It has been suggested that smoking, an epigenetic factor can lead to tumour growth and cancer. Use your knowledge of the epigenome and its structure to explain how this could occur. [5 marks]

Marking Scheme: MP1: Define epigenome- layers of chemical tags covering the DNA and histone protein complex MP2: Increased Methylation of DNA molecule MP3: enzymes attracted to complex/acetyl groups removed from histones MP4: histones become more positive and attract the negative DNA molecule more/ tightly packed complex MP5: transcription factors can no longer bind to DNA molecule/ transcription is ceased/ genes switched off MP6: less damaged DNA is repaired/ more mutations/ more abnormal body cells/ more tumour growth