Transcript Stem cells - KingsfieldBiology

Although all cells contain all genes, only certain
genes are expressed (switched on) in any one
cell at any one time.



E – Describe how stem cell technologies work
C – Analyse data on the subject
A – Evaluate technology and methods



Some genes are permanently switched
on in all cells – can you think of any?
Some genes are permanently switched
off in certain cells e.g. Insulin genes in
the cells lining the small intestine.
Some genes can be switched on and off
when they are needed.
Organisms can develop from a
fertilised egg, known as a
zygote.
 The zygote then starts to
divide, it is symmeterical in its
shape as well as its contents up
to the eight cell stage.
 At this point the cells are said
to be totipotent.
 This means that they are
potentially capable of
expressing all of the genes of
their genome.



At the 8 cell stage if the cells are
separated from each other then the can
grow into a normal individual.
It is a process used to make
twins/triplet/quads etc... (up to
octuplets) in cattle.


The reverse is true as
well, two different eight
cell stage embryos can be
combined and will develop
into a single normal
individual.
Such individuals are known
as chimeras because it
contains cells from
different genetic lines.
The totipotent zygote, which
is capable of producing the
entire organism, will first
divide into pluripotent cells.
 Pluripotent cells that do not
have this ability but can
nevertheless produce all the
tissues of the organism.
 Next will come multipotent
cells, which can produce
various cells within a
particular tissue.
 Last will come specialized
cells.




During the process of specialisation only some
genes are switched on.
This means that only part of the DNA is
translated into proteins, those which are
required to carry out specialised functions.
Though the cell is capable of producing other
proteins it would be wasteful to do so, so the
genes for the proteins are not expressed. This
is done in the following ways:
 Prevention of transcription
 Prevention of translation
In animals – very few, can be for reasons such
as the fact that red blood cells have lost their
nucleus therefore no longer have all of the
genes, others just loose their totipotency.
 A few exists in mature animal cells these are
known as adult stem cells. Can you think where
they are likely to be found?
 In plants many more cells are totipotent (main
exception = xylem for the same reasons as the
red blood cell)
 Under the right conditions many plant cells can
develop into any other cell, this can be the
bases of cloning plants


Using page 237,
explain how plant
growth factors
could be used to
grow a whole
new plant from a
single plant cell

Using the following websites, you books and
your own opinions in pairs/threes produce a
presentation (and I mean a presentation not
just a slide show!) where you explain:
 what stem cell therapy is,
 how it can be used to treat different diseases
 the ethical, legal and social issues surrounding stem
cell therapy.
http://www.bionetonline.org/English/Content/s
c_intro.htm
 http://www.beep.ac.uk/content/345.0.html
 http://www.eurostemcell.org/films
 http://www.hhmi.org/biointeractive/click/inde
x.html
