Cell Division

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Cell Division
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Background Info

• What, specifically does DNA really code for?
• Codes for Amino Acids that assemble to make a
  protein
• What is the normal appearance of DNA under a
  microscope?
• CHROMATIN (not chromosomes) LOOKS LIKE
  SPAGHETTI, OR A HAIRBALL
• What is the point of DNA tightening together into
  chromosomes before cell division?
• For organization before Cell Division occurs

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• How many chromosomes are in a human cell?
• 46 chromosomes 23 from mommee, 23 from daddio
• There are only 23 types of chromosomes
• Mitosis making identical copies of a nucleus
• Q What part of cell division does the definition
  of mitosis leave out?
• Among other things (1) the doubling of
  organelles, and (2) the cell actually splitting

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Mitosis creates two genetically identical
nuclei (2.5.5)(Mitosis is only part of the
cells life cycle)

• Cell Cycle (life of a cell) consists of
  (2.5.1)
• Interphase
• Mitosis
• Prophase
• Metaphase
• Anaphase
• Telophase
• Cytokinesis division of the cytoplasm

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• B. Interphase the longest phase an active
  growth period when many biochemical reactions are
  occurring (2.5.3)
• 3 stages of interphase
• G1 formation of new organelles (ribosomes,
  mitochondria, etc) transcription and translation
  of proteins
• DNA transcription making mRNA from DNA
• Translation making proteins from mRNA
• S DNA Replication
• G2 spindle fibers form chromosomes condense

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Interphase
NOTE diagrams are misleading because the DNA is
NOT really coiled up yet into chromosomes (which
is why transcription and DNA synthesis can occur)
A a C C
G1
B b d
D
MOM
DAD
Homologous pair of chromosomes
At this point, is the cell haploid or
diploid? Its diploid- there is a copy of each
chromosome from both parents.
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• Haploid or diploid?
• Still diploid- now with sister chromatids.
• Heterozygous or homozygous?
• Heterozygous for genes A, B, D
• Homozygous (dominant) for gene C.

S
A A a a C C
C C
B B b b d d
D D
G2 microtubules join to form the
spindle
CENTROMERE (the region joining 2 sister
chromatids)
2 chromatids (still one chromosome)
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C. Mitosis (2.5.4, 2.5.5)

• Prophase - Supercoiling of chromosomes

C C d d
a a b b
A A
C C D D
B B
Centriole (made of microtubules)

• Nuclear membrane breaks down
• Centrioles move to the poles
• (No centrioles in most plant cells animals
  only!)
• Spindle microtubules are growing
• DNA begins to coil into chromosomes

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Metaphase spindle microtubules attach to
centromeres at kinetochores chromosomes line
up at the equator on separate spindle
microtubules nuclear membrane has broken down
kinetochore
A A
B B
a a b b
(pole)
C C D D
(pole)
centriole
C C d d
equator
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Anaphase centromeres split and chromosomes move
toward the poles, pulled by spindle microtubules
sister chromosomes move to opposite poles
A B a b
C D C d
A B a b C D
C d
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ANAPHASE!!!!!
Spindle Fibers
Cytoplasm
A B A B
D d
A B A B
D d
Centrioles
Centrioles
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Telophase chromosomes reach the poles spindle
microtubules break down cytokinesis begins
during late telophase
PLANT ANIMAL
-forms a cell plate -forms a cleavage
furrow
-Nuclear envelope reforms
A a
C C

D B b
d
a C A
C b D B
d
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• D. Cytokinesis division of the cytoplasm to
  form two (identical) cells
• II. Differences in mitosis between plant and
  animal cells
• -plant cells do not have centrioles in animal
  cells they are found at each pole during mitosis
• -plant cells cannot form cleavage furrows and so
  they form cell plates

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• III. Reasons for mitosis (2.5.6)
• Growth
• Embryonic development
• Repairing damaged tissue
• Asexual reproduction
• IV. Tumor formation (2.5.2)
• Repeated, uncontrolled cell division
• Can happen in any organ, and can spread to other
  parts of the body (metastasis)
• When it causes disease it is considered a cancer