Ch. 8 – Cellular reproduction As a comparative / overview, organisms reproduce sexually and/or...
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Transcript of Ch. 8 – Cellular reproduction As a comparative / overview, organisms reproduce sexually and/or...
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
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=VlN7K1-9QB0http://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