Cancer Genetics Flashcards
Describe Benign Tumours
- slow growth
- expands in the same tissue
- doesn’t spread
- nearly normal cell differentiation
Describe malignant tumours
- rapid growth
- invades surrounding tissues
- metastasises via the blood stream & lymphatic system
- poor cell differentiation
What are some of the general cancer phenotypes ?
- loss of cell death
- loss of gap junctions
- loss of contact inhibition
- autocrine stimulation
Describe what happens as a result of autocrine stimulation in cancer cells ?
- tumour cells make their own signals to divide
Describe what happens as a result of loss of contact inhibition in cancer cells ?
- unable to stop dividing when contacted by another cell
Describe what happens as a result of loss of cell death in cancer cells ?
- resistance to programmed cell death
Describe what happens as a result of loss of gap junctions in cancer cells ?
no channels for connecting to neighbour cell
Define Angiogenesis
- secretion of substances that cause blood vessel to grow towards tumour
What are some examples of tumour viruses ?
- Cervical cancer - HPV
- Burkitt’s Lymphoma - EBV
- Hepatocellular carcinoma - hepatitis viruses
How does cancer arise ?
- successive mutations in a clone of proliferating cells
Loss of normal control arise from mutations in what 3 genes ?
- proto-oncogenes
- tumour suppressor genes
- DNA repair enzymes
How do proton-oncogenes transform into dominant oncogenes
- point mutations
- partial deletion mutations
- gene amplification resulting in over expression
Describe the TP53 gene and what it encodes for
- 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
Describe the Retinoblastoma
- retinoblastoma protein - Rb
- involved in cell cycle regulation
- controls G1 to S transition
What occurs when there’s a mutation in the Rb protein
- the mutation leads to the loss of the inhibitory effect of Rb and allows uncontrolled cell division
What are key attributes of tumour suppressor genes ?
- familial cancer syndromes
- inactivation in common human cancers (loss of heterozygosity)
- recessive at a cellular level
- two-hit hypothesis
Describe loss of heterozygosity
- 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
Describe the two-hit hypothesis in regards to cancer
- at least 2 mutations are required for cancer
- a single mutation means there is potential for cancer formation
Describe how cell cycle checkpoints work
- 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
