The amide bond between amino acids is the basis of proteins.
Tips
usage
Pure chemistry term — you'll only meet it in compounds like 乙酰 (yǐxiān, acetyl), 酰胺 (xiān'àn, amide), or 酰基 (xiānjī, acyl group). Older texts use 醯 instead.
mistakes
Pronounced xiān, not xī. The 1st-tone reading trips up native speakers too because the 山 component looks like it could be a phonetic — it isn't.
