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Biology Topic 2 (Using Stem Cells ((Clinical issues, There is no guarantee…
Biology Topic 2
Using Stem Cells
Stem cells can divide to produce new cells, which can then divide into different cell types.
They therefore have the potential to be transplanted into patients to treat medical conditions and disease.
They could be used to replace cells that have been damaged or destroyed, eg:
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in cases of multiple sclerosis, which can lead to paralysis
in cases of spinal cord or brain injury,
that have led to paralysis
Embryonic stem cells can differentiate into a wider range of cell types, but are difficult to obtain. The best source is a five-day-old embryo, although there are clinical, ethical and social issues with their use.
Adult stem cells will differentiate into a narrower range of cell types.
Bone marrow transplants are an example of adult stem cell transplant.
Bone marrow cells will differentiate into different types of blood cell.
Bone marrow transplants are carried out:
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There are clinical, ethical and social issues with their use. These issues will be different for growth and transplant of adult stem cells, embryonic stem cells and therapeutically-cloned stem cells. They will also depend on whether the stem cells are to be used for therapy or research.
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There is no guarantee of how successful
these therapies will be, for example in the use of stem
cells in healing damage caused by Parkinson's disease.
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Mutations have been observed in stem cells cultured
for a number of generations, and some
mutated stem cells have been observed to behave like cancer cells.
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For therapeutic cloning, is it right to create embryos for therapy, and destroy them in the process?
Embryos could come to be viewed as a commodity,
and not as an embryo that could develop into a person.
At what stage of its development should
an embryo be regarded as, and treated as, a person?
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Educating the public about what stem cells can, and can't do, is important.
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Much of the research is being carried out by commercial clinics,
so reported successes are not subject to peer review.
Patients could be exploited by paying for expensive treatments and being given false hope of a cure
as stem cell therapies are only in their developmental stages.
Cell Differentiation
Animals and plants produced by sexual reproduction begin life as a single cell, a fertilised egg or zygote. These cells must divide by mitosis to produce a multicellular organism.
Mitosis happens throughout the bodies of animals but only occurs in specific regions of plants. These are called meristems and are found in the tips of roots and shoots. Here new cells are formed.
Plant cells are also able to become longer as they grow. This process is called cell elongation and occurs throughout the plant, not just in the meristems. Cell elongation does not occur in animals.
The cells of multicellular animals and plants must also differentiate, so that its cells develop features that enable them to fulfil specific roles. Cells that have differentiated have become specialised. Without this specialisation, complex multicellular animals and plants would not exist.
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Excretory system - Remove waste products and unwanted substances. Regulate the water content of the body.
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Nervous system - Respond to internal and external stimuli and conditions. Carry messages for the body to work as a coordinated whole.
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Skeletal system - To bring about movement. Support and protect internal structures. Produce blood cells. Store and release calcium.
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Spongy mesophyll - Allow gases to circulate for the exchange
of gases between the leaf and the environment. Carry out photosynthesis.
Guard cells - Open and close to control the exchange of gases – carbon dioxide, water vapour and oxygen.
Phloem - Sieve tubes Transport products of photosynthesis, including sugars and amino acids, from the leaf to where they are needed.
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Xylem - Xylem vessels Transport water and dissolved minerals from the roots, up the plant.
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Stem Cells
Stem cells are cells that have not undergone differentiation. A cell which has not yet become specialised is called undifferentiated.
An embryo develops from a fertilised egg. Cells at early stages in the development of the embryo are stem cells.
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Some adult stem cells remain in the bodies of adults. These are found in limited numbers at certain locations in the body. Adult stem cells can be found in:blood,brain and bone marrow.
Adult stem cells can differentiate into related cell types only. So bone marrow cells can differentiate into blood cells and cells of the immune system, but not other cell types.
Cell Division
DNA exists in the nucleus as thin strands. When the cells containing nuclei are ready to divide, the DNA copies itself then coils and condenses to form chromosomes.
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Each section of this single molecule of DNA contains a code for the production of a particular protein called a gene.
Each human body cell contains 46 chromosomes. These can be arranged into 23 pairs. Each chromosome in a pair carries the same types of genes.
Cell Cycle
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It is essential that any new cells produced contain genetic information that is identical to the parent cell.
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The first stages of the cell cycle involve cell growth, then synthesis of DNA. The single strand of DNA that makes up each chromosome produces an exact copy of itself. After this a period of further growth occurs and the DNA is checked for errors. Mitosis occurs after this checking has been completed. Finally the cytoplasm of the cell separates and two cells are formed.
Mitosis
The cell undergoes a type of cell division called mitosis. In mitosis, two cells called daughter cells are produced, each identical to the parent cell.
Mitosis is a type of cell division in which a diploid body cell copies itself and finally divides into two identical diploid daughter cells. The daughter cells are clones of each other. Every base pair of their DNA is identical.
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Interphase - The cell spends most of its life in this phase. The DNA in chromosomes copies itself ready for mitosis.
Prophase - The DNA in chromosomes and their copies condenses to become more visible. The membrane around the nucleus disappears.
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Cancer
Cells grow then divide by mitosis only when we need new ones. This is when we're growing or need to replace old or damaged cells.
When a cell becomes cancerous, it begins to grow and divide uncontrollably. New cells are produced even if the body does not need them. A group of cancerous cells produces a growth called a tumour.
Types of tumour
Benign - Grow slowly. Usually grow within a membrane, so can easily be removed. Do not invade other parts of the body.
Malignant Grow quickly. Invade neighbouring tissues and can spread to other parts of the body in the bloodstream. As the tumour grows, cancer cells detach and can form secondary tumours in other parts of the body. This process is called metastasis.
Monitoring Growth
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The growth of babies in all three of these measurements can be monitored using percentile growth charts.
If a baby is born on the 50th percentile for height, then in every hundred babies, 50 will be taller and 50 will be shorter. If a baby is born on the 10th percentile for mass, then in every hundred babies, 90 will be heavier and 10 will be lighter.
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Stem Cells in Plants
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The main meristems are close to the tip of the shoot, and the tip of the root.
Cells of the meristem can differentiate to produce all types of plant cells at any time during the life of the plant.
In a growing shoot, new cells are being produced continuously near the tip. As the cells become older, further away from the tip, they become differentiated. They enlarge and develop a vacuole.
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