Transcript Mitosis makes sure the nucleus is copied exactly

Cell Reproduction
The Cell cycle:
• Just as you have a distinct life cycle, so do
cells.
• You spend most of your life growing and
maturing, and only a small portion of your
life reproducing.
• The same is true for cells.
Why are more cells needed?
•
•
•
•
Growth
Repair after injury
Replacement of worn out cells
In simple organisms a form of cell division
is used for reproduction!
• Grrr.....
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Cell Cycle
4
•
http://www.bdbiosciences.com/research/apoptosis/analysis/index.jsp
INTERPHASE
• Phase between cell
division... G1...S...G2
• Cell grows and does
its job
• DNA is uncoiled and
invisible (chromatin)
• DNA copied during S
The process of cell division
includes two parts:
• Mitosis - comes first to copy the nucleus then
Cytokinesis will divide the cytoplasm and
organelles to form two daughter cells
• “I hit my toe sis!”
• Mitosis consists of many different stages
The most important part :
• Mitosis makes sure the nucleus is copied
exactly! Making sure the right number
chromosomes end up in both cells.
• You have 46 chromosomes in every cell
• Thus each cell must make a copy of each
chromosome before it divides
Mitosis Stage 1:
PROPHASE
• nuclear membrane breaks
down
• Chromatin wind to become
visible chromatids
• chromatids (pairs of
chromosomes) stay
attached by a centromere.
• Centrioles (poles) appear
and move to opposite sides
of cell
• Spindle fibers form
between poles
Chromatids
• Two identical
chromosomes
joined at a
centromere
CHROMOSOME
CENTROMERE
SISTER COPY
Stage 2:
Metaphase
• Chromotids attach to
spindle fibers
• Chromotids line up on
midline (equator) of
cell (meet in middle)
Stage 3:
Anaphase
• Chromatids separate
and move to opposite
ends of the cell
• Centromere splits in
half
Stage 4:
Telophase
• Spindle disappears
• Chromosomes unwind
and become less
visible
• Nuclear membranes
form around the new
sets of chromosomes
• Cell begins to pinch
into two
• Mitosis ends with 2
nuclei in a single cell
Cytokinesis
• The division of the
rest of the cell:
cytoplasm and
organelles - roughly in
half
• Two daughter cells
are formed when this
is complete
Cytokinesis
Cytokinesis = Division of the
cytoplasm and the organelles
 In animal cells, the cytoplasm “pinches
in” until the 2 new cells have formed

© 2006 STCC Foundation Press, content by Dawn A. Tamarkin, Ph.D.
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Cytokinesis in Plant Cells
Since the cell wall will not allow
“pinching inward” a cell plate grows
from the middle of the cell to the
outside.
 After the cell plate is complete, the cell
walls are build around it.

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© 2006 STCC Foundation Press, content by Dawn A. Tamarkin, Ph.D.
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