20.5 Gene expression and cancer

Question 1

What are the two types of tumour

Answer 1

1. Benign - being (its chill)

2. Malignant - Malicious (its not chill)

Question 2

Properties of benign tumours

Answer 2

• Grow to a large size
• Grow slowly
• Cell nucleus looks normal
• Well differentiated cells
• Produce adhesion molecules that make them stick together
• Tumours are surrounded by a capsule of dense tissue and so remain as a compact structure
• Much less likely to be lethal
• Tend to have localised effects
• Can be removed by surgery alone
• Rarely occur after treatment

Question 3

Properties of malignant tumours

Answer 3

• Grow to a large size as well
• Grow rapidly
• Cell nucleus is darker due to to an abundancce of DNA
• Cells are un-differentiated
• Cells do not produce adhesion molecules so spread to other parts of the body, forming secondary tumours in a process called metastasis
• Tumours are not surrounded by a capsule so therefore grow fingerlike projections that grow into other tissues
• More likely to be lethal
• Have whole body effects like weight loss and fatigue
• Removal involves radiotherapy and surgery
• More frequently reoccur after treatment

Question 4

What are oncogenes

Answer 4

Mutations of proto-oncogenes.

Question 5

What do proto-oncogenes do

Answer 5

Stimulate a cell to divide when growth factors attach to a protein receptor on its cell membrane. This then activates genes that cause DNA to replicate and the cell to divide.

Question 6

What happens when a proto-oncogene becomes mutated

Answer 6

It becomes permanently switched on

Question 7

What are the two reasons for permanent oncogene activation

Answer 7

1. The receptor protein on the cell membrane can be permanently activated, so cell division is switched on even in the absence of growth factors
2. The oncogene may code for a growth factor that is produced excessively, again stimulating excessive cell division

Question 8

What are tumour suppressor genes

Answer 8

Genes that slow down cell divison, repair mistakes and carry out apoptosis. They have the opposite role to proto-oncogenes.

Question 9

How can hypermethylation lead to cancer

Answer 9

1. Hypermethylation occurs in a specific region (promoter region) of tumour suppressor genes
2. This leads to the tumour suppressor gene being inactivated
3. As a result, transcription of the promoter regions of tumour suppressor genes is inhibited
4. The tumour suppressor gene is therefore silenced
5. As the tumour suppressor gene normally slows the rate of cell division, its inactivation leads to increased cell division and the formation of a tumour

Question 10

Why does a womans risk of developing breast cancer increases following menopause

Answer 10

The fat cells of the breasts tend to produce more oestrogens after menopause. This leads to breast cancer

Once a tumour develops, it further increases oestrogen concentration which therefore leads to increased tumour development.