I. Limits to Cell Growth A.Not enough DNA 1.As a cell increases in size it doesn’t make more DNA 2.If a cell grows too large, new organelles can’t get the instructions they need to function
B.Exchanging Materials: a cell must move nutrients and wastes across the cell membrane 1.Materials go in and out depending on surface area 2.Food & oxygen is used up depending on volume 3.Ratio of Surface Area to Volume a.to make it easier, think of the cell as a cube b.Surface area = length x width x # of sides Ex: 1cm x 1cm x 6 sides = c.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 d.As a cell gets larger, volume increases much more rapidly than surface area. 4.If a cell becomes too big, it cannot exchange materials across the membrane fast enough.
Cell Size Surface Area (length x width x 6) Volume (length x width x height) Ratio of Surface Area to Volume
II. Cell Division A.Chromosomes 1.Carries the genetic information from one generation to the next 2.Made up of DNA and proteins 3.Replicated prior to cell division forming two identical “sister” chromatids a.Chromatids are attached by the centromere Draw sister
B.Cell Cycle 1.cell cycle = series of events a cell goes through as it grows and divides 2.A cell grows, prepares for division, and divides to form two daughter cells, each of which begins the cycle again 3.Organized into phases: a.M phase – cell division 1)mitosis – nucleus division 2)cytokinesis – cytoplasm division b.Interphase 1)G 1 phase – cell growth, makes new organelles 2)S phase – DNA replication 3)G 2 phase – preparation for mitosis, more growth, makes more enzymes 4)a cell spends ~90% of its time in interphase
M phase G 2 phase S phase G 1 phase DRAW Fig. 10-4, pg. 245
C.Mitosis 1.Prophase a.chromatin condenses b.centrioles separate c.spindle forms (microtubules that help separate chromosomes) d.Nucleolus disappears, nuclear membrane breaks down 2.Metaphase a.chromosomes line up across the center of the cell on spindle
3.Anaphase a.sister chromatids separate at centromeres and move apart 4.Telophase a.chromosomes gather at opposite ends, new nuclear envelopes form
D.Cytokinesis 1.To complete the M phase, we must have cytokinesis = division of the cytoplasm of the cell 2.Animal cells - cell membrane is drawn inward until the cytoplasm is pinched into 2 new cells 3.Plant cells - cell plate forms midway between the divided nuclei; the cell plate gradually develops into a separating membrane
n Check out Cells Alive! and Biology in Motion from class website for mitosis review. n http://www.cellsalive.com/ http://www.cellsalive.com/
III. Sex Cell Formation - Meiosis A. Chromosome Number 1.Humans have 23 pairs of chromosomes, fruit flies have 4 pairs 2.Homologous = chromosomes that each have a corresponding chromosome from the opposite- sex parent 3.Diploid (2N) = two sets of chromosomes 4.Haploid (N) = one set of chromosomes Fruit fly chromosomes Human chromosomes
B.Phases of Meiosis 1.Meiosis = process of forming sex cells, “reduction and division” 2.Meiosis I (reducing # of chromosomes) a.Begin with diploid cells (2N) b.Chromosomes have already been replicated c.Each chromosome pairs up with its homologous chromosome to form a tetrad (contains 4 chromatids) d.In prophase I in a tetrad, chromatids cross over one another, exchanging genetic info. (crossing-over) DRAW Fig. 11-16, pg. 276 e.Homologous chromosomes are pulled to opposite sides of the cell, new haploid daughter cells are formed (N) Homologous chromosomes
Meiosis II Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original. Prophase II Metaphase II Anaphase II Telophase II 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. Meiosis II results in four haploid (N) daughter cells.
father’s chromosome mother’s chromosome 4 unique gametes crossing-over chromosomes copied Body cell in a reproductive organ
3.Meiosis II (division of chromosomes at centromere) a.Meiosis II looks like mitosis except that crossing-over already occurred b.Chromosomes line up during metaphase c.Sister chromatids separate during anaphase d.At the end, you have 4 cells that are genetically different (ex: 4 unique sperm cells)
C. Gamete Formation 1. Gamete = sex cell 2. Males p roduce sperm a.haploid b.each sperm cell can be involved in reproduction 3. Females produce eggs a.haploid b.cell divisions are uneven c.only one cell receives most of the cytoplasm d.other cells are called polar bodies DRAW Fig. 11-17, pg. 278 ***Use color to show crossing-over!
IV. Regulating the Cell A.Controls on Cell Division 1.When cells come into contact with other cells they respond by not growing 2.Controls on cell growth and cell division can be turned on and off 3.With an injury, cells at edge of injury are stimulated to divide rapidly to begin healing
A sample of cytoplasm is removed from a cell in mitosis. The sample is injected into a second cell in G 2 of interphase. As a result, the second cell enters mitosis. B.Cell Cycle Regulators 1.Regulators = respond to events to speed up or slow down cell cycle 2.Cyclins = proteins that control the timing of the cell cycle in eukaryotic cells
3.Growth factors – stimulate growth & division important in embryonic cells and wound healing 4.Uncontrolled Cell Growth a.Cancer = a disease of the cell cycle b.Cancer cells do not respond to signals that regulate growth of most cells c.Tumors = masses of cells that damage the surrounding tissue d.When a cancer metastasizes, cells have broken off the tumor and traveled to other parts of the body e.Known causes – smoking, tobacco, radiation exposure, viral infection