Stem Cells Flashcards
Potential uses of stem cells in research and medicine?
- To include the repair of damaged tissues
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Stem cells:
An undifferentiated cell characterised by the ability to self-renew by mitosis.
Have the capacity to differentiate into various cell types.
How are undifferentiated cell produced?
- Mitosis
- Meiosis
Mitosis in stem cells:
- Stem cells are able to undergo cell division
- Source of new cells necessary for growth
- Once specialised they lose the ability to divide, entering G0 phase
Why does activity of stem cells need to be controlled?
- Do not divide fast enough then tissues are not efficiently replaced –> aging
- Uncontrolled division form masses of cells called tumours –> cancer
What is stem cell potency:
Ability to differentiate into different cell types.
- The greater the number of cell types they can differentiate into, the greater its potency.
Totipotent
- Stem cells can differentiate into any type of cells.
- Fertilised egg or zygote
- Can differentiate into extra-embryonic tissues (amnion / umbilicus)
Pluripotent:
- Stem cells can form all tissue types but not whole organisms.
- Present in early embryos and are the origin of the different types of tissues within the organism.
Multipotent -
- Can only form a range of cells within a certain type of tissue.
Haematopoietic stem cells
- In bone marrow –> blood cells
- Multipotent
Why have multicellular organisms evolved from unicellular cells?
- Groups of cells working together as one unit can make use of resources more efficiently than single cells operating on their own.
Cambium:
- In the vascular bundle.
- Can differentiate into phloem or xylem cells
Hayflick limit:
- No. times a normal cell will divide in its lifetime
- Telomeres get shorter and cells can’t divide any more
iPSC
Induced pluripotent stem cells
- Re-programmed cells backwards
Why does differentiation take place?
- Specialised to become barriers (skin) or be motile (sperm cells)
- Organs or tissues
- Contain different organelles and have different shapes.
Where are all blood cells derived from?
- Bone marrow
Erythrocytes
Neutrophils
Replacement of Erythrocytes
- Due to lack of nucleus have lifespan of 120 days.
- Stem cell colonies in bone marrow produce 3 billion erythrocytes per kg of body mass per day.
Replacement of Neutrophils
- Essential in immune response
- Live 6 hours
- Replaced by bone marrow colonies in 1.6 billion kg per hour.
- This figure increases during infection.
Embryonic stem cells:
- Present very early stages of embryo development
- After 7 days a mass of cells, blastocyst, forms and cells are pluripotent.
Sources of stem cells in plant cells:
- Meristematic tissue (meristems) (apical meristems - in roots and shoots) –> pluripotent throughout plant life.
- Vascular cambium –> xylem and phloem tissues.
Importance of vascular cambium:
- Vascular bundle tissue grows as the plant grows
Diseases that may be treated via stem cells in future?
- Heart disease
- Type 1 diabetes
- Parkinson’s disease
- Alzheimer’s disease
- Macular degeneration
- Birth defects
- Spinal injuries
Where are stem cells already used?
- Burns (stem cells grown in biodegradable meshes to produce new skin)
- Drug trials (potential new drugs tested on cultures of stem cells)
- Developmental biology (study of changes that occur as multicellular organisms grow)
Ethics
- Embryos donated after fertility treatment.
- Removal of stem cells usually results in the destruction of embryos.
- Religious objections + moral objections. –> murder.
- Embryo’s lack of consensus
Why should embryonic stem cells be used despite the ethical objections?
- Holding back progress that would lead to successful treatment of incurable diseases
- Umbilical cord stem cells are multipotent and not pluripotent.
Gene therapy:
- Severe Combined Immunodeficiency (SCID) are extremely vulnerable to infections and unlikely to life a year.
- Produce no T cells, so B cells can not function. (types of white blood cells)
- Treated with bone marrow transplant –> which depends of finding a matching donor.
Tissue (adult) stem cells:
- Cells present throughout life from birth.
- Found in specific areas such as bone marrow.
- Multipotent –> growing evidence that they can be artificially triggered to become pluripotent.
- Stem cells can be harvested from umbilical cord of babies. –> invasive surgery not needed.
- Can be stored in case individual needs in future. –> stem cells would not be rejected by same person.
Features of stem cells
- pluripotent
- can divide by mitosis
- all genes could be expressed
- undifferentiated
