- Carcinogens (agents which can cause cancer):
- e.g.: smoke, radiation;
- cause mutations in genes which control cell division (oncogenes);
- divide uncontrollably → small mass of cells (tumour);
- Tumour cells do not respond to signals from nerves and hormons:
- continue to grow;
- no programmed cell death occurs (apoptosis);
- benign → does not spread from origin (not cancerous);
- malignant → cancerous
- spread, invade and destroy other tissues;
- cells can break off from primary malignant tumour;
- spread via lympathic system;
- cause secondary tumours (metastasis) → hard to find + remove
- Cancers may take years to develop with few/no symptoms (→ but some symptoms are: haemoptysis (coughing up blood), pneumonia).
- usually advanced when discovered
Genes & Cancer
- Tendency to develop cancers seems to be inherited.
- Tumours cells in some cancers have abnormal chromosomes.
- Positive correlation between mutations and carcinogens.
- Oncogenes (genes that turn cells into cancers):
- → found when proto-oncogenes (normal versions of genes) mutate + become over-active.
- RAS Oncogenes:
- G-proteins are found on plasma membranes + enable cells to respond to growth factors;
- activated by enzymes within cell (GTPase);
- mutation of RAS gene → GTPase deficient proteins;
- mutated G-proteins remain active for longer → causing tumours;
- Myc Oncogenes:
- myc gene produces a protein needed for normal cell division;
- common mutation switches myc proto-oncogene from chromosome 8 to 14;
- there, acts as oncogene/abnormal cell division/tumour;
- when both myc and RAS oncogenes present together → malignant cells result;
Tumour Suppressor Genes
- Tumour suppressor genes:
- reduce normal activity by inhibiting cell division;
- initiate cell death (apoptosis) if the cell's DNA is damaged (due to mutations);
- mutations of this gene → loss of function ⇒ reults in tumours