Your best buddy is thoroughly confused when it comes to genetics. She is confused about what exactly a gene is and how is it expressed. She states 'how can it be that one of my muscle cells has the same genes as one of my nerve cells yet they have such different functions?'. Your friend needs help! Using E. coli as an example, explain to your friend why this bacterium sometimes, but not always, expresses its gene encoding nitrate reductase. Make sure you make the distinction between DNA and RNA so she won't be confused. Point out the importance of the 2' hydroxyl (OH) on RNA and why that's a gamechanger.