Module 8 - Gene expression is controlled by a number of features

Question 1

Define stem cells

Answer 1

Will keep dividing, undifferentiated

Question 2

Define totipotent cells

Answer 2

Can become any type of cell (only very early embryonic stem cells)

Question 3

Define pluripotent cells

Answer 3

Can become many types of cells- found in embryos- can divide in unlimited numbers- used to treat diseases

Question 4

Define multipotent cells

Answer 4

Found in adult- limited

Question 5

Define unipotent cells

Answer 5

Only can differentiate into cardiomyocytes

Question 6

Define induced pluripotent stem cells (iPS cells)

Answer 6

Can now be made from adult body cells (somatic)- genes ‘turned on and off’

Question 7

2 marks

Oestrogen is a hormone that affects transcription. It forms a complex with a receptor in the cytoplasm of target cells. Explain how an activated oestrogen receptor affects the target cell.

Answer 7

1. Receptor / transcription factor binds to promoter which stimulates RNA polymerase
2. Increase transcription

Question 8

1 marks

Oestrogen only affects target cells. Explain why oestrogen does not affect other cells in the body

Answer 8

Other cells do not have the oestrogen receptors

Question 9

2 marks

Steroid hormones are hydrophobic.
Explain why steroid hormones can rapidly enter a cell by passing through its cell-surface membrane.

Answer 9

1. Lipid soluble
2. Diffuse through phospholipid bilayer

Question 10

3 marks

The binding of testosterone to an AR changes the shape of the AR. This AR molecule now enters the nucleus and stimulates gene expression.
Suggest how the AR could stimulate gene expression.

Answer 10

1. AR is a transcription factor
2. Binds to DNA
3. Stimulates RNA polymerase

Question 11

2 marks

Define what is meant by epigenetics.

Answer 11

1. Heritable changes in gene function
2. Without changes to the base sequence of DNA

Question 12

3 marks

Explain how increased methylation could lead to cancer.

Answer 12

1. Methyl groups could be added to both copies of a tumour suppressor gene
2. The transcription of tumour suppressor genes is inhibited
3. Leading to uncontrolled cell division

Question 13

Tumour suppressor gene

Answer 13

These genes produce proteins to slow down cell division and to cause cell death if DNA copying errors are detected

Question 14

3 marks

MDS can develop from epigenetic changes to tumour suppressor genes. In some patients, the drug AZA has reduced the effects of MDS. AZA is an inhibitor of DNA methyltransferases. These enzymes add methyl groups to cytosine bases. Suggest and explain how AZA can reduce the effects of MDS in some patients.

Answer 14

1. AZA reduces methylation of DNA
2. Tumour suppressor gene is transcribed/expressed
3. Prevents uncontrollable cell division

Question 15

Regulation of transcription- transcription factors

Answer 15

1. Oestrogen steroid hormone- diffuses across phospholipid bilayer (lipid soluble)
2. Binds to a transcription factor
3. Transcription factor changes tertiary structure to make it more complementary to promotor region of DNA
4. Transcription factor binds to promoter
5. Stimulates RNA polymerase to bind
6. Increased transcription of a gene (e.g. oncogene)
7. Cancer medicine could block the binding of oestrogen due to similar structure.

Question 16

Regulation of transcription- Epigenetics

Answer 16

1. A heritable change in the gene function without a change to the base sequence of DNA
2. Methyl groups bind to cytosine, Acetyl groups bind to histone proteins
3. Increased methylation/ decreased acetylation= histone proteins come closer
4. Transcription factors and RNA polymerase cannot bind to promoter region of gene (e.g. tumour suppressor gene or oncogene)
5. Cancer drugs could ‘turn on’ tumour suppressor genes and ‘turn off’ oncogenes

Question 17

Regulation of translation- RNA interference

Answer 17

1. Single strand of RNA (small interfering RNA- siRNA) binds to mRNA
2. Translation is prevented- anticodon blocked from reaching codon
3. Somtimes the mRNA is destroyed by the siRNA if enzyme attached too
4. Cancer drugs could prevent translation of an oncogene

Question 18

Define malignant tumour

Answer 18

Uncontrolled mitosis, unspecialised cells, metastasise

Question 19

Define oncogene

Answer 19

Could cause expression of excessive growth factor protein or distortion of receptor protein= uncontrolled mitosis

Question 20

Define tumour suppressor gene

Answer 20

Could cause expression of proteins that cause apoptosis= death of tumour cells

Question 21

2 marks

Not all mutations result in a change to the amino acid sequence of the encoded polypeptide. Explain why.

Answer 21

1. Genetic code degenerate
2. Mutation in intron