20.2 Stem cells and totipotency Flashcards
How do cells of a multicellular organism differ from single celled organisms
- In single celled, they perform all life functions in a single cell but can’t be very efficient as each function requires different enzymes etc
- Multicellular organisms have cells each adapted to perform a particular role
How are all cells in humans similar
They all contain the same genes as they are derived from mitotic divisions of the fertilised egg (zygote).
So eg a cell in lining of small intestine has a gene coding for insulin just how a beta cell in pancreas has the gene coding for maltase.
However, although all cells contain the same genes, only certain genes are expressed.
What genes are permanently switched on in all cells
What ones are switched off
Genes that code for essential chemicals eg enzymes for respiration, or enzymes for transcription, translation etc.
In cells lining the small intestine, the insulin gene is switched off.
What are totipotent cells
Organisms develop from a single fertilised egg, which has ability to give rise to all types of cell.
So cells such as these can mature into any type of body cells so are totipotent cells.
These later differentiate to become specialised to perform a specific function. Mesophyll cells for photosynthesis, or muscle cells for contraction.
How do cells become specialised
- Only some genes are expressed during specialisation so only part of the DNA of a cell is translated into proteins.
Cell only makes proteins it requires to carry out its specialised function.
So although the cell is capable of making other proteins, they are not needed so cell won’t waste energy and resources making them.
How are genes prevented from being expressed
- Prevent transcription so prevent production of mRNA
- Prevent translation
If specialised cells still contain all the genes of the organism, can they still develop into any cell?
Depends
Xylem vessels lose their nuclei so they can transport the maximum amount of water and so do red blood cells. As nucleus contains all the genes, these obviously can’t develop into other cells.
What are stem cells
These are cells that retain the ability to differentiate into other cells
So undifferentiated dividing cells in adult tissues and need to be constantly replaced. They can divide to form an identical copy of themselves in process called self renewal.
What 4 places do stem cells come from in mammals
- Embryonic ones come from embryos as they’re developing. They can divide into any cell at this stage.
- Umbilical cord ones come from umbilical cord, and are similar to adult stem cells
- Placental ones are found in placenta and can develop into specific types of cells
- Adult stem cells are found in body tissue of fetus through to the adult. Specific to a particular organ or tissue where they produce cells to maintain and repair tissues .
What are totipotent stem cells
Found in early embryo
They can differentiate into any type of cell. Since all body cells are formed from a zygote, the zygote is totipotent.
As the zygote matures, the cells develop into slightly more specialised cells called pluripotent stem cells
What are pluripotent stem cells
Found in embryos and can differentiate into almost any cell
What are multipotent stem cells
Found in adults and can differentiate into a limited number of specialised cells
Eg stem cells in bone marrow can produce any type of blood cell
Eg umbilical cord and adult stem cells
What are unipotent stem cells
Can only differentiate into a single type of cell. Derived from multipotent stem cells and are made in adult tissue.
Eg cardiomyocytes are heart muscle cells that can divide to produce new heart tissue to repair damaged muscle
What are induced pluripotent stem cells
Type of pluripotent cell that is produced from unipotent stem cell
Genetically alter body cell in lab to acquire characteristics of an embryonic stem cell. Induce genes and use transcriptional factors to do this.
So turns on genes that are otherwise turned off
IPS cells are similar to embryonic stem cells but there are differences:
Although they express some of the same genes that are usually expressed in embryonic stem cell, they aren’t exact duplicates of them.
They are capable of self renewal so can potentially divide to provide a limitless supply.
This means they can replace embryonic stem cells in research so overcome ethical issues of using embryos
How are pluripotent cells used to treat human disorders
- Regrow tissues that have been damaged in some way eg from an accident, or a disease
B cells of pancreas for type 1 diabetes
Skin cells for burns and wounds
Heart muscle cells for heart damage
