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CHAPTER 8
MITOSIS
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MITOSIS

Cell division is essential to:
Replace dead cells (50 million cells die per
second)
Repair damaged tissues
Growth
Maintain the body

Cell division includes two main events:
Mitosis – division of nucleus and DNA
Cytokinesis – division of the cytoplasm and
organelles
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THE CELL CYCLE
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Most cells go through the same cell cycle
Time at each stage varies
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5 stages to life cycle of a cell, but is a
continuous process
The five stages are:

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G1—gap (growth) phase one
S—synthesis
G2—gap (growth) phase two
Cell division (mitosis and cytokinesis)
G0—gap (growth) mitotic dormancy
THE CELL CYCLE
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THE CELL CYCLE

G0 phase – cells are not dividing, they are
differentiated or specialized in their
function
Some cells remain in the G0 phase (nerve
cells)
Others can proceed back into the growth
cycle (G1 , S, and G2) – bone cells

G1 , S, and G2 , occur during the stage
called interphase.
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THE CELL CYCLE
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G1 phase – cell growth, manufacture of tRNA,
mRNA, ribosomes, enzymes, other cell
components
S phase – a new DNA strand is synthesized
G2 phase – the cell prepares to go through
mitosis
During interphase, cells are engaging in various
metabolic activities such as:
 Photosynthesis
 muscle cell contractions
 glandular-cell secretion
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A CELL DURING INTERPHASE
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After interphase, the chromosomes consist of two
strands known as sister chromatids
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STAGES OF MITOSIS
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The stages of mitosis are:
Prophase
Metaphase
Anaphase
Telophase
PROPHASE

First stage of mitosis
Individual chromosomes become visible.
Nuclear membrane begins to disappear.
Spindles begin to form.
Two identical chromatids are attached by
the centromere.
Centrioles move to opposite poles.
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A CELL DURING EARLY
PROPHASE
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A CELL DURING LATE
PROPHASE
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METAPHASE
 Second
stage of mitosis
Nuclear membrane has disappeared
Centrioles are at opposite poles
Chromosomes are aligned at equatorial
plane (middle of cell)
Each chromosome still has two chromatids
human cells have 46 chromosomes, each with
two chromatids (total of 92 chromatids)
Chromosomes are attached to the spindle
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A CELL DURING METAPHASE
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ANAPHASE

Third stage of mitosis
Centromeres split and chromatids
(daughter chromosomes) separate
Chromatids are pulled to opposite poles
by the spindle which attaches to a
protein (kinetochore) at the centromere
Each chromatid is the exact copy of the
other
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A CELL DURING ANAPHASE
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TELOPHASE

Last stage of mitosis
Cytokinesis (division of the cytoplasm) takes
place
Chromosomes unwind
Nuclear membrane reappears enclosing the
chromosomes
Nucleoli reappear
Each daughter cell now enters G1 stage of
interphase
Cells grow and enter another cycle of mitosis.
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TELOPHASE/CYTOKINESIS
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MITOSIS
IN
ANIMAL
CELLS
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PLANT AND ANIMAL CELL
DIFFERENCES

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Animal and plant cells have very similar cell
division cycles
Differences include:
Plant cells do not have centrioles, but
are still capable of producing a spindle
During cytokinesis, animal cells form a
cleavage furrow, plant cells form a cell
plate which becomes the cell wall.
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MPARISON OF ANIMAL AND PLANT MITOS
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COMPARISON OF ANIMAL AND
PLANT MITOSIS
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PLANT AND ANIMAL CELL DIFFERENCES
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DIFFERENTIATION

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Even though all cells originate from a single
fertilized egg, they are not the same
All cells are genetically identical but have
different functions
 nerve cells
 muscle cells
 red blood cells . . . each with a specific function

The process of creating these specialized cells
is called cell differentiation
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STEM CELLS
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Cells that can become any cell type
Stem cells in the bone marrow can be
differentiated and become a red or white
blood cell
Bone marrow transplants are successful for
treating certain diseases because the stem
cells can differentiate to the desired cells
Other sources include embryonic stems
cells and umbilical cord stem cells
Both sources could potentially be used to
produce nerve, liver, muscle, skin, or brain cells
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ABNORMAL CELL DIVISION
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Cells that have lost their ability to stop dividing are
known as cancerous cells or tumors.
 Benign tumor – stays in one location
 Malignant tumor – can spread and invade other parts of
the body

Uncontrolled cell division in white blood cells causes
leukemia.
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Cancer can be caused by carcinogens.
Some cancers can be treated through surgery.
Other treatments include chemotherapy and
radiation.
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ABNORMAL CELL DIVISION

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Chemotherapy uses a combination of chemicals to
destroy cancer cells.
Side effects include susceptibility to infections, hair
loss, and intestinal disorders
Radiation uses X rays or gamma rays that disrupt
the DNA structure of cancer cells
Causes the cells to commit “suicide” (apoptosis)
Side effects include hair loss, bloody vomiting and
diarrhea, reduced white blood cell count
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CHAPTER 8
MITOSIS
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After interphase, the chromosomes consist of two
strands known as sister chromatids
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MITOSIS
IN
ANIMAL
CELLS
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MPARISON OF ANIMAL AND PLANT MITOS
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PLANT AND ANIMAL CELL DIFFERENCES
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