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Cell Differentiation and
Stem Cells
IB Topics: 2.1.8 – 10
Cell Differentiation
Organisms consisting of a single mass of
cells fused together are multicellular
The cells in these organisms become
specialized for specific functions
Red blood cell carries oxygen, rod cells in the
retina of the eye absorbs light
To carry out their functions, each cell type
develops its own specialized structure
Cell Differentiation
The development of cells in different ways to perform
different functions is called differentiation
This involves each cell type using only some of the genes in its
Every cell contains all the genetic information to carry out every
function, but only a small portion of the genetic material is
When a gene is being used (switched on), we say the
gene is expressed
Gene  make proteins
Cells affect each other; differentiation is determined by
the cell’s position relative to others
Stem Cells
Defined as cells that have the capacity to
self-renew by cell division and to
They are unspecialized cells
Where do we find stem cells?
At an early stage the whole of a human embryo
consists of stem cells, but gradually the cells in
the embryo differentiate
Another source of stem cells … the umbilical
Small numbers of cells seem to remain as stem
cells in adults (bone marrow, skin, and liver)
They give some human tissues considerable powers
of regeneration and repair
Stem cells in other tissues (brain, kidney, and
heart) only allow limited repair
Stem cells vs. “normal” cells
Stem cells are undifferentiated
All or most of their genes can still be
Stem cells are self-sustaining
They can divide and replicate for long periods
of time
Why are we interested?
There has been a great deal of interest in
stem cells because of their potential for
tissue repair and for treating degenerative
MS, Parkinson’s disease, strokes (loss of
Although largely experimental, there is the
potential to use stem cells to repair these cells
Current Research (just some)
Since 1998; a group led by Dr. James
Thompson at the U. of Wisconsin developed a
technique to isolate and grow stem cells
In some countries, stem cell research is
restricted by legal measures
In Denmark, Spain, UK, and Sweden, stem cell
research is allowed using stem cells from
embryos less than 14 days old
In the U.S. in 2006, President Bush vetoed a bill
which would have allowed Federal money to be
used for research where stem cells are derived
from the destruction of embryos
Embryonic vs. adult stem cells
Embryonic stem cells
Adult stem cells
Easier to obtain
No embryo needs to be
Almost unlimited growth
The cells are fully
compatible with the tissues
of the adult so no rejection
Less chance of malignant
tumors developing
Less chance of genetic
damage than with adult
Greater capacity to
differentiate into different cell
Therapeutic use of stem cells
Most therapeutic uses are at a very early
stage of research
Cells that do not work well are replaced
with healthy, functioning cells
Juvenile-onset diabetes and spinal cord
injury are current hot topics
Greatest success so far … bone marrow
transplants (leukemia) and skin grafts for
severe burns
Stem cell animations
Human development and stem cells, mapping
cell fates, creating embryonic stem cell lines,
somatic cell nuclear transfer
Risks and considerations
Stem cells can form tumors called
Develop naturally from stem cells
Ethics … What do you think?