Chapter 7How Cells Divide

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Chapter 7-How Cells Divide
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Chapter 7-How Cells Divide

• Cell division- process which cellular material is
  divided btw. two new daughter cells.
• In many celled organisms, it is the way the
  organism grows/repairs itself
• When cell reaches certain metabolic state, it
  divides.
• New cells are similar to parent because it
  inherits exact hereditary information
• 1/2 of the parent cells cytoplasm and organelles
• Initiated when cell reaches critical size

• One-celled eukaryote, Paramecium cell division
  may occur every few hours

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http//www.sirinet.net/jgjohnso/reprod.html
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Prokaryotes

• Most of the hereditary material is single, long,
  circular molecule of DNA. (a chromosome).
• 2 daughter chromosomes attach different spots of
  interior of cell membrane.
• As membrane elongates, chromosomes separates,
  cell membrane pinches inward, new cell wall forms

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Prokaryotes
http//www.sirinet.net/jgjohnso/reprod.html
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Cell Division in Eukaryotes-Cell Cycle

• 1000x more DNA
• linear with distinct chromosomes (the human
  somatic cells- 46), more organelles
• Interphase-
• G1, S, G2- replicates and synthesizes histones/
  proteins, organelles
• assembly of structures
• G1-
• follows cytokinesis, intensive biochemical
  activity. Cell size, enzymes, ribosomes,
  mitochondria, cytoplasmic molecules increase
• Some created from de novo (from
  scratch)-microtubules, actin filaments,
  ribosomes- protein subunits

• 2 centrioles (not found in fungi/plants)
  separate begin replicating (finish job in G2)
• --Mitochondria/chloroplasts replicate (own
  chromosomes)

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• Synthesis phase- DNA replication/histones
• Takes the most time to complete
• G2, newly replicated chromosomes, coil/condense
  for complex movements of chromsome in mitosis
• Completed contriole pair outside nuclear envelope
• Assemble special structures
• Finish replication of centrioles

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Regulation of the Cell Cycle

• RBC 25 trillion in adult
• - produce 2.5 million each second (critical to
  divide at a sufficient rate in multicellular
  organismscancer)
• Cells stop growing-
• 1. environmental factors (depletion of nutrients/
  change in temp)
• 2. Contact (density-dependent) inhibition-stop
  when they are touching in late G1 phase
• R restriction point? quickly to S phase
• Hypothesis- passing R point requires specific
  concentration of protein in small quantities sign
  of suitable size/metabolic state
• Stimulatory/inhibitory growth factors,
  synthesized by the cell itself

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• Chromosome condense after S phasechromatids
  joined by centromere attached to kinetochore
  (microtubules attach to this)
• Spindle-assembly of microtubles. Tubulin
  dimerscytoskeleton
• Polar fibers (each pole to center)
• Kinetochore fibers (attached kinetochores of
  chromosomes)
• Aster- short extend from centrioles, brace poles
  of spindle against cell membrane withoutcell
  wall

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• Spindle is dissembled after cell division,
  cytoskeletal network of microtublues reassembled
• interchangeablility of basal bodies/centriole
  (Chlamydomonas)
• Staining region around centrioles, now thought to
  be microtubule center

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• Interphase- chromosomes visible thin strands of
  threadlike material (chromatin) within the
  nucleus under light microscope
• Chromosomes- pairs of identical
  replicaschromatids, held at centromere
• Spindle forms (btw the centrioles, animal cells),
  extend to poles
• Fibers attach to chromatids at kinetochores
  (protein structures with centromeres)

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Interphase
http//www.gpc.edu/vmicheli/biol107/mitosis.htm
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Prophase- About 10 Minutes!Longest phase of
mitosis

• (1)Prophase (longest)
• -chromatin condensed individual chromosomes
  visible
• - Cell is more spheroid, microtubules are
  disassembled from cytoskeleton for formation of
  spindle. Cell takes on a spheroid shape
• -Centriole move apart form spindle (aster)
• - Ends with chromosome fully condensed,
  centriole pairs at poles, polar fibers formed,
  kineticore fibers formed.
• -Breakdown of nuclear envelope ( resembles ER
  )/disappearance of nucleoli

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Prophase
http//www.gpc.edu/vmicheli/biol107/mitosis.htm
http//staff.jccc.net/pdecell/celldivision/mitosis
1.html
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• (2) Metaphase chromatid pairs move to center,
  arranged equatorial plane
• (3) Anaphase rapid! sister chromatids separate
  at centromere,
• each chromatid move to opposite pole by
  kinetochore fibers.
• (4) Telophase chromosomes opposite ends
• tublin dimers disperse, nuclear envelope forms.
  Spindle breaks down, chromosomes uncoil and
  extend, nucleoli reappear.
• Theories of Movement in Chromosomes -
• --kinetochore fibers lengthen in prophase,
  shorten in anaphase
• --Material added-pushing/pulling together
• --Microtubles are protein arms with enzyme energy
  reactions

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Metaphase
http//www.gpc.edu/vmicheli/biol107/mitosis.htm
http//staff.jccc.net/pdecell/celldivision/mitosis
1.html
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Anaphase
http//www.gpc.edu/vmicheli/biol107/mitosis.htm
http//staff.jccc.net/pdecell/celldivision/mitosis
1.html
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Telophase
http//www.gpc.edu/vmicheli/biol107/mitosis.htm
http//staff.jccc.net/pdecell/celldivision/mitosis
1.html
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• (5)Cytokinesis- (division of cytoplasm)
• Animal- constrictions by actin filaments to form
  a furrow
• Plants- cytoplasm divided by vesicles
  (polysaccharide-containing vesicles from Golgi
  complex) to form cell plate.
• -Layer of polysachharides impregnated with
  pectins (forming the middle lamella), cellulose
  against outer surface
• Spindle might play a role division of cytoplasm.
• Actin filaments-constriction, purse string to
  pinch apart.
• Exact copy parent cell, half cytoplasm/organelles

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Cytokinesis
http//www.sirinet.net/jgjohnso/reprod.html
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Liver cells

• Are capable of dividing to replace liver mass
  that has been surgically removed

http//www.pennhealth.com/hup/transplant/liver/abo
ut_liv_don.html
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Chloroplast Mitochondria

• Have their own chromosomes

http//www.agen.ufl.edu/chyn/age2062/lect/lect_04
/lect_04.htm