Cell Growth and the Cell Cycle

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					Cell Growth and the Cell Cycle

  Boy there are a lot of cycles: carbon
 cycle, ATP cycle, Calvin cycle, Krebs
                cycle…..
                 Cell Growth

• Recall that the cell membrane encloses the cell
• Cell size is limited due to the mathematical
  relationship between surface area and internal
  volume
• Volume increases as a cube function
• Surface area increases as a square function
• Why are small cells more efficient: recall the
  discussion on diffusion. Diffusion is faster over
  shorter distances
                The math of it
• For a sphere:
  – area is 4 p r2;
  – volume is 4p/3 ( r3 )


• For a cube:
  – area is L(W) x 6;
  – volume is LWH
               Cell Cycle

• Once cells reach a certain size they divide
• The cell cycle is a regular process of
  growing and dividing; the period of time
  between the beginning of one cell division
  to the beginning of the next cell division
• Thousands of events happen during the cell
  cycle but two are used as landmarks:
                 Cell Cycle
• There are four phases in the cell cycle
• Named with abbreviations for the phases:
  – G1 (first gap) most of the cells growth and
    activity in this phase
  – S (synthesis) cell duplicates its chromosomes
  – G2 (second gap) cell prepares for cell division
  – M (mitosis) cell divides
                 Cell Cycle
• One is cell division: cell divided into two
  independent cells (called daughter cells)
  – In eukaryotic cells this process is called mitosis
• Second landmark is the duplication of the
  chromosome
        Thought experiment:
• Take a cube cell 1 um x 1 um x 1 um and
  double it to 2 um x 2 um x 2 um

• Calculate how the volume changes relative
  to the surface area.