Module 8 - Gene expression is controlled by a number of features Flashcards
Define stem cells
Will keep dividing, undifferentiated
Define totipotent cells
Can become any type of cell (only very early embryonic stem cells)
Define pluripotent cells
Can become many types of cells- found in embryos- can divide in unlimited numbers- used to treat diseases
Define multipotent cells
Found in adult- limited
Define unipotent cells
Only can differentiate into cardiomyocytes
Define induced pluripotent stem cells (iPS cells)
Can now be made from adult body cells (somatic)- genes ‘turned on and off’
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.
- Receptor / transcription factor binds to promoter which stimulates RNA polymerase
- Increase transcription
1 marks
Oestrogen only affects target cells. Explain why oestrogen does not affect other cells in the body
Other cells do not have the oestrogen receptors
2 marks
Steroid hormones are hydrophobic.
Explain why steroid hormones can rapidly enter a cell by passing through its cell-surface membrane.
- Lipid soluble
- Diffuse through phospholipid bilayer
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.
- AR is a transcription factor
- Binds to DNA
- Stimulates RNA polymerase
2 marks
Define what is meant by epigenetics.
- Heritable changes in gene function
- Without changes to the base sequence of DNA
3 marks
Explain how increased methylation could lead to cancer.
- Methyl groups could be added to both copies of a tumour suppressor gene
- The transcription of tumour suppressor genes is inhibited
- Leading to uncontrolled cell division
Tumour suppressor gene
These genes produce proteins to slow down cell division and to cause cell death if DNA copying errors are detected
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.
- AZA reduces methylation of DNA
- Tumour suppressor gene is transcribed/expressed
- Prevents uncontrollable cell division
Regulation of transcription- transcription factors
- Oestrogen steroid hormone- diffuses across phospholipid bilayer (lipid soluble)
- Binds to a transcription factor
- Transcription factor changes tertiary structure to make it more complementary to promotor region of DNA
- Transcription factor binds to promoter
- Stimulates RNA polymerase to bind
- Increased transcription of a gene (e.g. oncogene)
- Cancer medicine could block the binding of oestrogen due to similar structure.
Regulation of transcription- Epigenetics
- A heritable change in the gene function without a change to the base sequence of DNA
- Methyl groups bind to cytosine, Acetyl groups bind to histone proteins
- Increased methylation/ decreased acetylation= histone proteins come closer
- Transcription factors and RNA polymerase cannot bind to promoter region of gene (e.g. tumour suppressor gene or oncogene)
- Cancer drugs could ‘turn on’ tumour suppressor genes and ‘turn off’ oncogenes
Regulation of translation- RNA interference
- Single strand of RNA (small interfering RNA- siRNA) binds to mRNA
- Translation is prevented- anticodon blocked from reaching codon
- Somtimes the mRNA is destroyed by the siRNA if enzyme attached too
- Cancer drugs could prevent translation of an oncogene
Define malignant tumour
Uncontrolled mitosis, unspecialised cells, metastasise
Define oncogene
Could cause expression of excessive growth factor protein or distortion of receptor protein= uncontrolled mitosis
Define tumour suppressor gene
Could cause expression of proteins that cause apoptosis= death of tumour cells
