Topic 8—A: Mutations and gene expression- 5. Stem cells

Question 1

What are multicellular organisms made up from?

Answer 1

• many different cell types that are specialised for their function e..g liver cells, muscle cells, white blood cells

Question 2

Where did these specialised cell types originally come from?

Answer 2

• stem cells

Question 3

What are stem cells?

Answer 3

• they are unspecialised cells that can develop into other types of cell
• stem cells divide to become new cells, which then become specialised

Question 4

Where are stem cells found?

Answer 4

• 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)

Question 5

Totipotent cells

Answer 5

• 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)

Question 6

Where are totipotent stem cells only present?

Answer 6

• they are only present in mammals in the first few cell divisions of an embryo
• after this point the embryonic stem cells become pluripotent

Question 7

Pluripotent cells

Answer 7

• stem cells that can still specialise into any type of cell in the body, but lose the ability to become the cells that make up the placenta

Question 8

What are the stem cells present in adult mammals either?

Answer 8

• multipotent
• unipotent

Question 9

Multipotent

Answer 9

• stem cells are able to differentiate into a few different types of cell
  E.g. both red and white blood cells can be formed from multipotent stem cells found in bone marrow

Question 10

Unipotent

Answer 10

• stem cells can only differentiate into one type of cell
  E.g. 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

Question 11

Why do stem cells become specialised?

Answer 11

• Brcause 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 transited (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

Question 12

What happens to genes that are expressed?

Answer 12

• they 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 become specialised it stays specialised

Question 13

What are cardiomyocytes?

Answer 13

• they 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 means 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 become worn out though age
• recent research however, has suggested that our earths do have some regenerative capability
• some scientists now think that old or damaged cardiomyocytes can be replaced by new cardiomyocystes derives from a small sample 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 its a really slow process and that it’s possible that some cardiomyocytes are never replaced throughout a persons entire lifetime
• others think that it’s occurring more quickly, so that every cardiomyocyte in the heart is replaced several times in a lifetime