CoA is composed of two main parts, a long protein-like chain (shown in black in the figure), joined to adenosine diphosphate, ADP, (shown in blue) which is one of the molecules (along with ATP) used for energy storage. The important part of the molecule is at the end of the protein chain, which terminates in a sulph-hydryl (-SH) group (red). This group is highly reactive, and links to carboxylic acid molecules via a thioester bond. The most important acid is acetic acid, and when it is joined to CoA, the resulting compound is known as acetyl-CoA.
Acetyl-CoA is also an important component in the biogenic synthesis of the neurotransmitter acetylcholine. Choline, in combination with acetyl-CoA, is catalyzed by the enzyme choline acetyltransferase to produce acetylcholine and a Coenzyme A byproduct.