Cell Division

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Cell Division

• Multicellular organisms
• Important in growth and development
• Single celled organisms
• Important for reproduction
• Goals
• To create 2 identical daughter cells

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Genetic Material Equally Distributed

• What has to occur in order for genetic material
  to be equally distributed?
• Each new cells contains the total number of
  chromosomes as the parent cell
• DNA has to replicate
• Before we talk about replication we need to
  understand more about DNA

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The Structure of DNA

• Double Helix
• Sugar Phosphate Backbone
• Made of nucleotides

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p
NUCLEOTIDES
base
base
sugar
sugar
p
p
base
base
sugar
sugar
p
Bases Guanine Cytosine Thymine - Adenine
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Helicase binds to the DNA molecule Causing the
DNA helix to break apart
REPLICATION
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DNA Polymerase binds to the DNA strands
Once DNA Polymerase reaches the end of the
strand it moves back to the top.
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DNA polymerase assembles nucleotides The new DNA
strands grow in length
DNA polymerase moves in the forward
direction This causes one of the new strands to
be in pieces
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As the new DNA strands grow Ligase bonds the
fragments together
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Once DNA polymerase reaches the end the two new
strands are finished
The fragmented strand is now whole due to Ligase
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DNA Replication
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Before we go on to cell division

• What is the structure of DNA?
• How are the bases paired?
• What is the function of DNA?
• Replicate the following chain
• TAC TTG AAA TGA CCC ACG ACT
• AUG AAC TTT ACT GGG TGC TGA

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Back to Cell Division

• Cells pass through a life cycle of 5 phases
• In single-celled eukaryotes,
• cell cycle is the major mechanism for asexual
  reproduction
• In multicellular eukaryotes,
• Development
• Growth

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Cell Cycle Overview

• Key Events
• Cell grows (interphase)
• DNA doubles (interphase)
• Nucleus divides (prophasetelophase)
• Cyotplasm divides (telophase)

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Mitosis an Overview

• Interphase each chromosome is uncoiled and in an
  unreplicated state

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Mitosis an Overview

• interphase, each chromosome is replicated. The
  replicated chromosome consists of two sister
  chromatids attached at the centromere.

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Mitosis an Overview

• At the beginning of mitosis, the chromosomes coil
  and become visible (still Interphase). Note that
  the chromosome is still in a replicated state,
  with a sister chromatids attached at the
  centromere.

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Mitosis an Overview

• Anaphase the centromere splits, the sister
  chromatids separate and become daughter
  chromosomes, the daughter chromosomes move to
  opposite sides of the cell.

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Mitosis an Overview

• At the end of mitosis, the chromosomes on each
  side of the cell uncoil and form two new,
  identical nuclei. (telophase)

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A.     Prophase

• 1. Chromosomes coil up and become individually
  visible.
• 2. The nuclear membrane disappears
• 3.  The mitotic spindle will form between the
  centrosomes.
• 5. microtubules attach to the centromere of each
  sister chromatid

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A.     Metaphase

• 1.  Chromosomes line up on the middle of the
  spindle.
• 2.  Each chromosome has microtubules attached to
  the centromere of each of its sister chromatids.
  

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B.     Anaphase

• 1.  Chromosomes move to opposite ends of the
  cell. One chromatid from each chromosome goes to
  each end of the cell.
• Use spindel fibers to do this
• a)  Why cant DNA fragments without a centromere
  be passed on to further generations?
• b) Why cant chromosomes have more than one
  centromere?

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A.     Telophase

• 1. Chromosomes reach the opposite ends of the
  cell.
• 2.  Chromosomes uncoil
• 3. The spindle disintegrates,
• 4.   The nucleolus reappears
• 5.  The cytoplasm divides in a process known as
  cytokinesis.
• a)  using either a cell plate or cleavage furrow
• b). This produces two cells each identical to
  the original cell (except, of course for errors
  in DNA duplication).

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Mitosis an Overview

• During what stage of the cell cycle do the
  drawings take place?
• What is a chromosome? A chromatid? A sister
  chromatid? A daughter chromosome? And in what
  stage of the cell cycle do we find each?