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MITOSIS
The Cell Cycle & Mitosis Tutorial
INTERPHASE
• The cell is engaged in
metabolic activity and
performing its prepare for
mitosis (the next four phases
that lead up to and include
nuclear division).
Chromosomes are not clearly
discerned in the nucleus,
although a dark spot called the
nucleolus may be visible. The
cell may contain a pair of
centrioles (or microtubule
organizing centers in plants)
both of which are
organizational sites for
microtubules.
PROPHASE
• Chromatin in the nucleus
begins to condense and
becomes visible in the
light microscope as
chromosomes. The
nucleolus disappears.
Centrioles begin moving
to opposite ends of the
cell and fibers extend
from the centromeres.
Some fibers cross the cell
to form the mitotic
spindle.
PROMETAPHASE
• The nuclear
membrane dissolves,
marking the beginning
of prometaphase.
Proteins attach to the
centromeres creating
the kinetochores.
Microtubules attach at
the kinetochores and
the chromosomes
begin moving.
METAPHASE
• Spindle fibers align the
chromosomes along the
middle of the cell nucleus.
This line is referred to as
the metaphase plate. This
organization helps to
ensure that in the next
phase, when the
chromosomes are
separated, each new
nucleus will receive one
copy of each
chromosome.
ANAPHASE
• The paired chromosomes
separate at the
kinetochores and move to
opposite sides of the cell.
Motion results from a
combination of
kinetochore movement
along the spindle
microtubules and through
the physical interaction of
polar microtubules.
TELOPHASE
• Chromatids arrive at
opposite poles of cell,
and new membranes
form around the daughter
nuclei. The chromosomes
disperse and are no
longer visible under the
light microscope. The
spindle fibers disperse,
and cytokinesis or the
partitioning of the cell
may also begin during
this stage.
CYTOKINESIS
• In animal cells,
cytokinesis results when
a fiber ring composed of
a protein called actin
around the center of the
cell contracts pinching the
cell into two daughter
cells, each with one
nucleus. In plant cells, the
rigid wall requires that a
cell plate be synthesized
between the two daughter
cells.
MITOSIS NOTES
•
•
MITOSIS NOTES
? WHAT DO YOU THINK WOULD HAPPEN IF A CELL WERE SIMPLY
TO SPLIT INTO TWO, WITHOUT ANY ADVANCE PREPARATION?
WOULD EACH DAUGHTER CELL HAVE EVERYTHING IT NEEDED
TO SURVIVE?
NO
CHROMOSOMES
•
•
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–
FRUITFLIES – 8 CHROMOSOMES
HUMANS – 23 CHROMOSOMES
CARROT CELLS – 18 CHROMOSOMES
•
•
•
•
•
•
CHROMATIDS – ONE OF TWO IDENTICAL “SISTER” PARTS OF A
DUPLICATED CHROMOSOME
CENTROMERE – LOCATED NEAR THE MIDDLE OF THE CHROMATIDS,
SOME LIE NEAR THE END
?WHEN ARE CHROMOSOMES VISIBLE?
* DURING CELL DIVISION
? WHY ARE THE SISTER CHROMATIDS IDENTICAL?
* BEFORE CELL DIVISION EACH CHROMOSOME IS DUPLICATED.
THE SISTER CHROMATIDS THEREFORE ARE IDENTICAL
BECAUSE THEY ARE DUPLICATES OF EACH OTHER
THE CELL CYCLE
–
INTERPHASE – PERIOD OF THE CELL CYCLE
BETWEEN CELL DIVISION
CELL CYCLE – THE PERIOD OF TIME FROM THE
BEGINNING OF ONE CELL DIVISION TO THE
BEGINNING OF THE NEXT
DURING THE CELL CYCLE, A CELL GROWS,
PAREPARES FOR DIVISION, AND DIVIDES TO FORM
2 DAUGHTER CELLS, EACH OF WHICH THEN
BEGINS THE CYCLE AGAIN.
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–
•
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FIGURE 10-4 PG. 245 OR WORKSHEET CH. 10 CELL
GROWTH AND DIVISION
MITOSIS – M PHASE – THE DIVISION OF THE CELL
NUCLEUS AND CYTOKINESIS TAKES PLACE
•
S – COPY OF CHROMOSOMES
EVENTS OF THE CELL CYCLE
INTERPHASE IS LONG, THE ACTUAL
CELL DIVISION TAKES PLACE
QUICKLY
• G1 – Cell does what it is supposed to do
• S – Synthesis of DNA
• G2 – Cell prepares for division
– Growth
– Reproduction of cell material, organelles
MITOSIS
–
BIOLOGISTS DIVIDE THE EVENTS INTO 4
PHASES: PROPHASE, METAPHASE,
ANAPHASE, TELOPHASE
•
–
CAN LAST FOR A FEW MINUTES OR UP TO
SEVERAL DAYS
PROPHASE
•
•
•
•
1ST , LONGEST PHASE 50-60%
CHROMOSOMES BECOME VISIBLE
CENTRIOLES – FORM SPINDLE, SEPARATE AND
TAKE UP POSITIONS ON OPPOSITE SIDES OF THE
NUCLEUS
NUCLEOLUS DISAPPEARS AND NUCLEAR
ENVELOPE BREAKS DOWN
PROPHASE
EARLY PROPHASE
LATE PROPHASE
METAPHASE
• CHROMOSOMES LINE
UP ACROSS THE
CENTER OF THE
CELL
ANAPHASE
•
CENTROMERES THAT
JOIN THE SISTER
CHROMATIDS SPLITS,
CAUSING THE SISTER
CHROMATIDS TO
SEPARATE AND
BECOME INDIVIDUAL
CHROMOSOMES. THEY
MOVE TO THE POLES.
ANAPHASE STOPS
WHEN THE
CHROMOSOMES STOP
MOVING.
TELOPHASE
•
CHROMOSOMES
UNCOIL NUCLEAR
ENVELOPE
REAPPEARS
AROUND CLUSTER
OF
CHROMOSOMES.
SPINDLE BEAKS
APART.
NUCELOLUS
REAPPEARS
CYTOKINESIS
•
•
•
USUALLY OCCURS
THE SAME TIME
TELOPHASE
HAPPENS
ANIMAL – PINCHED
INTO NEARLY 2
EQUAL PARTS
PLANT – CELL
PLATE GRADUALLY
DEVELOPS INTO A
SEPARATING
MEMBRANE
DAUGHTER CELLS
ONION ROOT
• Mitosis in Onion Root Tips