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6
BIO HL S22C
UNDERSTANDING 5
Specialized tissues can develop by cell differentiation in multicellular
organisms.
* what are specialized tissues ?
UNDERSTANDING 5
ROLE OF STEM CELL
Stem cells are defined as cells that have the capacity to divide and to diferentiate along diferent pathways. Human embryos consist entirely of stem cells in their early stages, but gradually the cells in the embryo commit themselvesto a pattern of diferentiation.
STEM CELL
DIFFERENTIATION /
SPECIALIZATION OF CELLS
DIFFERENTIATION
- All diploid cells (autosome) have the same chromosomes so they carry same gene and alleles but not all genes are expressed in all cells
- The cell receives a signal, this signal activates/deactivates genes
- Genes are expressed accordingly, cells are comitted to a certain function
- The cell is specialized
UNDERSTANDING 6
Differentiation involves the expression of
some genes and not others in a cell’s genome
All (diploid) cells share an identical genome
- each cell contains the entire set of genetic instructions
for that organism
UNDERSTANDING 6
BUT not all genes are expressed
as activated in all cells
In (totipotent) embryonic stem
cells the entire
genome is active
EXAMPLE
EXAMPLE
Newly formed cells receive
signals which deactivate
(rarely activate) genes
e.g. a skin cell does
not need to be able to produce haemoglobin
ACTIVE AND INACTIVE GENE
packaged in an
expanded and
accessible form
(euchromatin)
ACTIVE AND INACTIVE GENE
mainly packaged in a condensed form (heterochromatin)
ACTIVE GENE
INACTIVE GENE
CONCLUSION
The fewer active genes in a cell
= the more specialised it will become
As a result of gene expression cell differentiation begins
the cell’s metabolism and shape changes to
carry out a specialised function.
UNDERSTANDING 7
UNDERSTANDING 7
STEM CELLS are unspecialised cells that can:
-Can continuously divide and replicate
-Have the capacity to differentiate into specialised cell types
TOTIPOTENT
Can differentiate into any type of cell.
PLURIPOTENT
Can differentiate into many types of cell.
MULTIPOTENT
Can differentiate into a few closely-related types of cell.
UNIPOTENT
Can regenerate but can only differentiate into their associated cell type
(e.g. liver stem cells can only make liver cells).
Journey Map
STEM CELLS IN THERAPEUTIC USES
The capacity of stem cells to divide and differentiate along
different pathways is necessary in embryonic development
Stargardt's macular dystrophy
Non-Hodgkin lymphoma
LEUKIMIA
APPLICATIONS
STARGARDTS MACULAR DYSTROPHY
- recessive genetic condition (inherited) ABCA4
- 1:10000, children between 6 -12
- an active transport protein on photoreceptor cells to malfunction
- degenerate, hence cannot perform energy transport
- progressive and eventually total loss of central vision
TREATMENT
- embryonic stem cells are treated to divide and differentiate; become retinal cell
USES OF STEM CELLS
- then injected into retina, attaches and becomes functional
-central vision improves, retinal cells becomes more functional
FUTURE
- still in the stage of clinical trial but is more likely to be
used in the future
LEUKEMIA
- cancer of blood or bone marrow
- abnornally high level of poorly functioning white blood cell (above 30,000 per mm3)
TREATMENT
- Hematopoetic Stem Cells (HSCs) are harvested (from bone marrow, peripheral blood or umbilical cord)
- diseased white blood cells are destroyed; chemotherapy and radiation
THERE'S MORE
- new white blood cells need to be replaced
- HSCs are transported back into bone marrow, undergoes
differentiation,
- new healthy white blood cells are formed
APPLICATION 7
ETHICS
Ethics of the therapeutic use of stem cells from specially created embryos ,
from the umbilical cord blood
of a new-born baby
and from an adult’s own tissues
There are some comparions of stem cells between embryo , cord blood and adult
COMPARISONS
comparison 1
comparison 2
THERAPEUTIC CLONING
- cloning designed as therapy for diseases
HOW??
1. cell is inserted into a fertilized egg (removed nucleus)
2. nucleated egg begins to divide, forms blastocyst
3. stem cell is extracted
THERAPEUTIC CLONING
4. the cells is transplanted into the patient to treat the disease
- pave way for future discovories and beneficial technologies
- cure serious diseases or disabilities w cell therapy
- less likely to be rejected (genetically identical)
- x not require death of other human
- stem cells can be taken from embryos that have stopped developing/ would die anyway
- cell taken when embryo have no nervous system
- stemcells created without fertilisation and destrucuton of natural human embryos
ARGUEMENTS FOR
- involves creation and destruction of human embryos
- embryonic stem celss are capable of continued division (can form tumour)
- more embryos are generally produced, excess embryos are killed
- alternative techologies may fulfill similar roles
eg : nuclear reprogramming
- are we creating human life to destroy it (embryo can be used in IVF, develops into human fetus)
- illegal, but not ratified by all nations. first human can be potentially cloned.