For 10 points, name this functional group that is similar to a ketone.
In transaminases that use PLP as a cofactor, the amine attacks one of these functional groups before being transferred to the product. A common substrate analogue in enzyme inhibition replaces the C-terminus with one of these functional groups. Hydration of these compounds produces hemiacetals, and they produce a chemical shift from 9.5 to 10.5 ppm on proton NMR. Reacting these compounds with ammoniacal silver nitrate produces a silver mirror in the Tollens test. The simplest member of this group is often used as a preservative, and this functional group features a carbon atom double bonded to an oxygen atom and single bonded to an atom of hydrogen. For 10 points, name this functional group that is similar to a ketone.
In transaminases that use PLP as a cofactor, the amine attacks one of these functional groups before being transferred to the product.
{aldehydes}