Cell division

Biology is the only subject in
which multiplication is the
same thing as division…
2007-2008
The Cell Cycle:
Cell Growth, Cell Division
2007-2008
Where it all began…
You started as a cell smaller than
a period at the end of a sentence…
And now look at you…
How did you
get from there
to here?
Getting from there to here…
 Going from egg to baby….
the original fertilized egg has to divide…
and divide…
and divide…
and divide…
Recap: Why do cells divide?
 For reproduction

asexual reproduction
 one-celled organisms
 For growth

from fertilized egg to
multi-celled organism
 For repair & renewal

replace cells that die
from normal wear &
tear or from injury
amoeba
Making new cells
 Nucleus
chromosomes
 DNA

 Cytoskeleton

centrioles
 in animals

spindle fibers
DNA
Nucleus
 Function
chromosome
protects DNA
 Structure


histone protein
nuclear envelope
 double membrane
nucleolus
nuclear envelope
Centrioles
 Cell division
in animal cells, pair of centrioles
organize spindle fibers
 guide chromosomes in mitosis

Chromosome structure: Folding of DNA
chromatin loop
DNA
Histone (protein)
chromosome
DNA double helix is
wrapped around proteins
Getting the right stuff
 What is passed on to daughter cells?

exact copy of genetic material = DNA
 Mitosis (IPMAT)

organelles, cytoplasm, cell membrane,
enzymes
 cytokinesis
chromosomes (stained orange)
in kangaroo rat epithelial cell
notice cytoskeleton fibers
Overview of mitosis
interphase
prophase
I.P.M.A.T.C.
lining up…
cytokinesis
metaphase
anaphase
telophase
Interphase
 90% of cell life cycle

cell doing its “everyday job”
 Produces proteins & enzymes

prepares for duplication if triggered
I’m working here!
Time to divide
& multiply!
green = key features
Interphase
What you see:
 Nucleus well-defined

DNA loosely packed in
long chromatin fibers
What happens: Prepares
for mitosis

replicates
chromosome (DNA) (to
make 2 identical
copies)
doublestranded
mitotic human
chromosomes
Mitosis
 Dividing cell’s DNA between
2 daughter nuclei

“dance of the chromosomes”
 4 phases
prophase
 metaphase
 anaphase
 telophase

green = key features
Prophase
 Chromatin condenses
visible chromosomes
Centrioles move to opposite
poles of cell
Spindle fibers cross cell to
coordinate the movement of
chromosomes
Nucleolus disappears
Nuclear membrane breaks
down





green = key features
Metaphase
 Chromosomes align
along middle of cell
meta = middle
 helps to ensure
chromosomes
separate properly

 so each new nucleus
receives only 1 copy
of each chromosome
green = key features
Anaphase
 Chromosomes separate
at centromere

pulled and move to
opposite poles
 Poles move farther apart
green = key features
Telophase
 Chromosomes arrive at
opposite poles
daughter nuclei form
 chromosomes disperse

 no longer visible under
light microscope
 Cytokinesis begins

cell division
Cytokinesis
 Animals
constriction belt
around equator
 Cytoplasm &
organelles
separate into
roughly equal
parts

 cleavage furrow
forms
 splits cell in two
 like tightening a
draw string
Mitosis in whitefish blastula
Mitosis in animal cells
Cytokinesis in Plants
 Plants
cell plate forms
 new cell wall laid
down between
membranes

 new cell wall fuses
with existing cell wall
Cytokinesis in plant cell
onion root tip
Any Questions??
Pull out a microviewer & then
work through your mitosis
worksheet