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The Cell Cycle
Why do cells divide?
Reproduction
Replace damaged cells/Repair
Allows organism to grow
Density Dependent Inhibition
- Space fills, division stops
- Smaller cells are more efficient at:
- Obtaining
O2
H2O
Nutrients (glucose
amino acids, etc.)
- Ridding themselves of
CO2
wastes
Mathematical Proof:
cm2
cm3
Surface Area
Volume
Compare:
1cm
Surface Area = 1x6 = 6
Volume
1x1x1 1
More surface area
per unit of volume
3cm
Surface Area = 1x6(9) = 54 = 2
Volume
3x3x3 27 1
Less surface area
per unit of volume
Cell Cycle
So cells divide to stay small and efficient.
Let’s look at their life cycle:
G Phases =
intense growth
intense activity
S Phases =
DNA synthesis
Chromosome
division and
separation
How long does
this all take?
Depends on the
type of cell!
Skin cells – 2 or less hrs
Digestive – 6 hrs
Nerves – don’t
Mitosis: Cell division
Interphase: G1, S, G2
Chromosome Changes During
Cell Cycle
Chromosome
Sister Chromatids
joined by a
Centromere
Chromosomes
headed for 2
separate
daughter cells
Chromatin
Cell Division
Cell Division occurs in two ways:
to produce two different kinds of cells
for two different functions
Mitosis
produces genetically identical daughter cells that
will take over the job of the parent cell
Meiosis
produces genetically different cells that will
be used in sexual reproduction,,,egg + sperm
Mitosis
Occurs in 4 (5) stages:
Prophase
Metaphase
Anaphase
Telophase
(Cytokinesis)
Describe changes involving DNA
Describes changes involving
cytoplasm and the rest of the cell
Interphase
Cell is full sized
Nucleus is intact
DNA has already been replicated
Centrioles (animal cells only) are
prepared to assist in division
Animal Cell
Plant Cell
Centrioles
Prophase
Animal Cell
Chromosomes form
Nuclear envelope breaks up
Nucleolus breaks up
Spindle apparatus forms
Centrioles (animal cells only) move
to opposite ends of the cell
Plant Cell
Early
Late
Metaphase
Animal Cell
Chromosomes line up in the middle of the cell
Centrioles (animal cells only) are as far apart as possible
Spindle attaches to centromeres
Plant Cell
Anaphase
Animal Cell
Sister chromatids separate
Spindle shortens
Cytokinesis begins
Animal Cells = “pinching”
Plant Cells = cell plate forms
Plant Cell
Telophase
Animal Cell
Chromosomes have moved to opposite ends of the cell
Chromosomes begin to unwind into chromatin
Nuclear envelope begins to reform
Spindle apparatus dissociates
Cytokinesis continues
Animal Cells = pinching more
Plant Cells = cell plate grows until wall is complete
Plant Cell
Early
Late
Cytokinesis
Cell will separate throughout anaphase and telophase
Daughter cells result; half the size as parent cell at the end of G2
Animal Cell
Plant Cell