The Cell Cycle and Mitosis:
“You Complete Me”
A process where one parent cell gives
rise to two daughter cells- exact
replicas of the original cell.
The Cell Cycle
• Every cell goes through a process of
growth, this is called the cell cycle.
• New cells start at G1 or Gap 1, go on
to an S phase (where DNA is
synthesized in preparation of
Mitosis), and then G2 or Gap 2
before Mitosis or Cell division.
• Some cells will no longer divide and
they exit the cell cycle in G1(neurons,
muscle cells, fat cells do this)
• As one cell enters Mitosis, two cells
exit which are exact replicas or
clones of the original “parent” cell.
Purpose: to replenish dead or dying
cells, to allow an organism to grow
and develop
Interphase
• This phase encompasses all of the G1,S, and G2 phases of the cell
cycle. The chromatin is diffuse.
• It may not look like much is going on here, but there is a lot of
activity because the cell must prepare for Mitosis: protein synthesis,
DNA synthesis, replication of other cellular structures too.
•
Onion root tip (on left side), whitefish (on right side)
Mitosis
• Mitosis occurs in order for
organisms to grow and
develop. In order to
replenish dead or dying
cells such as skin cells,
cells in the digestive tract
and in the fertilized egg.
• There are 4 main phases:
Prophase, Metaphase,
Anaphase, Telophase.
Cytokinesis (division of
the cytoplasm) follows
and one cell becomes
two.
Mitosis: Prophase
• Major processes during
this phase:
• Chromosomes condense
and form visible bodies
(DNA was replicated in S
phase)
• Nuclear envelope breaks
down
•
Onion root tip (top photo), whitefish (bottom
photo)
Mitosis: Metaphase
• Chromosomes attached
to spindle fibers line up in
the middle (the equator)
of the cell
• Spindle fibers attach to
the centromeres and
other places along the
chromosome
•
Onion root tip (top photo), whitefish (bottom
photo)
Mitosis: Anaphase
• The last bit of DNA at the
centromere replicates to
allow the the centromere
to split
• The sister chromatids
separate and are pulled
to opposite sides of the
cell
•
Onion root tip (top photo), whitefish (bottom
photo)
Mitosis: Telophase
• Chromosomes now uncoil
• Nuclear envelope reappears and
surrounds the chromosomes
Cytokinesis
• The cytoplasm and all its contents are
divided between the 2 daughter cells
(cytoplasmic division)
• The red arrow points at the newly
developing plasma (cell) membrane that
creates the 2 new daughter cells
• The 2 daughter cells are exact replicas
of the original parent cell – they are
clones and have the exact same
genetic make-up as the parent cell.
•
Onion root tip (top photo), whitefish (bottom photo)
Can you identify these stages?
A
C
B
D
Answers:
A. Telophase
B. Prophase
C. Cytokinesis
D. Metaphase
C
D
B
A
Can you identify these stages?
Summary
• One parent cell begins the journey through the
cell cycle and 2 new identical daughter cells
emerge from one cycle.
• Mitosis occurs regularly in tissues that require
new cells continuously such as skin cells, hair
follicles, the lining of the digestive tract and in a
newly fertilized egg.
• This process is important as it allows for an
organism to grow and develop over its lifespan
and replenishes dead or dying cells in certain
tissues.
Acknowledgements:
• Images taken from the following sites:
– http://biog-101104.bio.cornell.edu/BioG101_104/tutorials/cell
_division.html
– http://www.accessexcellence.org/AB/GG/mito
sis2.html
– http://www.biology.arizona.edu/cell_bio/tutorial
s/cell_cycle/cells3.html