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Summary Notes on Stem Cells - AQA A Level Biology
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Stem cells – AQA A Level Biology Summary NotesPotency = the range of different types of cell it can become
Number of different kinds of potency:
1. totipotent (zygote) - can become every type of cell, including cells that will become
the placenta - 1 cell
2. pluripotent (embryo) - can become every type of cell, except cells that will become
the placenta - treat human disorders due to ability to divide an unlimited number of
times and almost any type of cell
3. multipotent (adult stem cells) - can become a few different types of cell
4. unipotent (most body cells) - can only become 1 type of cell eg skin cells become
more skin cells, muscle cells become more muscle cells - NOT STEM CELLS
Totipotent cells
can divide to replace themselves and differentiate to specialise into any type of body
cell
during development, totipotent cells translate only part of their DNA, resulting in
specialisation
specialisation is a gradual and irreversible process in most animal cells - more
specialised cells = harder to form other types of cell
only occur for limited time in mammalian embryos
Mature plants contain totipotent cells - explains why cloning is so easy! take small group of
plant cells, culture them to produce an unspecialised callus which will divide and
differentiate into genetically identical individuals
Changes in gene expression which determine the fate of unspecialised cells is determined
by:
extrinsic factors eg temp and small molecules from environment
intrinsic factors eg detection of signalling molecules eg growth factors,
morphogenetic and cytokines
STEM CELLS - unspecialised cells that can divide to replace themselves and different into
other cells
3 main categories of stem cells
1. Embryonic Stem Cells (toti or pluripotent)
2. Adult Stem Cells (multipotent)
3. Induced Pluripotent Stem Cells (iPS)
1. Embryonic stem cells (cells in embryo)
collected from unwanted IVF embryos
pluripotent - can make every type of cell, expect placenta
1. Adult Stem Cells
found in bone marrow
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