Cell Division and the The Cellular Basis of Inheritance

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Cell Division and the The Cellular Basis of
Inheritance

• Mr. Gawles Biology Class
• January 2006

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Section 9.1 All Cells Come From Cells

• Recall
• Characteristics of life and the Cell Theory
• Cells are the basic unit of life
• All cells come from pre-existing cells (i.e. one
  parent cell can divide into two daughter
  cells)
• Why do cells divide? Why dont they just keep
  getting bigger?
• To get bigger or divide lab

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How did you get here?

• Your body developed from a single cell formed
  from the union of a single egg and a single sperm
• How did that one cell give rise to the 200
  trillion cells that make up your body now?
• The answer is..MITOSIS! (or cellular division)

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Why do cells divide?

• Repair damage (maintenance)
• Growth and development
• Produce offspring
• So, the division of cells enables living things
  to repair damage, to grow, and to produce
  offspring
• Realize, while the production of new cells can
  result in growth and repair WITHIN organisms,
  cell division also has an essential role in the
  reproduction of ENTIRE organisms!

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Example of Cell Division

• Skin of your arm
• Outermost layer is actually dead
• Inner cells gradually replace outer cells
• This renewal of skin goes on your entire life

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Figure 9-1
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Reproduction

• While the production of new cells can result in
  growth and repair within organisms, cell division
  plays an important role in the reproduction of
  entire organisms
• Two major types of reproduction
• Asexual
• Sexual

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Asexual Reproduction

• In simple unicellular or in some multicellular
  organisms
• a single cell or group of cells duplicates its
  genetic material and then splits into two
  genetically IDENTICAL cells
• Inherit their DNA from only one parent
• Paramecium, sea stars, corals, plants
• AKA Cloning
• Brainstorm examples
• What would be the advantages to this?
• What would be the disadvantages?

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Sexual Reproduction

• Two parents are involved
• Genetic material (sex cells sperm and egg) from
  each parent combines
• Offspring are genetically different from either
  parent
• What are advantages and disadvantages to this
  mode of reproduction?

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See online activity 9.1
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The Cell Cycle

• At this moment, millions of your cells are
  dividing but the majority are not but are going
  about other activities
• How does cell division fit into the life of a
  cell?

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The Cell Cycle

• How often a cell divides depends upon the type of
  cell
• Some divide a lot, some less often, some
  specialized cells (muscle) do not divide at all
  (activity 9.2 page two)
• Eukaryotic cells that do divide undergo an
  orderly sequence of events known as the cell
  cycle
• Covers from the birth of a cell to the time the
  cell itself reproduces
• In humans, cells that reproduce daily take 10-20
  hrs

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The Cell Cycle of Eukaryotes

• Interphase (consists of G1, S, and G2 stages)
• 90 of the cell cycle is spent here
• Stage at which cell carries out metabolic
  processes and performs its functions within the
  organisms
• During this stage, a cell increases its supply of
  proteins, increases the of many of its
  organelles, and grows in size
• Also includes key events leading up to cell
  division including duplication of the DNA (this
  phase is known as S-Phase for synthesis)
• The interphase periods before and after the S
  phase are called the G1 and G2 phases (Ggap)
• Mitotic Phase (M)
• Stage where cell is actually dividing

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Figure 9-5
See nice animation here
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Figure 9-6
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Summary of Cell Cycle

• G1 Cell grows and carries out functions at end
  it reaches a checkpoint
• S nucleus enlarges and DNA/chromosomes replicate
• G2 Cell grows and prepares for cell division
  at end it reaches a checkpoint
• M Cell undergoes mitosis where nucleus and
  duplicated chromosomes and cytoplasm divide to
  form two daughter cells (IDENTICAL)
• Very accurate way of making identical copies of a
  large amount of genetic material only an error
  once every 100,000 cell divisions
• See online activity 9.2 page 1

See Online Activity 9.2 YOU BETTER KNOW THESE
COLD!!!!
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Some Basic Vocabulary

• Your genes are located in the cell nucleus
• A gene is a segment of DNA that codes for a
  protein
• When the cell is not dividing, the nucleus exists
  as a mass of Chromatin
• Chromatin (a combo of DNA and proteins)
• very long fibers too thin to be seen with a light
  microscope
• As the cell prepares to divide, its chromatin
  fibers condense becoming visible as compact
  structures known as chromosomes
• Each chromosome may contain thousands of genes
• of chromosomes in a eukaryote depends on
  species
• We have 46 chromosomes in our body

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Chromosome
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Some more vocabulary

• Before cell division occurs, a cell duplicates
  its chromosomes (copies its genetic material)
• Each chromosome now consists of two identical
  joined copies called sister chromatids joined
  tightly together at a region known as the
  centromere
• Eventually, when the cell divides, the sister
  chromatids separate from each other and are now
  known as a chromosome

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Figure 9-4
Happens in S phase of the Cell Cycle
Happens during MITOSIS