2.1.6 Cell cycle - Stem cells Flashcards
What are undifferentiated cells called?
Stem cells
Stem cells are able to undergo cell division again and again, and are the source of new cells necessary for growth, development, and tissue repair.
Why does the activity of stem cells need to be strictly controlled?
If they do not divide fast enough then tissues are not efficiently replaced, leading to ageing. However, if there is uncontrolled division then they form masses of cells called tumours, which can lead to the development of cancer.
Define Potency
A stem cell’s ability to differentiate into different cell types
The greater the number of cell types it can differentiate into, the greater its potency.
Define Totipotent
These stem cells can differentiate into any type of cell.
Define Pluripotent
These stem cells can form all tissue types but not whole organisms. They are present in early embryos and are the origin of the different types of tissues within an organism.
Define Multipotent
These stem cells can only form a range of cells within a certain type of tissue. Haematopoietic stem cells in bone marrow are multipotent because this gives rise to the various types of blood cell.
What are the sources of animal stem cells?
Embryonic stem cells – these cells are present at a very early stage of embryo development and are totipotent. After about 7 days a mass of cells, called a blastocyst, has formed and the cells are now in a pluripotent state. They remain in this state in the fetus until birth.
Tissue (adult) stem cells – these cells are present throughout life from birth. They are found in specific areas such as bone marrow. They are multipotent, although there is growing evidence that they can be artificially triggered to become pluripotent.
What are the sources of plant stem cells?
Stem cells are present in meristematic tissue (meristems) in plants.
Where is meristematic tissue found?
In the apex of roots and tips, in the bud, and in cambium.
Meristematic tissue is also located sandwiched between the phloem and xylem tissue and this called the vascular cambium.
What are the uses of stem cells?
Stem cells transplanted into specific area have the potential to treat certain diseases, such as:
- Heart disease
- Type 1 diabetes
- Parkinson’s disease – the symptoms (shaking and rigidity) are caused by the death of dopamine-producing cells in the brain; drugs currently only delay the progress of the disease.
- Alzheimer’s disease – brain cells are destroyed as a result of the build up of abnormal proteins; drugs currently only alleviate the symptoms
- Macular degeneration – this condition is responsible for causing blindness in the elderly and diabetics; scientists are currently researching the use of stem cells in its treatment and early results are encouraging.
- Birth defects
- Spinal injuries
Stem cells are already used in such diverse areas such as:
- The treatment if burns – stem cells grown on biodegradable meshes can produce new skin for burn patients, this is quicker than the normal process of taking a graft from another part of the body.
- Drug trials – potential new drugs can be tested on cultures of stem cells before being tested on animals and humans.
- Development biology – with their ability to divide indefinitely and differentiate into almost any cell within an organism, stem cells have become an important area of study in development biology.
This is the study of the changes that occur as multicellular organisms grow and develop from a single cell, such as a fertilised egg (and why things sometimes go wrong).
Ethics?
The removal of stem cells from embryos normally results in the destruction of the embryos, although techniques are being developed that will allow stem cells to be removed without damage to embryos.
There are not only religious objections to the use of embryos in this way but moral objections too – many people believe that life begins at conception and the destruction of embryos is, therefore, murder. There is a lack of consensus as to when the embryo itself has rights, and also who owns the genetic material that is being used for research.
The use of plant stem cells does not raise the same ethical issues as animal cells.
