The Control of Gene Expression: Gene Expression is Controlled by a Number of Features - Most of a Cell's DNA is Not Translated

Question 1

What are stem cells?

Answer 1

• Undifferentiated cells that can divide indefinitely and turn into other specific cell types

Question 2

What are the different types of stem cells?

Answer 2

• Totipotent cells
• Pluripotent cells
• Multipotent cells
• Unipotent cells

Question 3

Totipotent cells

Answer 3

• Stem cells that can mature into any type of body cell (including cells that form placenta in mammals)
• Present in mammals in first few cell divisions of an embryo

Question 4

Pluripotent cells

Answer 4

• Stem cells that can differentiate into any type of body cell, except cells that form placenta
• After first few cell divisions of embryo, totipotent cells become pluripotent

Question 5

Multipotent cells

Answer 5

• Stem cells that can differentiate into a few cell types

- Found in mature mammals

Question 6

Unipotent cells

Answer 6

• Stem cells that can differentiate into one type of cell

- Found in mature mammals

Question 7

Give an example of the use of unipotent cells

Answer 7

• Unipotent cells form cardiomyocytes (heart muscle cells)

- Cardiomyocytes can regenerate

Question 8

Do stem cells contain different genes to other cells?

Answer 8

• No

- Stem cells all contain the same genes but not all are expressed

Question 9

How do stem cells differentiate into specialised cells?

Answer 9

• Stem cells only transcribe and translate part of their DNA
• Certain genes are expressed and other switched off
• Expressed genes are transcribed into mRNA
• mRNA translated into proteins
• These proteins modify the cell, determining cell structure and control cell processes including the expression of more genes
• Changes to the cell caused by these proteins cause the cell to be specialised

Question 10

Can cell specialisation be reversed?

Answer 10

• Changes are difficult to reverse so specialised cells tend to stay specialised

Question 11

Induced pluripotent stem cells (iPS cells)

Answer 11

• Created in a lab
• Involves ‘reprogramming’ specialised adult body cells so they become pluripotent
• Specialised adult cells made to express various transcription factors
• Transcription factors cause adult cells to express genes associated with pluripotency

Question 12

What are transcription factors?

Answer 12

• Proteins that control whether or not genes are transcribed

Question 13

How can transcription factors be introduced to adult cells to create iPS cells?

Answer 13

• By infecting adult cells with a specially-modified virus
• Virus has genes coding for transcription factors within its DNA
• When virus infects cell, these genes are passed into adult cell’s DNA so cell can produces the transcription factors

Question 14

What are the potential benefits of iPS cells?

Answer 14

• Potentially can differentiate into any cell (except placenta cells); more flexible than multipotent and unipotent cells
• Doesn’t require destruction of embryo cells
• Stem cells can be obtained with consent
• Could be made from patient’s own cells, reducing chance of rejection

Question 15

What are the ethical debates surrounding the use of stem cells from embryos created by IVF?

Answer 15

• Artificially activated eggs

• Some people have fewer objections to stem cells obtained from egg cells that haven’t been fertilised by sperm, but have been artificially activated to start dividing
• Cells wouldn’t survive past few days and wouldn’t produce foetus if placed in womb

• Right to life
- Some believe that from fertilisation the individual has a right to life

• Destruction of embryo

• Stem cells from embryos made via IVF results in the destruction of an embryo that could form a foetus
• Some think only adult stem cells should be used as doesn’t destroy embryos

Question 16

What are the benefits of stem cell therapy?

Answer 16

• Could save many lives
- Stem cells could grow organs so less people die waiting for a donor organ

• Lower chance of rejection
- May be possible to make stem cells genetically identical to a patient’s own cells

• Could improve quality of life