Cancer Genetics

Question 1

Describe Benign Tumours

Answer 1

• slow growth
• expands in the same tissue
• doesn’t spread
• nearly normal cell differentiation

Question 2

Describe malignant tumours

Answer 2

• rapid growth
• invades surrounding tissues
• metastasises via the blood stream & lymphatic system
• poor cell differentiation

Question 3

What are some of the general cancer phenotypes ?

Answer 3

• loss of cell death
• loss of gap junctions
• loss of contact inhibition
• autocrine stimulation

Question 4

Describe what happens as a result of autocrine stimulation in cancer cells ?

Answer 4

• tumour cells make their own signals to divide

Question 5

Describe what happens as a result of loss of contact inhibition in cancer cells ?

Answer 5

• unable to stop dividing when contacted by another cell

Question 6

Describe what happens as a result of loss of cell death in cancer cells ?

Answer 6

• resistance to programmed cell death

Question 7

Describe what happens as a result of loss of gap junctions in cancer cells ?

Answer 7

no channels for connecting to neighbour cell

Question 8

Define Angiogenesis

Answer 8

• secretion of substances that cause blood vessel to grow towards tumour

Question 9

What are some examples of tumour viruses ?

Answer 9

• Cervical cancer - HPV
• Burkitt’s Lymphoma - EBV
• Hepatocellular carcinoma - hepatitis viruses

Question 10

How does cancer arise ?

Answer 10

• successive mutations in a clone of proliferating cells

Question 11

Loss of normal control arise from mutations in what 3 genes ?

Answer 11

• proto-oncogenes
• tumour suppressor genes
• DNA repair enzymes

Question 12

How do proton-oncogenes transform into dominant oncogenes

Answer 12

• point mutations
• partial deletion mutations
• gene amplification resulting in over expression

Question 13

Describe the TP53 gene and what it encodes for

Answer 13

• TP53 encodes for the p53 protein, which acts as a tumour suppressor
• p53 monitors the cell cycle, triggers cell cycle arrest, apoptosis or DNA repair

Question 14

Describe the Retinoblastoma

Answer 14

• retinoblastoma protein - Rb
• involved in cell cycle regulation
• controls G1 to S transition

Question 15

What occurs when there’s a mutation in the Rb protein

Answer 15

• the mutation leads to the loss of the inhibitory effect of Rb and allows uncontrolled cell division

Question 16

What are key attributes of tumour suppressor genes ?

Answer 16

1. familial cancer syndromes
2. inactivation in common human cancers (loss of heterozygosity)
3. recessive at a cellular level
4. two-hit hypothesis

Question 17

Describe loss of heterozygosity

Answer 17

• 2 copies of each gene
• 1 is lost or inactivated
• only 1 remains so its no longer heterozygous
• 1 copy of a defective gene is the same as no gene

Question 18

Describe the two-hit hypothesis in regards to cancer

Answer 18

• at least 2 mutations are required for cancer
• a single mutation means there is potential for cancer formation

Question 19

Describe how cell cycle checkpoints work

Answer 19

• DNA damage signals cell cycle checkpoints
• if damage is too great to fix by repair a signal is sent for the cell to undergo apoptosis