Cell division through mitosis allows cells to grow and replicate. As cells absorb nutrients and grow larger, they can no longer effectively absorb nutrients and remove waste, necessitating division. There are two main stages of a cell's life cycle - interphase where the cell grows and replicates its DNA, and the mitotic phase where the cell divides into two daughter cells through the stages of prophase, metaphase, anaphase and telophase. This process of mitosis ensures that the daughter cells are identical to the original parent cell and each other.

1. The Great Divide
05/04

2. Why Would a Cell Divide?
 As cells absorb nutrients and get larger, the
volume of the cell increases faster than the
surface area
 This means that a cell can no longer absorb
nutrients and get rid of wastes fast enough to
support its demands (volume)
 So what’s a cell to do? DIVIDE !!!!

3. Why Would a Cell Divide?
Besides growth a cell would also divide for:
 Repair or Replacement
 Cancer
Different cells divide at different rates:
 Most mammalian cells = 12-24 hours
 Some bacterial cells = 20-30 minutes

4. Getting Older…
 All cells are only allowed to complete a certain
number of divisions
 Then they die (programmed cell death)
How does cell division change over a lifetime?
 Childhood = cell division > cell death
 Adulthood = cell division = cell death
 The Later Years = cell division < cell death

5. Cell Cycle Tidbits
How long is one cell cycle?
 Depends on the cell- skin cells = ~24
hours, nerve cells = never after
maturity, cancer cells = very short
 Remember: every cell only has a certain
# of divisions it can undergo, then it
dies = apoptosis (programmed cell
death)

6. The Cell Cycle

7. Stages of the Cell Cycle
interphase (growth & replication of DNA)
mitotic phase (division of cell into 2 daughter cells)
 Cell spends
about 90% of
the time in
interphase
There are two stages to a cells life.

8. Interphase
 Divided into 3 phases:
 G1 (1st gap) = small cell is absorbing nutrients,
growing & doing its job.
 S (synthesis) = cell is continuing to grow &
duplicates its DNA.
 G2 (2nd gap) = cell keeps growing & doing its
job.

9. Mitosis: A Closer Look
DNA is all twisted up into a
Chromosome.
 During S phase the
Chromosome is copied.
 2 complete identical sets
of chromosomes.
 They are connected in
the middle by a
centromere.
 A single copied
chromosome is called a
Chromatid.

10. The Mitotic Phase
 Divided into 4 stages of Mitosis:
 Prophase
 Metaphase
 Anaphase
 Telophase
(+) PLUS
 Cytokinesis

11. Prophase
 Chromatids condense
becoming visible.
 Nuclear membrane dissolves
 The centrioles (an organelle
that makes microtubules)
appears and migrate to
opposite sides.
 spindle fibers start to form
between them
 http://www.biostudio.com/demo_freeman_dna_coiling.htm

12. Metaphase
 Chromosomes
line-up on the
metaphase plate
 Centromeres
are attached to
spindle fibers

13. Anaphase
 Spindle fibers contract
 Centromeres divide
 Sister chromatids are
pulled away from each
other towards the poles

14. Telophase
 The chromosomes
reach the poles
 Nuclear
membranes form
around the 2 new
nuclei

15. Cytokinesis
 The cytoplasm
distributed equally
between the 2 new
cells
 In animals, a
cleavage furrow
forms from outside
in
 In plants, a cell plate
forms from inside
out
Plant
Animal

16. What Mitosis Actually Looks Like
Interphase
Prophase Metaphase
Anaphase
Telophase
http://www.sci.sdsu.edu/multimedia/mitosis/mitosis_gif2.html
http://science.nhmccd.edu/biol/bio1int.htm

17. What Happens After Mitosis?
 The cell
returns to
interphase
 Chromosomes
uncoil back
into chromatin
 The cycle
repeats itself
over & over…

18. At What Stage Are Our Cells At In The Cell Cycle?
 Different cells can
be in different
stages
 Interphase
 Mitosis:
 Prophase
 Metaphase
 Anaphase
 Telophase
 Cytokinesis

19. The Guarentee
 The product of
mitosis is 2 cells
 The daughter cells
are identical to
each other & to the
mother cell
Mother
cell
Identical
daughter
cells
Why is this so
important?

20. The Daughter Cells
 In humans, the 2
daughter cells will have
46 chromosomes (23
pairs)
 Each chromosome is
said to have the same
gene sequence Identical
daughter
cells

21. The Beauty of Asexual Reproduction
 Mitosis is a
form of
asexual
reproduction
 New
individuals are
produced by 1
parent & thus,
are identical to
their parent
Mother
cell
Identical
daughter
cells
Runners produces by
strawberries
Cuttings from plants
Budding by hydra & yeast