Stem Cells Flashcards
What are stem cells
A stem cell is an unspecialized cell from the embryo, fetus or adult.
What are some features of stem cell
- Under certain conditions, have self-renewal capability by reproducing itself for longer periods or, in the case of adult stem cells, throughout the life of the organism
- Can differentiate whereby unspecialized cells give rise to specialized cells that make up the tissue and organs of the body
- possess large nuclear to cytoplasmic ratio
What can stem cells do due to their unique features
- able to replenish their own population
- generate cells that travel down different differentiation/developmental pathways
Name the first general property of stem cells
- fundamental property of stem cells is that is does not have any tissue-specific structures that allow it to perform specialized functions
Name the second general property of stem cells
- Unlike muscle cells, blood cells or nerve cells (which do not normally replicate themselves) stem cells may replicate many times (a process called proliferation)
- If resulting cells continue to be unspecialized like the parent stem cells, the cells are said to be capable of long-term self renewal by mitotic divisons
Name the third general property of stem cells
- When unspecialized stem cells give rise to specialized cells, the process is called differentiation. Signals inside and outside cells trigger stem cell differentiation.
What are the internal signals that trigger differentiation
- During differentiation, differential gene expression occurs when certain genes become activated and other genes become inactivated in an intricately regulated fashion.
- As a result a differentiated cell develops specific structures and performs certain functions
What are the external signals triggering differentiation
- chemicals secreted by other cells
- physical contact with neighboring cells
- certain molecules in the microenvironment
What are totipotent stem cells
- they are called master cells of the body as they have the ability to give rise to all cell types that make up an organism (even cells of the extra-embryonic membranes like placenta)
- They consist only of zygotic stem cells
When are totipotent stem cells formed
- Occur at the earliest stage of embryonic development ; before the blastocyst stage
- They exists as the fertilised egg (zygote) divides rapidly by mitosis to form a compact ball of cells called morula
What are pluripotent cells
- Cells descended from totipotent stem cells. Have the ability to give rise to types of cells that develop from the three germ layers (mesoderm, endoderm and ectoderm) from which all cells of the body arise.
- Do not have the potential to make differentiated cells that form the extra-embryonic membrane (placenta)
- Embryonic stem cells (ESC) are examples of pluripotent cells
What are the sources of human pluripotent stem cells
- Inner cell mass of early human embryos and fetal tissue that was destined to be part of the gonads
What are multipotent stem cells
- Cells descended from pluripotent stem cells and can differentiate into many cell lines within a specific type of tissue. Adult stem cells are examples.
- They are more specialized than totipotent and pluripotent stem cells, and can only differentiate into a limited number of cell types.
Advantages of embryonic stem cells for scientists
- can become most cells of the body
- easier to culture in lab
- great potential for developing future therapies to cure diseases
Disadvantages of embryonic stem cells for scientists
Potentially ethically problematic as blostocyst must be destroyed when cells are removed
egg donation is also an issue
