The Cell Cycle by 52u2QI8A

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									The Cell Cycle
     When do cells divide?
• Reproduction
• Replacement of damaged cells
• Growth of new cells
• In replacement and growth cell divisions
  how should daughter cells compare to
  parent cell?
• The daughter cells should be identical
  copies of the parent cell.
  How can identical daughter
         cells form?
• The genome must be copied and then
  divided such that each daughter cell
  gets one of the copies.
• Genome = all the genes in an organism
     Bacterial Reproduction
• How do bacterial cells reproduce?
Important terms in eukaryotic
        cell division
• Chromosome =
Important terms in eukaryotic
        cell division
• Chromosome = threadlike structures
  that are composed of DNA + protein
• replication =
 Important terms in eukaryotic
         cell division
• Chromosome = threadlike structures
  that are composed of DNA + protein
• replication = process whereby DNA is
  identically copied (before cell division)
• mitosis =
 Important terms in eukaryotic
         cell division
• Chromosome = threadlike structures
  that are composed of DNA + protein
• replication = process whereby DNA is
  identically copied (before cell division)
• mitosis = division of the nucleus
• cytokinesis =
 Important terms in eukaryotic
         cell division
• Chromosome = threadlike structures
  that are composed of DNA + protein
• replication = process whereby DNA is
  identically copied (before cell division)
• mitosis = division of the nucleus
• cytokinesis = division of the cytoplasm
• chromatin =
Important terms in eukaryotic
        cell division
• Chromosome = threadlike structures
  that are composed of DNA + protein
• replication = process whereby DNA is
  identically copied (before cell division)
• mitosis = division of the nucleus
• cytokinesis = division of the cytoplasm
• chromatin = DNA + protein complex
  that is thin and fibrous; it will condense
  into distinct chromosomes during cell
  division
• Chromatid =
• Chromatid = after replication the
  chromosome consists of 2 sister
  chromatids joined at the centromere.
• Centromere =
• Chromatid = after replication the
  chromosome consists of 2 sister
  chromatids joined at the centromere.
• Centromere = specialized region of the
  chromosome, where chromatids are
  joined. Each chromosome has one
  centromere.
The Cell Cycle
              Interphase
• 90% of cell cycle is spent in this phase
• G1 = first growth phase
• S = synthesis phase, DNA synthesis
  (replication) occurs here
• G2 = second growth phase
   G2 phase of Interphase in
         animal cells:
• Nuclear envelope is visible
• One or more nucleoli are present
• Centrioles are replicated and the 2 pairs
  are near nucleus
• aster forms around each pair of
  centrioles
• chromosomes are loosely packed into
  chromatin fiber, not distinguishable
General Overview of Mitosis
Late Interphase:
             Prophase:
• In the Nucleus:
• Nucleoli disappear
• chromosome fibers condense into
  discrete chromosomes
• each chromosome consists of 2 sister
  chromatids joined at the centromere
• In the Cytoplasm:
• mitotic spindle begins to form
• spindle consists of microtubules
  arranged between the centrosomes
• centrosomes move apart due to
  lengthening of microtubules
          Prometaphase:
• Nuclear envelope breaks apart
• each chromatid has specialized
  structure called kinetochore located at
  the centromere region
• knietochore microtubules (km) interact
  with chromosomes at the kinetochore
  region
• The km’s cause the chromosomes to
  move
• nonkinetochore microtubules radiate
  from each pole
                Metaphase
• Chromosomes move to the metaphase plate
  and line up there
• the centromeres of the chromosomes are all
  aligned on the metaphase plate
• each sister chromatid of one chromosome,
  has a kinetochore microtubule attached to it
  from opposite poles
• kinetochore microtubules + nonkinetochore
  microtubules = spindle fiber
             Anaphase
• Kinetochore microtubules shorten and
  non-kinetochore microtubules lengthen
• Centromeres divide and each
  chromosome has no sister chromatid
  component
• the shape of the cell elongates into an
  elipse
• chromosomes are pulled to the opposite
  poles
             Telophase
• Nonkinetochore microtubules continue
  to elongate the cell
• new daughter nuclei form at the two
  poles
• new nuclear envelopes are formed
  around the chromosomes
• nucleoli reappear
• chromosomes uncoil into chromatin
  fiber
• last phase of mitosis
            Cytokinesis
• Begins before telophase has completed
• evidenced by cleavage furrow in animal
  cells and cell plate in plant cells
Mitochondrial Division
         Evolution of mitosis:

                           Bacterial cells




Dinoflagelates;
chromosomes attach to
nuclear envelope.
                   Diatoms;
                   nuclear
                   envelope stays,
                   mcrotubules
                   inside nucleus




Most other
eukaryotes;
spindle forms
outside of
nucleus, and
nuclear envelope
breaks apart
Cytoplasmic Cell Signals in
 Regulation of Cell Cycle:
 Checkpoints
   in the cell
  cycle: If it
passes the G1
  checkpoint
 cell divides if
not enters G0
  phase and
    does not
     divide
Cyclin protein
levels fluctuate
according to cell
cycle stage.
When cyclin is
high the Cdk
attaches and
phsophorylation
leads to
breakdown of
nuclear
envelope. Later
MPF initiates
cyclin breakdown
             Cancer cells
• How does abnormal cell division of
  cancer cells differ from normal cell
  division?
• Cancer cells are not under density
  dependent inhibition
• Continue to grow until all nutrients are
  used up
• Cancer cells are immortal, do not
  shorten telomeres.

								
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