Download Chapter 8: Cell Growth and Division

Chapter 8: Cell Growth
and Division
Cell Growth
Describe cell growth
Define cell division
Relate cell growth to cell division
Why do cells divide?
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To
To
To
To
reproduce
grow bigger
repair injuries
become more efficient
Limits of Cell Growth
1. Volume grows faster than surface area
2. Therefore a larger cell has a more difficult time
getting stuff into (oxygen & nutrients) and out of
(wastes) the cell
3. SOLUTION: Cell Division
Rates of Cell Growth
1.
Vary depending on cell
type
2. E. Coli divide every 30
minutes
3. Some cells take much
longer to divide or
“stop” dividing for a
while
Controls on Cell Growth
1. Some cells rarely/never divide – nervous and heart
cells
2. Some cells divide daily – skin and digestive tract cells
3. STOP switch: cells stop growing when they bump
into each other
4. ON switch: cut or break in tissue cause cells to grow
rapidly (but growth slows as healing reaches
completion)
Cell Division: Mitosis & Cytokinesis
Define mitosis and cytokinesis
Describe the cell cycle and the changes
that take place during interphase
Discuss the events and significance of
mitosis
Chromosomes
1.
Chromosomes:
o
“colored body”
o
seen only when the cell divides
o
contain genetic info in the form of
DNA
o
are coiled chromatin
2.
Composition of Chromatin
o
Make up chromosomes
o
Composed of DNA and protein called
histones (helps to condense the
DNA)
o
DNA in a chromosome is 10,000x
longer than the chromosome itself
o
Must condense in order to separate
correctly during mitosis
Chromosome Structure
o
Can only see chromosomes
during division
Each chromosome
replicates and is paired as
sister chromatids joined
at a centromere
Human cell = 46
chromosomes (2n)
o
o
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“n” number = 23 = “haploid”
2n = 46 = “diploid”
4n = 92 (during interphase)
Body cells (aka somatic cells)
= 2n = 46
Sex cells (aka eggs & sperm)
= n = 23
The Cell Cycle
1.
Growth, prepares for
division, divides (anywhere
from 6 hours to 100 days)
2.
3 Parts
o Interphase
o Mitosis (PMAT) - few
minutes to several days
o Cytokinesis
Interphase – 3 stages
 More than 90% of the life of a
cell is spent in this phase
 G1: cell growth, development,
and protein production (longest)
 S: “Synthesis”, DNA replication
 G2: Organelles replicated
(shortest)
 Note: DNA exists as chromatin
(no chromosomes yet)
Mitosis - Prophase

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Longest phase of MITOSIS (5060 % of total time required for
mitosis)
Nuclear membrane starts to
disintegrate
Chromosomes condense (become
visible) – seen as 2 identical
chromatids lying side by side held
together by centromeres
Centrioles move to opposite poles
Spindle fibers grow from
centrioles, attach at centromeres
Mitosis – Metaphase
 Chromosomes attach
to the spindle fibers
 Chromosomes line up
in the middle (aka
equator)
 Spindle fibers run
from centrosomes to
centromeres of the
chromosomes
(hint “m”=middle)
Mitosis - Anaphase
 Centromeres split
 Spindles retract and pull
sister chromatids apart
 Chromosomes move to
opposite poles (toward
centrioles)
(hint “a” = away)
Mitosis - Telophase
 Chromosomes cluster at
poles
 Chromosomes uncoil – back
into chromatin
 Nuclear envelope reforms
around each new nuclei
 Mitosis is done
 Cell membrane begins to
pinch in the middle
Cytokinesis

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Cell membrane moves inward and pinches in the middle forming
two identical cells
In plant cells – a cell plate (eventually becomes the cell wall)
and cell membrane appear separating the 2 new cells
There are now 2 identical cells – same DNA, etc.
http://media.pearsoncmg.com/bc/bc_camp
bell_concepts_5/media/assets/interactive
media/activityshared/ActivityLoader.html?c
6e&12&03&8B%20Mitosis%20and%20Cyt
okinesis%20Animation
http://media.pearsoncmg.com/bc/bc_camp
bell_concepts_5/media/assets/videos/Ani
malMitosis-V.html
Pop Quiz????
1.
2.
3.
4.
What is the main goal of cell division?
What are the 3 phases of interphase?
What are the 4 phases of mitosis?
A cell has 12 chromosomes. At the end
of cell division how many cells will there
be?
5. A cell has 12 chromosomes. At the end
of cell division how many chromosomes
will be in each cell?