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Mitosis
Cell division
Agenda
Cell cycle
Mitosis Overview
When things go wrong
The Basics: Genetic Material
Chromatin in the cell during
interphase is structurally loose
DNA
• Chromosome: DNA and associated proteins
(nucleosomes/histones) that help condense
chromosome into a smaller area during
mitosis.
Chromosomes
one chromosome
(unduplicated)
Chromosome: a long
piece of coiled DNA and
proteins. The number of
chromosome in each
organism differs. 46 in
humans. Seen only when
the cell divides.
Sister chromatids: 2
identical copies of the
same chromosome
one chromosome
(duplicated)
Centromere
Sister Chromatids
Cell theory
• All living things are made of cells
• Cells are the basic unit of life
• All cells come from pre-existing cells
– Cell division is how life is perpetuated
– Humans start out a s a single cell
Why Divide?
It is because the Surface area of a cell to its
cytoplasm volume ratio affects the exchange of
materials and wastes through the cell.
Why do cells divide?
1. If cells got too large, they would not be able
to carry out their functions to survive
2. Growth: allow organisms to grow from a
single cell to a multi-celled organism
3. Maintenance: allows new cells to replace
worn-out or dead cells
4. Repair: regenerates damaged tissues
The Cell Cycle…
• Cells have a life cycle, called the cell cycle
• The sequence of events from one division to
the next.
• Cell division is a very small part of a cells life.
• The cell cycle consists of 3 stages:
– Interphase (growth and replication)
– Mitosis (Nuclear(DNA) division)
– Cytokinesis (cytoplasm division)
Stages of Cell Cycle
• Mitosis(M phase) –refers to the process of
nuclear division
• Cytokinesis (C phase)- occurs after mitosis and
is the actual physical division of the cell. Not
included in mitosis
• Interphase: (G1, S, G2)
The Cell Cycle
G1
Synthesis of DNA
for Duplication of
chromosomes
Phase of rapid
cell growth
S
Growth and
preparation for
cell division
G2
M
Interphase
•
•
•
•
Most of the time of a cell’s life
The stage between mitotic divisions
Made of G1, S and G2 phase
The cell grows takes in nutrients and produce
proteins which are used for energy, growth and
repair
• After a period of rapid growth (G1), the cell
prepares for division by duplicating its
chromosomes within the nucleus (S phase)
• After duplication there is another growth period.
The cell ensures there is enough of everything for
the division.
Interphase
• 1. Stage G1: primary growth phase. Increase
in proteins and in the number of cell
organelles.
• 2. Stage S: indicates the synthesis of DNA.
A.k.a- DNA replication
• 3. Stage G2: Chromosome condensation,
preparation for mitosis.
• Longest stage of cell cycle (The part where it does not
divide). (G1, S, G2). Human cells contain 46 chromosomes
during the G1 stage of interphase.
The Expectations
Describe the events that occur in the four
phases of mitosis
-PMAT-
Prophase
*chromatin condenses into
chromosomes that contains 2
sister chromatids attached by
a centromere
* Centrioles move
to poles
*the
nuclear envelope and
nucleolus disintegrate
*Mitotic spindle forms from
microtubules
*the pair of sister chromatids
attach to the spindle at their
* Sister chromatids
centromeres.
present
*in animal cells, a pair of
centrioles move to each end,
called the poles
* During late prophase the nuclear envelope breaks down and each
chromosome is connected to a spindle fibre by its centromere
Metaphase
*Each chromosome
becomes completely
condensed. The
chromosomes line up at
the centre of the cell.
Line up at the equitorial
plate (equator)
*The mitotic spindle
(made of tubes) is
complete and extend
from each pole
(centrioles) to the
middle of the cell.
Anaphase
• The sister chromatids separate at the
centromere. Each is now called a chromosome.
