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 r2; – volume is 4/3 ( 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.