Download MITOSIS & CYTOKINESIS

MITOSIS & CYTOKINESIS
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MITOSIS: The nucleus of a cell is divided into 2 nuclei with
the same number & kinds of chromosomes as parent cell.
CYTOKINESIS: The division of the cytoplasm into 2 distinct
cells.
CHROMOSOMES: Contain the genetic information (DNA) passed
on to each generation. They differ in number with ea. Specie.
COMPOSITION OF CHROMATIN: Makes up chromosomes.
Condenses between cell division, chromosomes become visible.
Made up of DNA and proteins. The proteins fold the DNA to
fit into the nucleus. DNA is 10,000 X the length of chromo.
Don & Ada Olins and Christopher Woodcock discovered that
DNA was coiled around histone proteins.
Nucleosomes: Bead-like structures of DNA and histones
These are tightly compacted so they can separate in mitosis.
CHROMOSOMES
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CHROMOSOME STRUCTURE
Chromotids: Identical parts contained in chromosomes (2)
Centromere: Located near the center of chromatids (usually)
CELL CYCLE
A cell grows, prepares for division, and divides to form 2 new
daughter cells.
Mitosis (M phase) Active cell division, nucleus into 2 new ones
Interphase (G1,G2,& S) Period of non cell division, where
other life processes are carried out
Cytokinesis Where the cytoplasm and contents divide
See fig. 8-10
Cells go through the cycle in different rates: muscles vs. skin
INTERPHASE
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http://www.micro.magnet.fsu.edu/micro/gallery.html
INTERPHASE: The period between cell division
G1 (Gap 1): Cellular growth and development takes place
S: (DNA Synthesis): DNA replication takes place,
synthesizing of proteins
G2 (Gap 2): Synthesis of organelles and materials required
for cell division. Shortest of the phases.
Although this phase seems quiet a lot is going on:
synthesizing of mRNA
making of proteins
DNA is copied
ATP is made and utilized
specialized cells do most of their work: secretion, movement
INTERPHASE
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PROPHASE
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PROPHASE
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Longest of the phases taking between 50-60% of total time.
Chromosomes become visible because of coiling of chromotin
Centrioles separate and go to opposite sides of the cell
Centrioles contain tubulin, a microtubule protein
Chromosomes attach to fibers (spindles) near the centromere.
Spindles help move the chromosomes apart and are developed
from the centrioles.
Centrioles are composed of microtubules.
Plant cells do not contain centrioles.
Near the end of the phase coiling becomes tighter, the
nucleolus disappears, and the nuclear envelope breaks down.
METAPHASE
• The shortest of the phases lasting only a few
minutes.
• Chromosomes line up across the center (equator)
of the cell.
• Microtubules connect the centromere of each
chromosome to the poles of the spindle.
• Because of their starlike arrangement around
the poles of the spindle, these microtubules are
called ASTERS.
ANAPHASE
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Begins when the centromeres that joins the sister chromotids
split.
As they separate the spindle grows longer.
The chromosomes move until they have separated into two
groups near the poles of the spindles.
Anaphase ends when the movement of the chromosomes stops.
Force that separates the chromosomes isn’t known.
Microtubule cross-bridging
Microtubule assembly/disassembly
Actinmediated force generation
All have been proposed. Problem is that such a small
force is needed to move a chromosome that pinpointing the
cause is a problem.
ANAPHASE
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TELEPHASE & CYTOKINESIS
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Final stage of mitosis
Chromosomes uncoil into a tangle of chromatin in the regions
where the nuclei of the daughter cells will form.
The nuclear envelope reforms around the chromatin.
Spindles break apart and nucleolus becomes visible.
We now have two nuclei w/ a duplicate set of chromosomes
• CYTOKINESIS
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Division of the cytoplasm into two individual cells
Takes place in a number of ways:
In animal cells the cell membrane moves inward until the
cytoplasm in pinched into two parts w/ their own nucleus etc.
In plants, a cell plate forms midway between the divided
nuclei. It develops into a separate membrane w/ a cell wall.
TELOPHASE
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CYTOKINESIS
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