Cell division
How one cell becomes two
Mitosis + Cytokinesis = Cell division
• Most cells in all eukaryotic organisms will divide
many times throughout the life of the organism
– Mitosis is the process by which a cell duplicates its
genetic materials (chromosomes and prepares for
cell division
– Cytokinesis is the division of the rest of the cell into
two different daughter cells
– Prokaryotes also divide through binary fission, but this
is NOT mitosis/cytokinesis
• In animals, cell division occurs during embryonic
development, growth, and wound healing
• Errors during cell division can cause cell death
or cancer
Mitosis reorganizes DNA in the cell
• Prior to mitosis, the cell creates an exact
duplicate of its DNA material
• During mitosis, the two copies are reorganized,
repackaged into two sets of chromosomes, and
divided to opposite ends of the cell
• In most organisms, mitosis is immediately
followed by cytokinesis (the cell body dividing in
two)
• The original cell (mother cell) is identical to the
two resulting cells (daughter cells)
Mitosis vocabulary
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Nucleus – location of DNA inside the cell
Nuclear envelope – the membrane that separates the nucleus from the cytoplasm
DNA – an incredibly long molecule that contains genetic blue prints for cell behavior
Chromatin – a loosely bundled coil of DNA. Most of the time, DNA is organized in
this form, “ a loose rope”
Histones – proteins which hold a DNA strand together in the form of chromatin
Chromosome – a highly organized form of chromatin, “a tightly wrapped and carefully
knotted rope ”
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Each chromosome is composed of two identical parts called chromatids
Chromatids: two halves of a chromosome which contain the same genetic information
DNA exists in the form of chromosomes only during mitosis
Each chromosome looks like an X
Centromere – a bundle of proteins which connects the two chromatids of a
chromosome, the “knot at the center of the X“
Microtubules – part of a cell’s cytoskeleton. These are tubes of protein which use to
pull chromosomes apart and to opposite ends of a cell during mitosis. They are
powered by ATP!
Mitotic spindle – How microtubules are organized during mitosis. This is a collection
of microtubule fibers which is formed to coordinate the pulling of apart of
chromosomes.
Metaphase plate – the line along which chromosomes are lined up during mitosis.
This arrangement is coordinated by the mitotic spindle.
Chromosome Structure
5 Phases of Mitosis
• Mitosis is composed of five phases
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Prophase
Prometaphase
Metaphase
Anaphase
Telophase
• During each phase, different proteins in the cell
perform specific roles to divide the two copies of
genetic material
• Cytokinesis occurs after mitosis to create two cells
Prophase
• Chromatin is being organized
into chromosomes inside the
nucleus
• Microtubules are organized
into mitotic spindles in the
cytoplasm
• Nuclear envelope is dissolving
• By the end of prophase
– Chromosomes and mitotic
spindle are fully organized
– Nuclear envelope has
disappeared
Prometaphase
• Chromosomes move towards
each other and into the
center of the cell
• Microtubules move into the
nuclear region and begin to
connect to chromosomes at
the centromere
• Microtubules organize into
two mitotic spindles, one at
each end of the cell
Metaphase
• The mitotic spindle is
fully organized, and
has pulling the
chromosomes to the
center of the cell
• The spindle aligns
chromosomes so that
each centromere is
lined up along the
metaphase plate (the
center of the cell)
Anaphase
• Each chromosome is
pulled apart into two
chromatids (halves) at the
centromere
• Microtubule fibers contract
(using ATP!), pulling
chromatids to opposite
ends of the cell towards
the two spindles
Telophase
• Chromatids arrive at opposite
ends of the cell and begin to
unfold into loose coils of
chromatin
• New nuclear envelopes begin
to form around the chromatin to
create two nuclei
• Spindle fibers disperse into the
cytoplasm
• The cell membrane begins to
cleave in preparation for
cytokinesis
Cytokinesis
• The cell membrane is being pinched off to
form two separate compartments
• Cytoplasm and organelles are being
divided between the two forming cells
• At the end of cytokinesis, the membrane
fuses to create two daughter cells which
contain identical copies of DNA, and equal
amounts of cytoplasm and organelles
• Cell division is complete!
Cell division movies
• http://www.youtube.com/watch?v=VlN7K19QB0
• http://www.youtube.com/watch?v=CzPGh
YiGyZ8&feature=related
• Embryonic division in the worm c.elegans:
http://www.youtube.com/watch?v=zsgOl04
PESI&NR=1
• http://www.cellsalive.com/mitosis.htm