A5. Stem Cells Flashcards
What are stem cells? (3 points)
- Multicellular organisms are made up from many different cell types that are specialised for their function, e.g. liver cells, muscle cells, white blood cells. All these specialised cell types originally came from stem cells.
- Stem cells are unspecialised cells that can develop into other types of cell.
- Stem cells divide to become new cells, which then become specialised.
Where are stem cells found?
All multicellular organisms have some form of stem cell. Stem cells are found in the _______(where they become all the specialised cells needed to form a fetus) and in _____ _____ _______(where they become specialised cells that need to be replaced, e.g. stem cells in the intestines constantly replace intestinal epithelial cells).
What are totipotent cells and where are they found?
When do pluripotent cells form and what can they do/not do?
Where are multipotent and unipotent cells found?
What can multipotent cells do and an example?
What can unipotent cells do and an example?
All multicellular organisms have some form of stem cell. Stem cells are found in the embryo (where they become all the specialised cells needed to form a fetus) and in some adult tissues (where they become specialised cells that need to be replaced, e.g. stem cells in the intestines constantly replace intestinal epithelial cells).
Stem cells that can mature (develop) into any type of body cell in an organism, (including the cells that make up the placenta in mammals) are called totipotent cells. Totipotent stem cells are only present in mammals in the first few cell divisions of an embryo.After this point the embryonic stem cells become pluripotent. They can still specialise into any cell in the body, but lose the ability to become the cells that make up the placenta.
The stem cells present in adult mammals are either multipotent or unipotent.
Multipotent stem cells are able to differentiate into a few different types of cell.
Example
Both red and white blood cells can be formed from multipotent stem cells found in bone marrow.
Unipotent stem cells can only differentiate into one type of cell.
Example
There’s a type of unipotent stem cell that can only divide to produce epidermal skin cells, which make up the outer layer of your skin.
Becoming specialised
Stem cells become specialised because during their development they only ___________ and _________ part of their ____. Stem cells all contain the same _____- but during development not all of them are ______________ and _____________(_____________). Under one set of conditions, certain genes are __________and others are ___________ ____. Under different conditions, different genes are expressed and others are switched off.
Genes that are expressed get ____________into _____, which is then ____________into __________. These _______ modify the cell-they determine the cell structure and control cell processes (including the expression of more genes, which produces more proteins).
Changes to the cell produced by these proteins cause the cell to become specialised. These changes are difficult to reverse, so once a cell has specialised it stays specialised.
Becoming specialised
Stem cells become specialised because during their development they only transcribe and translate part of their DNA. Stem cells all contain the same genes- but during development not all of them are transcribed and translated (expressed). Under one set of conditions, certain genes are expressed and others are switched off. Under different conditions, different genes are expressed and others are switched off.
Genes that are expressed get transcribed into mRNA, which is then translated into proteins. These proteins modify the cell-they determine the cell structure and control cell processes (including the expression of more genes, which produces more proteins).
Changes to the cell produced by these proteins cause the cell to become specialised. These changes are difficult to reverse, so once a cell has specialised it stays specialised.
Figure 3: Summary of how cells become specialised through gene expression.
Example 1 - red blood cells
Red blood cells are produced from a type of stem cell in the ____ __________. They contain lots of _______________and have no ________(to make room for more haemoglobin). The stem cell produces a new cell in which the ______for haemoglobin production are ____________. Other genes, such as those involved in removing the nucleus, are ____________too. Many other genes are not expressed (_________ ___), resulting in a specialised red blood cell.
Red blood cells are produced from a type of stem cell in the bone marrow. They contain lots of haemoglobin and have no nucleus (to make room for more haemoglobin). The stem cell produces a new cell in which the genes for haemoglobin production are expressed. Other genes, such as those involved in removing the nucleus, are expressed too. Many other genes are not expressed (switched off), resulting in a specialised red blood cell.
Example 2 - nerve cells
Nerve cells have long axons and dendrites (branches), which connect them to other nerve cells. They’re produced from stem cells in the ________ ____. The stem cells produce new cells in which the genes that direct the axon to extend outwards are expressed. Genes that direct the dendrites to form are also _____________. Many other genes are switched off.
Nerve cells have long axons and dendrites (branches), which connect them to other nerve cells. They’re produced from stem cells in the neural tube. The stem cells produce new cells in which the genes that direct the axon to extend outwards are expressed. Genes that direct the dendrites to form are also expressed. Many other genes are switched off.
Cardiomyocytes
Cardiomyocytes are heart muscle cells that make up a lot of the tissue in our hearts. In mature mammals, it’s thought that they can’t divide to ___________themselves. This meant that for ages, everyone thought that we weren’t able to ____________ our own heart cells at all. This is a major problem if the heart becomes damaged, e.g. by a heart attack, or the cells became worn out through age.
Recent research however, has suggested that our hearts do have some ________________ capability. Some scientists now think that old or damaged cardiomyocytes can be replaced by new cardiomyocytes derived from a small supply of unipotent stem cells in the heart.
Some researchers think that this process could be constantly occurring, but haven’t yet agreed on ___ ________ __ __________. Some believe that it’s a really ____process and that it’s possible that some cardiomyocytes are never replaced throughout a person’s entire lifetime. Others think that it’s occurring more _______, so that every cardiomyocyte in the heart is replaced several times in a lifetime.
Cardiomyocytes
Cardiomyocytes are heart muscle cells that make up a lot of the tissue in our hearts. In mature mammals, it’s thought that they can’t divide to replicate themselves. This meant that for ages, everyone thought that we weren’t able to regenerate our own heart cells at all. This is a major problem if the heart becomes damaged, e.g. by a heart attack, or the cells became worn out through age.
Recent research however, has suggested that our hearts do have some regenrative capability. Some scientists now think that old or damaged cardiomyocytes can be replaced by new cardiomyocytes derived from a small supply of unipotent stem cells in the heart.
Some researchers think that this process could be constantly occurring, but haven’t yet agreed on how quickly it happens. Some believe that it’s a really slow process and that it’s possible that some cardiomyocytes are never replaced throughout a person’s entire lifetime. Others think that it’s occurring more quickly, so that every cardiomyocyte in the heart is replaced several times in a lifetime.
