Notes: Cell Division

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Notes Cell Division the Cell Cycle (Ch. 12)
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• One of the major characteristics of a living
  thing is the ability to GROW.
• What does growth mean in terms of the cell?
  Bigger cells or more cells?

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• Why more cells?
• cell size is limited by its surface area to
  volume ratio (SAV)
• if a cell gets too large, it wouldnt be possible
  for it to get oxygen/nutrients in and wastes out
  by diffusion

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Cell Division

• In simple terms 1 cell divides into 2 new cells

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3 main stages of the Cell Cycle

• Interphase
• longest stage (90) preparation for cell
  division
• Mitosis (10)
• nucleus divides into 2 nuclei, each with the same
  and kind of chromosomes (DNA) as the parent
  cell
• Cytokinesis
• cytoplasm divides forming 2 distinct cells

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Cell Cycle
G1 growth (producing proteins organelles) S
DNA Synthesis (duplicated) more growth G2
growth completes preparation for division
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• MITOSIS the division of the nucleus
• Why is it important that the nucleus divides?
• it stores the DNA (information of life)
• all new cells need this information

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• Chromosomes tightly coiled chromatin (DNA)
  consist of 2 identical chromatids (sister
  chromatids) which are connected in the center by
  a CENTROMERE

a human cell entering mitosis contains 46
chromosomes (DIPLOID number)
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chromosome
centromere
chromatin
DNA
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How Does Chromatin Coil so Tightly?

• Chromatin wraps around 8 histone proteins
• A second type of histone (H1) holds the
  nucleosome beads together to increase
  compaction further

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Next the stages of MITOSIS!
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Mitosis is one, continuous event, but it can be
described as happening in 5 phases

1. Prophase
2. Prometaphase
3. Metaphase
4. Anaphase
5. Telophase

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Remember, the cell is coming out of Interphase
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PROPHASE

• chromatin condenses chromosomes become visible
• Centrosomes/ centrioles separate and start to
  move to the opposite sides of the nucleus

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PROMETAPHASE

• nuclear envelope breaks down and the nucleolus
  disappears
• spindle fibers (from centrioles) connect to
  chromosomes at their centromeres (kinetochore)

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METAPHASE

• chromosomes line up in the center of the cell
  (metaphase plate)
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• fibers connect from the poles (end) of the
  spindle to the centromere/kinetochore of each
  chromosome

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ANAPHASE

• centromeres split, causing the sister chromatids
  to separate, becoming individual chromosomes
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• chromosomes are pulled apart to opposite ends of
  the cell

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TELOPHASE

• chromosomes uncoil into chromatin
•  
• new nuclear envelope forms around the chromatin
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• spindle breaks apart
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• nucleolus reappears in each new nucleus

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Finally CYTOKINESIS

• in animal cells cell membrane pinches in
  divides (cleavage furrow)
• in plant cells a cell plate (new cell wall)
  forms

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Then the cell returns to Interphase and the
process continues
One More Time!
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Which of the following processes take place
during interphase?
SL

1. Cell division
2. Cell division Active Transport
3. Active Transport Protein Synthesis
4. Active Transport, Protein Synthesis, Replication
   of DNA

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How are all cells formed?

1. By cell division
2. By mitosis
3. By fragmentation
4. By cytokinesis

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Chromatids are

1. Made of microtubules
2. Bacterial chromosomes
3. Strands of duplicate genetic material
4. Supercoils of protein

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What is the correct order for Mitosis?

1. Interphase, Prophase, Prometaphase, Metaphase,
   Anaphase, Telophase
2. Prophase, Prometaphase, Metaphase, Anaphase,
   Telophase
3. Telophase, Anaphase, Metaphase, Prometaphase,
   Prophase
4. Interphase, Prophase, Prometaphase, Metaphase,
   Anaphase, Telophase, Cytokinesis

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This cell is in which phase of Mitosis?

1. Prophase
2. Prometaphase
3. Anaphase
4. telophase