Download WELCOME TO BIOLOGY 2002 - University of Indianapolis

Mitosis

Mitosis is the process by which new cells are generated.
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Mitosis produces 2 genetically identical daughter cells
Overview of
Mitosis:
Parent cell
Mitosis
Replicated chromosomes
condense at the start of mitosis
Sister chromatids
separate and two
daughter cells are formed.
Parent cell and daughter cell contain the
same complement of chromosomes.
The cell cycle:
Figure 12.5 The stages of mitotic cell division in an animal cell: G2 phase; prophase; prometaphase
Figure 12.5 The stages of mitotic cell division in an animal cell: metaphase; anaphase; telophase and cytokinesis.
Figure 12.5x Mitosis
How do spindle fibers move the chromosomes?
The kinetochore is a specialized region on the
centromere where spindle fibers attach
Motor molecules of the kintochore
walk along the microtubule, taking
the chromosome with it
As the chromosomes move toward
the poles, the microtubules are
broken down at the kinetochore end
Motor molecules "walk" along a microtubule track
Transport
vesicle
ATP
Kinesin
Microtubule
ADP+Pi
ATP
ADP+Pi
After the nucleus divides, cytokinesis divides the
cytoplasm, forming two separate cells
Figure 8.9a
Cytokinesis in animals
Cleavage furrow
Mitosis in a plant cell
Bacteria divide by
binary fission
Bacteria divide by
binary fission
Bacteria divide by
binary fission
Unregulated cell division can lead to cancer

Many factors interact with each other to determine whether a
cell will undergo mitosis

Cell cycle checkpoints normally insure that DNA
replication and mitosis occur only when conditions
are favorable and the process is working correctly.
Cell-Cycle Checkpoints
G2 checkpoint
Pass this checkpoint if:
• cell size is adequate
• chromosome replication is
successfully completed
M
Mitosis
G2
First gap
Metaphase checkpoint
G1
Pass this checkpoint if:
• all chromosomes are
attached to mitotic spindle
G1 checkpoint
S
Pass this checkpoint if:
• cell size is adequate
• nutrient availability is sufficient
• growth factors (signals from
other cells) are present
Cell cycle proteins regulate whether a cell will
proceed past a particular cell cycle checkpoint



cyclin - a protein whose amount varies cyclically
cdk - another cell division control protein - a cyclin
dependent kinase; active only when bound to cyclin
MPF - mitotic promoting factor...
• MPF is a kinase enzyme, ones that switches on/off target
proteins by phosphorylating them.....
• [cyclin + cdk = MPF]...
favors Mitosis
• leads to destruction of cyclin itself
MPF levels rise, causing
the cell to pass through the
G2 checkpoint
Growth factor proteins are signal molecules that trigger a signaltransduction pathway leading to cell division
Platelet-derived
growth factor
Cell division is also
dependent on
environmental factors
Unregulated cell division can lead to cancer

Mutations in genes that encode cell cycle proteins can
lead to unregulated growth, resulting in tumor formation
and ultimately invasion of cancerous cells to other organs.
Cancer cells have escaped cell cycle controls and
divide excessively
Figure 12-17x1 Breast cancer cell
Figure 12-17x2 Mammogram: normal (left) and cancerous (right)
CANCER SPREADS