Compléter Cytochrome P450 EnzymesVersion en ligne Use this activity to revise this important family of enzymes! par Natalia Bilton 1 less breakdown DNA higher genes endoplasmic longer medications humans quickly toxins function medications polymorphism liver P450 sooner Enzymes produced from the cytochrome P450 genes are involved in the formation ( synthesis ) and breakdown ( metabolism ) of various molecules and chemicals within cells . Cytochrome enzymes metabolize external substances , such as that are ingested , and internal substances , such as that are formed within cells . There are approximately 60 cytochrome P450 genes in . Cytochrome P450 enzymes are primarily found in cells but are also located in cells throughout the body . Within cells , cytochrome P450 enzymes are located in the reticulum . The cytochrome P450 enzymes in the endoplasmic reticulum usually metabolize external substances , primarily and environmental pollutants . A is any difference in the nucleotide sequence between individuals . These differences can be single base pair changes , deletions , insertions , or even changes in the number of copies of a given sequence . Common variations ( polymorphisms ) in cytochrome P450 can affect the of the enzymes . The effects of polymorphisms are most prominently seen in the of medications . Depending on the gene and the polymorphism , drugs can be metabolized or slowly . If a cytochrome P450 enzyme metabolizes a drug slowly , the drug stays active and is needed to get the desired effect . A drug that is quickly metabolized is broken down and a dose might be needed to be effective .