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LECTURE 8:
MITOSIS AND CYTOKINESIS
INTRODUCTION
1. Cell division is accomplished by
• mitosis = division of chromosomes and
• cytokinesis = division of the cytoplasm
2. Mitosis is the division of somatic cells in
which the appropriate number of
chromosomes is maintained
3. A somatic cell is a body cell of an organism
or a cell that is not involved in reproduction
of a new organism. Somatic cells divide to
recreate themselves
4. Cytokinesis is division of the
cytoplasm to produce two daughter
cells, usually begun during telophase
5. Difference between animals and
plants: plants are divided by the
formation of a cell plate, where animal
cells are divided through the formation
of a cell cleavage. Cell plate materials
originate in the golgi complex.
INTRODUCTION
4.
5.
When the somatic cell has its complete
complement of chromosomes it is said to be in
the diploid condition
At the end of mitosis daughter cells are diploid
Terminology
• Genome : cell’s genetic information
• Somatic : body cells
• Gametes : reproductive cells (sperm and
egg cells)
• Chromosomes : DNA molecules
• Diploid (2n) : 2 sets of chromosomes
• Haploid (1n) : 1 set of chromosomes
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BASIC PRINCIPLE
Cell Division: Key Roles
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Coordination of Mitosis and Cytokinesis
Cell Division
demands
coordination of
DNA replication
(Mitosis) and
division of the
cytoplasm
(Cytokinesis).
Cell Division at
cellular level
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What’s so important about cell
division?
The
process
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The Knit of Identity - Mitosis Precisely and Evenly
Divides Duplicated Chromosomes
interphase
prophase
metaphase
Precisely dividing the duplicated chromosomes has the consequence of
providing each new cell with an identical and complete set of genetic
instructions.
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Mitosis Precisely and Evenly Divides Duplicated Ch
Cytokinesis is the process of cell division and it is distinct and separable
from mitosis.
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In Animal Cells,
a Cleavage
Furrow Forms
and Separates
Daughter Cells
Cleave furrow in a dividing frog10cell.
The Plant Cell Wall Forces Cytokinesis to Play by
Different Rules
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Cancer
• Transformation
• Tumor: benign or malignant
• Metastasis
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Cancer Is One Outcome of A Runaway Cell Cycle
Licentious division - prostate cancer cells during division
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Chromosome and
DNA
What is the difference between DNA and
Chromosome?
What is Karyotype ?
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Cell Devision at
chromosome level
CHROMOSOME
DUPLICATION
AND
SEPERATION
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DNA Replication –
Simple in Principle,
Complicated in Practice
Cell Devision at DNA
level
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DNA is Packaged into Chromosome
duplicated
chromosome
chromatin
DNA in the cell is
virtually always
associated with
proteins.
The packaging is impressive – 2 meters of human DNA fit
into a sphere about 0.000005 meters in diameter.
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The Link Between DNA Replication and Chromosome Du
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DNA is Condensed into Visible Chromosomes
Only For Brief Periods in the Life of a Cell
95% of the time,
chromosomes are like
this.
Easily visible chromosomes
are apparent perhaps 5% of
the time in an actively growing
cell and less in a non-growing
cell.
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A Karyotype is an arranged picture of chromosomes at their
most condensed State
A normal
human
karyotyp
e
Note that almost all chromosomes come in homologous pairs.
Boy or
girl?
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The Cell Cycle
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From Birth to
Rebirth, a Cell
Progresses
Through
Characteristic
Stages That
Constitute the
Cell Cycle
In multicellular
organisms like us,
progress through
the cell cycle is
carefully
regulated.
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The Cell Cycle
1. Interphase (90% of
cycle)
– G1 phase~ growth
– S phase~ synthesis of
DNA
– G2 phase~
preparation for cell
division
2. Mitotic phase
3. Mitosis~ nuclear
division
4. Cytokinesis~
cytoplasm division
INTERPHASE - It is the
time between divisions
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The Cell
Cycle
• G1
• S
• G2
Mitosis &
cytokinesis
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Cell Cycle
regulation
• Growth factors
• Densitydependent
inhibition
• Anchorage
dependence
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Stages of Mitosis
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Mitosis
1.
2.
3.
4.
5.
Prophase
Prometaphase
Metaphase
Anaphase
Telophase
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Mitosis in Action
Blue
shows
DNA,
green
shows
spindle
fibers.
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Stages of mitosis
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Stages of mitosis
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PROPHASE, METAPHASE,
ANAPHASE,TELOPHASE
1. Prophase:
• Chromosomes condense and become visible,
each Chromosome contains several cm of
DNA condensed into 5 – 10 micrometers.
• During the S Phase each chromosome has
been duplicated into a sister chromatid. (A
chromotid is one of the two halves of
duplpicated chromosomes)
S Phase = synthesis of DNA
Prometaphase
• Nuclear membrane
fragments
• Spindle interaction
with chromosomes
• Kinetochore
develops
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2. Metaphase:
1. Chromosomes line up along the cell
“equator”.
2. The cell itself condenses and the
chromosomes are more clearly visible than
during any other phase of mitosis
• Centrosomes at opposite poles
• Centromeres are aligned
• Kinetochores of sister chromatids attached to
microtubules (spindle)
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3. Anaphase
1. is defined as the sister chromatids begin to
separate
2. By now each chromatid is an independent and
functional chromosome
3. The chromosomes are pulled toward opposite
poles. Anaphase is complete when a complete
set of chromosomes reaches each pole.
• Paired centromeres separate; sister chromatids
liberated
• Chromosomes move to opposite poles
• Each pole now has a complete set of
chromosomes
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4. Telophase:
1. The final stage of mitosis, chromosomes
uncoil into chomatin threads
2. A nuclear envelope forms around each set
of chromosomes, nucleoli appear
•
•
•
•
Daughter nuclei form
Nuclear envelopes arise
Chromatin becomes less coiled
Two new nuclei complete mitosis
Structure of a replicated
chromosome
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Counting chromosomes and
chromatids
• n = haploid number of chromosomes
– Example: the humans have 23 different
chromosomes (n=23).
– Diploid cells have 2n chromosome #.
Human diploid cells, have 46
chromosomes (2n=46).
• c = number of chromatids in
unreplicated (G1) haploid state.
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Replication of a
chromosome during mitosis
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CONTROLS ON DIVISION
1. Frequency of mitosis varies between
species or even with location within an
organism…skin cell versus nerve cells for
example, but under similar conditions the
length of the cell cycle is constant for a
particular type of cell.
2. The rate and frequency of mitosis in a
multicelluar organism must be controlled…
3. The cell requires a protein called maturation
promoting factor (MPF). Scientists are still
learning how MPF works and controls the
cell mitosis.
• Read about the effects of Colchicine
and the condition of polypoidy
• When mitosis occurs each daughter
cell receives exactly the same number
and kind of chromosomes as the parent
• When a haploid cell undergoes mitosis,
two haploid cells are produced.
The End