The enzyme classes
Grouped by the reaction they run, which is the order we will take them
Hydrolysis
water attacks; the bond is destroyed
- Endonucleases
- Exonucleases
- Phosphatases
Transphosphorylation
an alcohol attacks; the bond is moved
- DNA Polymerases
- RNA Polymerases
- Ligases
- Kinases
- Recombinases
Methyl transfer
a base attacks a methyl group: carbon this time, not phosphorus
So here is the shape of the rest of the lecture, and it is not an arbitrary list. The first three run the reaction you just watched with water: endonucleases, exonucleases, phosphatases. All hydrolysis, all destroying a bond. The next five run it with an alcohol: the two polymerases, ligases, kinases, recombinases. All transphosphorylation, all moving a bond rather than destroying it. And the third is the oddball, methyl transfer. Methyltransferases are not doing phosphorus chemistry at all: a nitrogen or a carbon on the base is the nucleophile, and what it attacks is the methyl on S-adenosylmethionine. Same idea, a nucleophile displacing a leaving group, on a completely different atom, which is why they come last and get their own drawing. If you remember one thing from this opening, make it which of the three an enzyme belongs to, because that tells you what it does to the bond. We will take them in that order.
The eight enzyme classes grouped by mechanism, in the order the lecture takes them. Hydrolysis, where water attacks and the bond is destroyed: endonucleases, exonucleases, phosphatases. Transphosphorylation, where an alcohol attacks and the bond is moved: DNA polymerases, RNA polymerases, ligases, kinases, recombinases. And neither: methyltransferases, which hand a methyl group to carbon rather than to phosphorus.