Gene expression and cancer

Question 1

What are the types of tumour?

Answer 1

• malignant tumours
• benign tumours

Question 2

What are the features of benign tumours?

Answer 2

• grow slowly
• nucleus has a relatively normal appearance
• often well - differentiated
• produce adhesions that mean they stick together and they remain in tissue
• surrounded by a capsule of deep tissue so remains compact
• localised effect

Question 3

What are the features of malignant tumours?

Answer 3

• grow rapidly
• nucleus is larger and appears darker due to the abundance of DNA
• de - differentiated
  -does not produce adhesions so they tend to spread around the body (metastatis)
• not surounded by a tissue, grow projections
• systematic effect

Question 4

What are the genes that play a role in cancer?

Answer 4

• tumour supressor genes
• oncogenes

Question 5

What are oncogenes?

Answer 5

• most oncogenes are mutations of proto - oncogenes
• proto - oncogenes stimulate a cell to divide when growth factors attach to a protein receptor on its cell surface membrane
• This activates genes and causes cells to divide
• if a proto - oncogene mutates into an oncogene:
• the receptor protein on the cell surface membrane can be permenantly activated, so cell division continues even in the absence of growth factors
• the oncogene may code for a growth factor in excessive amounts, stimulating cell division

Question 6

What are tumour - suppressor genes?

Answer 6

• tumour supressor genes slow down cell division and repair mistakes in DNA and cause apoptosis
• they also maintain normal rates of cell division and prevent the formation of tumours
• if a tumour supressor gene is turned off, it stops inhibiting cell division and cells can grow out of control

Question 7

What is the abnormal methylation of tumour supressor genes?

Answer 7

• hypermethylation can lead to cancer
• this occurs in the promoter reigons of the tumour supressor gene
• This leads to a tumour supressor gene being inactivated. As a result transcription is prevented and the gene is silenced
• Therefore, tumour formation is not prevented

Question 8

What occurs when oncogenes are hypomethylated?

Answer 8

• This is reduced methylation
• this leads to their activation and the formation of tumours

Question 9

What is the role of oestrogen and breast cancer?

Answer 9

• oestrogen increases after menopause
• oestrogen can activate a gene by binding to a gene which promotes transcription
• if the gene controls cell division and growth, it will be activated and lead to continued division which can produce a tumour
• Additionally, once a tumour is formed, it further increases oestrogen concentations which leads to the further development of the tumour as WBC are also drawn to the tumours