5. Stem Cells

Question 1

Stem cells

Answer 1

All multicellular organisms are made up from many different cell types that are specialised for their function eg liver cells.

All these specialised cells originally came from stem cells.

Stem cells are unspecialised they develop into other types of cells. They divide when they become specialised

Question 2

Where are stem cells found ?

Answer 2

Embryos ( where they become all the specialised cells needed to form fetus)

Adult tissues ( where they become specialised cells that need to be replaced)

Question 3

Name a cell which constantly needs replacing ?

Answer 3

Stem cells in intestines in intestinal epithelial cells

Question 4

Totipotent cells

Answer 4

Can mature into any type of body cell in an organism ( including placenta)

They’re only present in mammals in first few cell divisions of embryo.
After this pony they become pluripotent.

Question 5

Pluripotent

Answer 5

They still specialise into any cell in body but lose ability to become the cells that make up placenta

Question 6

What are the stem cells present in adult mammals ?

Answer 6

Multipotent - differentiate into few different types of cells

Unipotent - differentiate into okay type of cell

Question 7

Example of multipotent

Answer 7

Both red blood and white blood cells formed form multipotent stem cells found in bone marrow.

Question 8

Example unipotent

Answer 8

Divide to produce epidermal skin cells , make up outer layer of skin

Question 9

How do stem cells become specialised ?

Answer 9

During their development they only transcribe and translate part of their DNA.

They contain same genes but not all of them are transcribed and translated.

Under1 set of conditions certain genes are expressed and others switched off.

Under2 set of conditions different genes are expressed and others switched off.

Question 10

What is the process of cells becoming specialised known as ?

Answer 10

Differentiation

Question 11

So what do the genes that get expressed do ?

Answer 11

Get transcribed into mRNA, which is then translated into proteins.

These proteins modify cell - structure / control cell processes

Changes to the cell produced by these proteins causes cell to become specialised. (Difficult to reverse so once a cell has specialised it stays that way)

Question 12

So what happens if genes are switched off ?

Answer 12

The mRNA is not transcribed or translated and no proteins are produced to modify the cell.

So cell doesn’t become specialised.

Question 13

Example

Red blood cells

Answer 13

Produced by stem cell in bone marrow.

Contain lots of haemoglobin that have no nucleus (make room for more haemoglobin)

Stem cell produces new cell in which genes for haemoglobin production are expressed

Other genes ie ones that remove nucleus are expressed too.

Many other genes not expressed so switched off resulting in specialised red blood cells

Question 14

Example

Nerve cells

Answer 14

They have long axons and dendrites which Connect them to other nerve cells.

Produced from stem cells in neural tube.

Stem cells produce new cells in which genes that direct axon to extend outwards are expressed.

Genes that direct the dendrites are also expressed.

Many other genes switched off.

Question 15

Cardiomyocytes

Answer 15

Heart muscle cells that make up lots of tissue in our hearts.

Question 16

What was initially thought about cardiomyocytes in mature mammals ?

Answer 16

They couldn’t divide to replicate themselves.

Meaning we weren’t able to regenerate own heart cells.

Major problem if heart becomes too damaged by heart attack / age

Question 17

However what has recent research suggested about our heart ?

Answer 17

We have some regenerative capability

Old / damaged cardiomyocytes replaced by new cardiomyocytes derived from small supply of unipotent stem cells in heart .

Some Scientists think this process is slow and some heart cells can’t replace themselves through persons life.
Others think it’s occurring quickly so every heart cell is replaced several times in life.