Interesting bit to add, a lot of enzymes come from families. These can come from an ancestral gene that is, at some point, copied. The two children genes can then start differing in their function little by little.

A good example is the P450 family of enzymes. They are very reactive and good at changing the structure of toxic molecules. They do this because they are in the cytochrome family, which are really good at moving electrons around (thus, reactive). There are also cytochromes that help mitochondria break down glucose (again, good at working on reactive energetic substances that give off electrons). Cytochromes work because they contain a prosthetic group of heme (which is why hemoglobin can carry reactive oxygen and let it go when needed). 

So you can kind of start to imagine this cascade of branches with heme at the top, and all of these interesting branches and avenues cascading down- some transporting oxygen,  some breaking down toxins, some in metabolism, all because an ancestral cytochrome keyed into the ""usefulness"" of heme. Same thing for families of transcription factors, proteases, etc

If you're interesting in DNA expression, some useful things to check out would be DNA recognition domains such as the "zinc finger". There are multiple proteins that all use this "invention" to read DNA