Biology A-level (Edexcel A) T3.4.13 - Cancer

DEFINE + EXPLAIN: cancer

cancer is uncotnrolled cell division

this is where the rate of cell multiplication is higher than the rate of cell deaths

this causes the growth of a tumour

EXPLAIN: the direct cause of cancer

cancer is caused by damage to DNA

DEFINE: oncogene

oncogenes are genes that code for proteins that stimulate transition of stages in cell division (this includes epigenetic changes)

EXPLAIN: how oncogenes controls cell division in the cell cycle

oncogenes produce proteins to continue or stop the cell cycle

these proteins inhibit or activate reactions in the next stage

this allows progression of the cell cycle to be controlled

EXPLAIN: how less methylation to oncogenes affects the cell cycle

less methylation means less DNA on oncogene is occupied with a methyl group

so more RNA polymerase can bind to DNA and transcription to mRNA can occur, making the oncogenes active

therefore allows the cell cycle to be continually active

this can lead to excessive division

DEFINE: tumour suppressor genes

tumour supressor genes produce supressor proteins that stop the cell cycle

EXPLAIN: how more methylation to tumour suppressor genes affect the cell cycle

more methylation to DNA in tumour supressor genes means more DNA is occupied with a methyl group

less RNA polymerase can bind to DNA and so transcription to mRNA cannot occur. This makes the tumour supressor genes inactive.

therefore allows the cell cycle to be more active

this can lead to excessive division

EXPLAIN: the role of the p53 protein

p53 inhibits enzymes in G1/S phase

this means they prevent cells from copying DNA

LIST: environmental factors of cancer

1) Tar from smoking - lodges in bronchi and damages surrounding epithelial cells

2) UV exposure - damages skin cells

3) Diet - antioxidants destroys radicals which damage DNA