The separated chromosome are pulled to
opposite poles by the spindle fibres
Telophase
•
•
•
•
•
•
Chromosomes have arrived at the poles
Spindle disappears
Centrioles replicate (in animals)
Nuclear membrane reappears
Nucleolus beocmes visible
Chromosomes become chromatin
Cytokinesis
• The cell divides the cytoplasm and organelles into
two portions (splitting known as cytokinesis)
• The cell membrane cleaves inward and in plant
cells a cell plate forms, nuclear membrane
reforms and spindle disappears
• 2 identical daughter cells result
Mitosis is an Animal cell
Metaphase
Anaphase
Chromosomes line upThe centromeres divide and
the resulting chromosomes,
at the equatorial plate.
Chromosomes continue
move to opposite poles of the
The nuclear membrane
to condense.
Early Prophase
completely dissolves.cell. An identical set
The centrioles assemble
(homologues) of chromosomes
and spindle
moves to each pole.
attach to the
The chromosomesfibres
condense,
becoming shorter centromeres
and thicker. of
thetochromosomes.
The
The centrioles move
opposite
nuclear
membrane
poles of the cell and
spindle
starts to dissolve.
fibres start to form.
Telophase
DNA replicated and cell
Chromosomes lengthen again,
prepares for division. In
the spindle fibres dissolve,
and a
Interphase
humans, 46 chromosomes
nuclear membrane forms around
are duplicated (46 pairs).
Telophase
the chromosomes. In humans,
Late Prophase
Interphase
each new nucleus contains 46
unique chromosomes
http://www.youtube.com/watch?v=AhgRhXl7
Difference between Plant and Animal
Cell Division
Differences in Cell Division Between Animal Cells & Plant Cells
Animal Cells
Plant Cells
Late in anaphase, the plasma membrane pulls
After anaphase, a new cell wall
inward forming a cleavage furrow, which
forms between the two new nuclei
divides the cell in two during telophase.
to create two cells.
No centrioles are found in plant
A centriole is found at each pole during mitosis.
cells.
Uses of Mitosis in Eukaryotic Cells:
a. during growth of the individual.
b. when tissues have been damaged and need to be repaired (as in healing of a cut).
c. to reproduce asexually.
Mitosis Summary
Two divisions occur during cell division
• Nuclear division (mitosis) and cytoplasmic division (cytokinesis)
During interphase genetic material is replicated
During G1 there are 46 single stranded chromosomes and then after the S phase there are 46
double stranded chromosomes
2 Identical daughter cells produced
Both daughter cells are diploid 2n=46
Embryonic growth is a result of repeated mitotic divisions
• A zygote is one cell after fertilization. As divisions occur, specialization occurs.
Cell Death
• Apoptosis: regulated or controlled cell death
of cells that are no longer useful. This is also
used to control cells that have stopped
performing properly
– E.g your body must produces cells to fight a viral
infection. When the infection is gone the cells are
removed by apoptosis
Cancer
• Cancer: Disorder in which some of the body's
cells lose the ability to control their growth.
• Tumour - repeated, uncontrolled cell division to
form a mass of cells. This can happen in any
organ. Some tumours grow large and spread to
other parts of the body (metastasis). The diseases
caused by the growth of tumours is known as
cancer.
– Tumours can be benign (harmless) or malignant
(spread)
Causes
• Carcinogens (increase chances of mutation
leading to cancer)
– Radiation (gamma, UV, x-ray etc.)
– Chemicals (textile dyes, paints and inks)
– Viruses (hepititis B and C and HPV)
Removal
• Surgical– physically excise the tumour cells
• Radiation– using strong ionising or nuclear radiation beam which
can be directed to a point and burn the cells
• Chemotherapy– Uses chemicals to destroy all rapidly dividing cells by
medication. Can destroy other rapidly dividing cells
(hair, stomach/intestinal cells, sperm)
Cancer vs. Normal cells
Cancer cells
Normal Cells
Make exact copies of
themselves during mitosis
Make exact copies of
themselves during mitosis
Do not stop reproducing
Behave independently
Reproduce 50-60 cells
Work dependently/stick
together
Self destruct “apoptosis”
when old
Metstacize, no controlled
death
Any Questions?