1. Cell Size and the Cell Cycle
Why do cells divide?
2 reasons
The larger a cell becomes:
the more demands are placed on its DNA.
the more trouble a cell has moving nutrients and wastes across the cell membrane.

2. 1. DNA Demand
As cells grow larger they usually do not make extra copies of their DNA.
Therefore, as a cell grows, there is greater demand placed on the information contained in its DNA.
In time the cell would not be able to keep up with the demands for information from its DNA.

3. Surface area to volume ratio
2. Cell Transport Issues
As cells grow larger it becomes more difficult to efficiently move materials in and out of the cell by diffusion.
The smaller a cell, the larger the surface area to volume ratio; large surface area to volume ratios makes cells efficient.
Cell Size
1x1x1 cm
2x2x2
3x3x3
Surface Area
6cm2
24cm2
54cm2
Volume
1cm3
8cm3
27cm3
Surface area to volume ratio
6:1
3:1
2:1

4. Cell Division
when a cell becomes too large it divides, creating two new “daughter” cells through cell division
DNA is replicated 1st
(each new daughter cell will get a copy)
cell size is reduced

5. Cell Cycle
repeating sequence of cell growth and division during an organism’s lifetime
cells grow, prepare for division, and divide to form two daughter cells, each of which then begin the cell cycle again.
regulated by proteins that receive and send signals (checkpoints in the cell cycle)

6. Cell Cycle
Phases
G1 Growth
S Synthesis
G2 Growth
M Cell Division

7. Cell Cycle Phases G1 Growth S Synthesis G2 Growth Interphase
G2 Growth
M Cell Division
Interphase

8. Interphase every phase except ‘M’ Phase (cell division)
cells spends most of their time in interphase

9. Interphase G1 First Growth Phase S Synthesis Phase
increase in size and make new proteins and organelles
S Synthesis Phase
chromosomes (DNA) are replicated
G2 Second Growth Phase
preparation for mitosis
shortest phase
organelles and molecules required for cell division are produced

10. M Phase Cell Division divided into two parts Mitosis Cytokinesis
division of the cell’s nucleus
Cytokinesis
division of the cell’s cytoplasm