Cell Reproduction

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Cell Reproduction

• Chapter 8

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Cell Division

• A basic feature of living things is the ability
  to reproduce themselves
• Unicellular organisms produce a new individual
• Multicellular organisms create new members
• Cell division can occur for several reasons
• Create new individuals, reproduction
• Replace worn out cells
• Repair damage

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• Eukaryotes and prokaryotes differ
• Prokaryotes with simpler structure binary
  fission
• Cell divides into two
• Eukaryotes the nucleus must divide Mitosis
• Makes exact copy clone - of parent cell
  Identical daughter cells

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Binary fission 1st, DNA must all be copied so
each cell gets the same blueprint. Then the cell
splits into two cells
http//www.anselm.edu/homepage/jpitocch/genbio/bin
fission.JPG
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Eukaryotic cell division

• More complicated
• More DNA, packaged in pieces chromosomes
• Chromosomes come in pairs
• homologous chromosomes
• Nuclear membrane in the way
• Microtubules used to pull chromosomes around

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Homologous chromosomes
Same, but not identical.
Karyotype analysis
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Cell cycle

• The cell doesnt suddenly decide to divide and
  poof, mitosis happens.
• The activities of the cell can be described as a
  cell cycle.
• Overview of the cells activity
• Interphase resting stage
• Mitosis nuclear division
• Cytokinesis division of the cytoplasm

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The Cell Cycle
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Interphase

• Cell is busy doing its job just not dividing
• Nerve cells spend most of life in interphase
• Cancer cells spend little time in interphase
• Three parts
• G1 or Gap 1 or growth phase
• S phase Synthesis of DNA cell is committed to
  division
• G2 or Gap 2

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Normally, DNA is wrapped around proteins
(histones) to make nucleosomes (beads on a
string). This is wound up to make a solenoid
which is looped around in the nucleus, appears as
chromatin.
For mitosis, DNA has to be wrapped up even
tighter so it can be easily divided up.
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Mitosis

• Refers specifically to division of the nucleus
• Four phases
• Prophase
• Metaphase
• Anaphase
• Telophase
• We look for things that are happening to break
  mitosis into steps, but it is one continuous
  process.
• PMAT

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Centrioles the puppet masters.
Themselves made of microtubules, they organize
the microtubules that attach to the chromosomes
and pull them to where they belong.
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Prophase

• Chromosomes wind up or condense
• 2 meters / cell
• Linked by centromere
• Sister chromatids pairs of identical chromosomes
• Nucleoli disappear mitotic spindle forms from
  the centrioles
• Mitotic spindle web of microtubules that
  attaches to DNA to control where it goes.

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Late prophase (also called Prometaphase)

• Nuclear membrane disappears
• Nuclear membrane would just be in the way.
• Chromatids attach to fibers of mitotic spindle by
  means of specialized structure called a
  kinetochore
• Review centromere is where sister chromatids
  attach to each other kinetochore is thepart of
  the centromere where the microtubules attach to
  the sister chromatids. Chromatids are identical
  pieces of DNA made during S phase of the cell
  cycle.

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Metaphase

• Chromosomes line up in the center of the cell at
  the metaphase plate a disc
• The next step of mitosis doesnt happen until ALL
  the chromosomes are lined up and ready to go.

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Anaphase

• Centromere splits
• Microtubles of mitotic spindle pull members of
  each pair of duplicate chromosomes to opposite
  sides of the cell.

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Telophase

• Mitotic spindle disappears
• Nuclear membranes form
• Chromosomes unwind
• In other words, everything does back to the way
  it was except now there are two nuclei, and the
  rest of the cell is dividing too.

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Cytokinesis

• Division of the cytoplasm
• Accompanies mitosis
• Begins in anaphase and finishes after telophase
• Animal cells form a contractile ring using actin
  one of the proteins found in muscles.
• Indentation is called the cleavage furrow
• Pinches the cells apart

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Plant cells

• Mitosis occurs in plants as in animal cells, but
  cytokinesis is different because of the plant
  cell wall.
• A disc of new membrane called the cell plate
  forms between the two cells during telophase and
  expands until it reaches the edges of the cell
  membrane.
• The new cells then make cellulose fibers to form
  new cell walls.

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What controls whether a cell divides?

• Cell size
• hormones
• Growth factors
• Cyclins proteins that increase and decrease
  during the cell cycle

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Much of what we know about how and why a cell
divides was learned from trying to understand why
cells lose control.

• Cancer is unregulated cell growth
• If we know what normally controls cell division,
  we can find out how it goes bad.
• Genes involved in cell regulation named from
  cancer studies
• Oncogenes genes that turn on division
• Oncology the study of cancer
• Tumor suppressor genes prevent unwanted cell
  division.

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Tumors - neoplasms

• Cells have lost control over cell division
• Multiply, often without stopping.
• Benign tumors grow only in one area
• Cancers invade local tissues (look like a crab)
  and can metastasize or spread to other areas of
  the body through the vascular or lymphatic systems

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Cancer cells lose contact inhibition.
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