Transcript Chapter 8
Ch. 8 – Cellular reproduction As a comparative / overview, organisms reproduce sexually and/or asexually • asexual reproduction – Offspring are produced by a single parent, without the participation of sperm or the transfer of genetic information • sexual reproduction – Transfer and integration of genetic information; i.e. fertilization of sperm and egg produces variety of offspring • In regards to Eukaryotic cells – unicellular organisms or cells of multicellular organisms… – asexual reproduction = ? • Mitosis – sexual reproduction = ? • Meiosis Cellular reproduction or division • Asexual reproduction – Genetic copies of single parent cell – “like begets like” – “clones” Prokaryotic asexual cellular division • Binary fission • Cell divides into two – Asexually • relatively simple …as simple as “one, two, three” • Cell replicates its genetic material – Single chromosome of DNA • Copies move apart • Growing membrane divides the cell Eukaryotic cellular division • Cells are larger • …more complex • Have more genes than prokaryotes – Grouped into multiple chromosomes in nucleus • before division begins – DNA condenses into thin loosely packed chromatin fibers which bind to histones (proteins) to form chromosomes • …before division – Chromosomes replicate into… – Sister chromatids joined at centromere • Two genetic copies • Eventually divides into two identical chromosomes Cell cycle multiplies cells • Most of the cycle is preparing for division – Interphase • Growth and replication – Cellular division process starts with mitosis Prophase, Metaphse, Anaphase, Telophase Interphase • Cell growth – Doubling most of its contents – Addition of two centrosomes in cytoplasm • Contain two centrioles • Microtubule organizing centers Prophase of Mitosis • Chromatin fibers coil forming discrete chromosomes – Joined at waist – Sister chromatids • Mitotic spindle forms – Microtubules extending from centrosomes • Centrosomes start to migrate to opposite poles Late Prophase • Nuclear membrane breaks down • Spindle fibers reach the condensed chromosomes – One end originating at centrosome, other attached to each sister chromatid Metaphase • Mitotic spindle fully formed • Centrosomes at poles • Chromosomes line up at equator Anaphase • Centromeres split, separating sister chromatids • Attatched spindle fibers shorten • Unattached spindle fibers lengthen – Push or elongate cell • Copied chromosomes migrate to poles Telophase • Reverse of prophase • Nuclear membranes begin to form around chromosomes • Mitotic spindle disappears • Cytoplasm prepares to divide = cytokinesis • …two daughter cells http://www.youtube.com/watch?v=VlN7K1-9QB0 http://www.youtube.com/watch?v=eFuCE22agyM Cytokinesis • Differs in animals and plants • Animal: – Ring of microfilaments contract • Pinching the cell • Like pulling a purse-string closed Plant cytokinesis • Cell wall material forms in center • Cell plate extends • Cell membrane follows • Cell plate fuses with cell walls