# 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.

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 views: 25 posted: 7/22/2010 language: English pages: 7