The linkage that joins amino acid units in a protein is

  • A. a glycosidic linkage
  • B. a peptide linkage, formed by condensation between a carboxyl and an amino group
  • C. an ester linkage
  • D. a hydrogen bond

Explanation

The carboxyl group of one amino acid condenses with the amino group of the next, releasing water and leaving a CO-NH amide link known as the peptide bond. Glycosidic links join sugars and ester links join glycerol to fatty acids, so each class of macromolecule has its own characteristic linkage. Hydrogen bonds are important in proteins but hold the chain in shape rather than joining the units.

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