Gene Expression And Cancer Flashcards
What’s the difference between benign tumours and malignant rumours
Non cancerous are called benign and cancerous are called malignant
Compare the characteristics of benign and malignant tumours
B- can grow to a large size
M- can also grow to a large size
B- grow very slowly
M- grow rapidly
B- cells are often specialised
M- cells become unspecialised
B- cells produce adhesion molecule that make them stick together and so they remain within the tissue from which they arise=primary tumours
M- cells do not produce adhesion molecule and so tend to spread to other regions of the body, a process called metastasis, forming secondary tumours
B- tumours surrounded by a capsule of dense tissue (compact structure )
M- tumours not surrounded by a capsule and so can grow finger like projections into the surrounding tissue
B- much less likely to be life threatening but can disrupt functioning of a vital organ
M- more likely to be life threatening, as abnormal tumour tissue replaces normal tissue
B- tend to have localised effects on the body
M- often have whole body effects such as Weight loss or disease
B- can usually be removed by surgery alone
M- removal usually involves radiotherapy or chemotherapy as well as surgery
B- rarely reoccur after treatment
M- more frequently reoccur after treatment
What do proto-oncogenes do
Stimulate a cell to divide when growth factors attach to a protein receptor on its cell surface membrane
This then activated genes that fuse DNA to replicate and the cell to divide
What are the two reasons why if a proto-oncogene mutates into an oncogene it can become permanently activated
The receptor protein on a cell surface membrane can be permanently activated, so that cell division is switched on even in the absence of growth factors
The oncogene May code for a growth factor that is then produced in excessive amounts, again stimulating excessive cell division
What do tumour suppressor genes do
Slow down cell division
, repair mistakes in DNA and tell when to die (apoptosis)
What does a normal tumour suppressor gene do
It maintains normal rates of cell division and so prevents the formation of tumours
What happens if a tumour suppressor gene becomes mutated
It is in activated. As a result it stops inhibiting cell division and cells can grow out of control
The mutated cells that are formed are usually structurally and functionally different from normal cells. While most of these die, those that survive can make clones of themselves and form tumours
How are some cancers developed by oncogenes and tumour suppressor genes
Can be caused by mutations of proto-oncogenes that cause the oncogene to be activated
Can be caused by inherited mutations of tumour suppressor genes but most are required not inherited
What is an important difference between oncogenes and tumour suppressor genes
Is that while oncogenes cause cancer as a result of activation of proto-oncogenes, tumour suppressor genes cause cancer when they are inactivated
How may hypermethylation ( increase methylation) lead to cancer
- hypermethylation occurs in a specific region( promoter region) of tumour suppressor genes
- This leads to the tumour suppressor gene being inactivated
- As a result, transcription of the protester regions of tumour suppressor genes is inhibited
- The tumour suppressor gene is therefore silenced
- As the tumour suppressor gene normally slows the rate of cell division, it’s inactivation leads to increased cell division and the formation of a tumour
What is hypomethylation
Found to occur in oncogenes where it leads to their activation and hence the formation of tumours
Why is there a greater risk of breast cancer after the menopause
Due to increased oestrogen concentrations
How might oestrogen cause breast cancer in post menopausal women
Fat cells of the breast tend to produce more oestrogen after the menopause. These locally produced oestrogens release an inhibitor molecule that prevents transcription causing proto-oncogenes of breast tissue to develop into oncogenes. These oncogenes increase the rate of cell division leading to the development of a tumour (Breast cancer )
Explain why the activation of proto-oncogenes can cause the development of a tumour while it requires deactivation of a tumour suppressor gene to do so
Proto-oncogenes increase the rate of cell division and so their activation produces a mass of cells (tumour) but tumour suppressor genes decrease the rate of cell Division and so their deactivation produces a tumour
Suggest why surgical removal of a malignant tumour requires follow up treatments such as chemotherapy and radiotherapy
Cells of a benign tumour produce adhesion molecules that make them stick together and are surrounded by a capsule of dense tissue. The tumour therefore remains as a compact structure and so surgical removal is likely to remove all tumour cells
