factors that influence cytochrome P450 expression are related to exposure to xenobiotics (drugs, food components, environmental chemicals) and some are genetically based. (i) If a person is a cigarette smoker, we would expect the expression of one isoform of cytochrome P450 in their liver will differ from its expression in a non-smoker. Explain why this is so, with mechanistic details of what cellular and molecular events cause the difference in expression of this cytochrome P450 isoform. (12 pt) (ii) A significant number of people get little or no pain relief when prescribed codeine, whereas most people find it an effective analgesic. Explain the likely differences in cytochrome P450 between the responders and nonresponders. (6 pt)