Transcript Mitosis and Meiosis - Ms. Petrauskas' Class

Mitosis
Cell division
Agenda
Cell cycle
Mitosis Overview
When things go wrong
The Expectations
2.5.1 Outline the stages in the cell cycle,
including interphase (G1, S, G2), mitosis and
cytokinesis
The Cell Cycle…
• Cells have a life cycle, called the cell cycle
• The cell cycle consists of 3 stages:
– Interphase (growth and replication)
– Mitosis (Nuclear(DNA) division)
– Cytokinesis (cytoplasm division)
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
• 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.aDNA 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. This is doubled to 92 strands (still
considered 46 chrom) during the S stage of interphase.
Mitosis and Cytokinesis
• Mitosis(M phase) –refers to the process of
nuclear division. Results in two identical
nuclei.
• Cytokinesis (C phase)- occurs after mitosis and
is the actual physical division of the cell. Not
included in mitosis
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 Basics: Genetic Material
DNA
• Deoxyribonucleic Acid (DNA): Double helix
strand containing genetic code that acts as
instructions for the cell
• Chromatin structurally loose DNA in the cell
during interphase.
• Chromosome: DNA and associated proteins
(nucleosomes/histones) that help condense
chromosome into a smaller area during mitosis.
• Histone: Proteins that DNA wraps around to
become condensed chromosomes
Chromosomes
one chromosome
(unduplicated)
Chromosome: a long
piece of supercoiled 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
Mitosis Structures
• Centromeres: A centromere is a region on a
chromosome that joins two sister chromatids.
• Centrioles: a cylindrical cell structure
composed mainly of a protein called tubulin.
Produce spindle fibres.
• Mitotic spindle: microtubule-based bipolar
strands that segregate the chromosomes in
mitosis
Cyclins
• Cyclins are involved in the control of the cell
cycle
• Cyclins bind to enzymes called cyclindependent kinases. These kinases become
active and attach phosphate groups to the
proteins in the cell. The attachment then
triggers other proteins to become active and
carry out their various functions.
•
•
•
•
Cyclin D triggers cells to move from G phase to S phase
Cyclin E prepares the cell for DNA replication in S phase
Cyclin A activates DNA replication inside the nucleus
Cyclin B promotes the assembly of the mitotic spindle
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.
Mitotic Index
• Mitotic index= number of cells in mitosis
total number of cells
Useful prognostic
tool for predicting
response of cancer
cells to
chemotherapy
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
metaphase plate
*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 becomes 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
Mitosis Summary
Two divisions occur during cell division
• Nuclear division (mitosis) and cytoplasmic division (cytokinesis)
During interphase genetic material is replicated
2 Identical daughter cells produced
Embryonic growth is a result of repeated mitotic divisions
• A zygote is one cell after fertilization. As divisions occur, specialization
occurs.
Cancer
• There is a strong correlation between smoking
and cancer
• Women smokers are 25.7 times more likely than
women who never smoked to develop lung
cancer. For men smokers, it’s 25 times the risk of
men who never smoked. (Source: US Surgeon
General Report 2014)
• Besides lung cancer, tobacco use also increases
the risk for cancers of the mouth, lips, nose and
sinuses, larynx (voice box), pharynx (throat),
esophagus (swallowing tube), stomach, pancreas,
kidney, bladder, uterus, cervix, colon/rectum,
ovary (mucinous), and acute myeloid leukemia.
(Source: Cancer Facts & Figures 2014)
Cancer
• Mitosis and cell division are under strict
control. Only producing cells when needed for
growth and repair
• Mutagens, oncogenes and metastasis are
involved in the development of primary and
secondary tumors
• Tumour repressive genes- inhibit cell division
• Prot-oncogenes- stimulate growth/division
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
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
Any Questions?