell membrane
Materials go in and out depending on surface area Food & oxygen is used up depending on volume Ratio of Surface Area to Volume to make it easier, think of the cell as a cube Surface area = length x width x # of sides Ex: 1cm x 1cm x 6 sides = Volume = length x width x height Ex: 1cm x 1cm x 1cm = Double the cell length, what happens? 24/8 or ratio of 3:1 Triple the cell length, what happens? 54/27 or ratio of 2:1 As a cell gets larger, volume increases much more rapidly than surface area. If a cell becomes too big, it cannot exchange materials across the membrane fast enough.
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Cell Size Surface Area (length x width x 6) Volume
(length x width x height) Ratio of Surface Area to Volume
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II. Cell Division Draw Chromosomes
Carries the genetic information from one generation to the next Made up of DNA and proteins Replicated prior to cell division forming two identical “sister” chromatids Chromatids are attached by the centromere Draw sister
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Cell Cycle cell cycle = series of events a cell goes through as it grows and divides A cell grows, prepares for division, and divides to form two daughter cells, each of which begins the cycle again Organized into phases: M phase – cell division mitosis – nucleus division cytokinesis – cytoplasm division Interphase G1 phase – cell growth, makes new organelles S phase – DNA replication G2 phase – preparation for mitosis, more growth, makes more enzymes a cell spends ~90% of its time in interphase
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G1 phase M phase S phase DRAW Fig. 10-4, pg. 245 G2 phase
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DRAW 10-5, pg. 246 Interphase Prophase Cytokinesis Metaphase Anaphase
Spindle forming Prophase Centrioles Centromere Nuclear envelope Chromatin Centriole Chromosomes (paired chromatids) Cytokinesis Spindle Centriole Individual chromosomes Metaphase Nuclear envelope reforming Anaphase Telophase
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Mitosis Prophase Metaphase chromatin condenses centrioles separate
spindle forms (microtubules that help separate chromosomes) Nucleolus disappears, nuclear membrane breaks down Metaphase chromosomes line up across the center of the cell on spindle
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Anaphase sister chromatids separate at centromeres and move apart Telophase chromosomes gather at opposite ends, new nuclear envelopes form
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Cytokinesis To complete the M phase, we must have cytokinesis = division of the cytoplasm of the cell Animal cells - cell membrane is drawn inward until the cytoplasm is pinched into 2 new cells Plant cells - cell plate forms midway between the divided nuclei; the cell plate gradually develops into a separating membrane
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E. Cell Cycle Graphic Organizer
includes M phase Interphase is divided into Mitosis Cytokinesis is divided into G1 phase S phase G2 phase Prophase Metaphase Anaphase Telophase
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Review of Cell Reproduction
Mitosis & Cytokinesis Review Link:
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Check out Cells Alive! and Biology in Motion from class website for mitosis review.
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III. Sex Cell Formation - Meiosis
Chromosome Number Humans have 23 pairs of chromosomes, fruit flies have 4 pairs Homologous = chromosomes that each have a corresponding chromosome from the opposite-sex parent Diploid (2N) = two sets of chromosomes Haploid (N) = one set of chromosomes Fruit fly chromosomes Human chromosomes
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Meiosis I (reducing # of chromosomes)
Phases of Meiosis Meiosis = process of forming sex cells, “reduction and division” Meiosis I (reducing # of chromosomes) Begin with diploid cells (2N) Chromosomes have already been replicated Each chromosome pairs up with its homologous chromosome to form a tetrad (contains 4 chromatids) In prophase I in a tetrad, chromatids cross over one another, exchanging genetic info. (crossing-over) DRAW Fig , pg. 276 Homologous chromosomes are pulled to opposite sides of the cell, new haploid daughter cells are formed (N) Homologous chromosomes
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Meiosis I Homologous chromosomes Crossing-over
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Meiosis II Prophase II Metaphase II Anaphase II Telophase II
Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original. The chromosomes line up in a similar way to the metaphase stage of mitosis. The sister chromatids separate and move toward opposite ends of the cell. Telophase II Meiosis II results in four haploid (N) daughter cells.
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Body cell in a reproductive organ
father’s chromosome mother’s chromosome chromosomes copied crossing-over 4 unique gametes
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Meiosis II (division of chromosomes at centromere)
Meiosis II looks like mitosis except that crossing-over already occurred Chromosomes line up during metaphase Sister chromatids separate during anaphase At the end, you have 4 cells that are genetically different (ex: 4 unique sperm cells)
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C. Gamete Formation DRAW Fig. 11-17, pg. 278 Gamete = sex cell
***Use color to show crossing-over! C. Gamete Formation Gamete = sex cell Males produce sperm haploid each sperm cell can be involved in reproduction Females produce eggs cell divisions are uneven only one cell receives most of the cytoplasm other cells are called polar bodies
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IV. Regulating the Cell Controls on Cell Division
When cells come into contact with other cells they respond by not growing Controls on cell growth and cell division can be turned on and off With an injury, cells at edge of injury are stimulated to divide rapidly to begin healing
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Cell Cycle Regulators Regulators = respond to events to speed up or slow down cell cycle Cyclins = proteins that control the timing of the cell cycle in eukaryotic cells A sample of cytoplasm is removed from a cell in mitosis. The sample is injected into a second cell in G2 of interphase. As a result, the second cell enters mitosis.
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Growth factors – stimulate growth & division important in embryonic cells and wound healing
Uncontrolled Cell Growth Cancer = a disease of the cell cycle Cancer cells do not respond to signals that regulate growth of most cells Tumors = masses of cells that damage the surrounding tissue When a cancer metastasizes, cells have broken off the tumor and traveled to other parts of the body Known causes – smoking, tobacco, radiation exposure, viral infection Cancer cells do not respond to density dependent inhibition. Do not respond to restriction point, but sometimes stop dividing in the middle of any phase. Since 1951 cells from Henrietta Lacks (HeLa) have been dividing even without nutrients are said to be immortal. By contrast, most normal mammalian cells divide in culture about times before they stop dividing, age, and die off. Metastasizing occurs when the cancer cell surface is abnormal causing it to detach from the cellular matrix and spread to other tissues.
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