Transcript Stem Cells and Cell Differentiation

CELL DIFFERENTIATION (SPECIALIZATION)
Textbook Reference: pg. 38-45
THE SAME …. BUT DIFFERENT
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Mitosis produces cells with exact copies of the same
chromosomes…therefore the same genes
But cells will produce different proteins and therefore
differ in structure and function
E.g. Bone cells, nerve cells, muscle cells, skin cells….
AND IT ALL BEGINS WITH ONE CELL!
Every new organism (animal or plant) begins as
a single cell, the fusion of their parents genes
(sperm + egg = zygote)
 This cell divides into two identical cells by the
processes of mitosis and cytokinesis.
 Two daughter cells then divide and the process
continues.
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Blastocyst
Every cell contains the same chromosomes and
the same genes.
 How then do organisms produce very different
types of cells?
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Not every gene in a cell gets expressed or
“switched on”.
 Therefore, not every protein gets produced!
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FACTORS THAT AFFECT CELL SPECIALIAZTION
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What decides how/which genes are expressed?
Cytoplasm in the Cell – amount of cytoplasm
and number of other organelles affects how the
cell will develop
2. Environmental Conditions of the Cell –
temperature, nutrients, contaminants….
3. Neighbouring Cells – diffusion across the cell
membranes from one cell to another when cells
are close to each other (chemical
communication between cells)
1.
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Both plants and animals have cells which can
become ANY type of cell
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Plants – meristematic cells
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Animals – embryonic stem cells
ANIMALS - STEM CELLS
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Unspecialized cells – the first few cells within an
embryo are totipotent - able to eventually become any
type of cell
As an embryo develops (after 1 week), cells become
less versatile and can only produce some kinds of
cell (tissue). They are pluripotent.
After birth, people have only adult stem cells (or
unipotent)– these can only produce very specific
types of cell. E.g. Skin cells can only produce more
skin cells.
STEM CELL RESEARCH AND USES
Embryonic stem cells – can be cultured (grown)
to produce many types of tissue
 Holds great promise for treating many diseases
including life-threatening ones. Many would say
that this fact alone should mean “full speed
ahead” with research.
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ETHICAL ISSUES
Requires the destruction of an embryo - usually
grown from eggs fertilized with sperm “in vitro”
(outside the womb)
 Some say this is destroying a human life (a
person)
 Some say that personhood does not come until
much later (brain cells?, blood?)
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Adult stem cells – can be cultured (grown) to
produce the type of tissue they came from
 No ethical issue
 Requires the addition of “growth factors”
(nutrients)
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CANADA – FIRST LAWS IN 2002
Embryos can only be used which are no longer
wanted for reproductive purposes.
 Illegal to “create” embryos solely for stem cell
research
 Embryos must be less than 14 days old (after
conception) to be used to harvest stem cells
 Donors must provide consent to the use of
embryos
 Cannot buy/sell embryos
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ALTERNATIVE - INDUCED PLURIPOTENCY
Very recent research (last 5 years)
 Taking normal tissue cells (e.g. skin) that are
unipotent and “forcing” them to become
pluripotent (by the addition of genes)
 A kind of “cellular reprogramming”
 This removes the ethical issue (no destruction
of embryos/blastocysts)
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TISSUE ENGINEERING
(GROWING ORGANS IN THE LAB)
http://singularityhub.com/2009/06/08/growing-organs-in-the-lab/
Human skin grown in the
lab from stem cells
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http://www.youtube.com/watch?v=4nqw1yjyK
Es&safety_mode=true&persist_safety_mode=1
&safe=active