Peptide links are formed when two amino acids join together. This results in the loss of a water (H2
O) molecule and is called a condensation reaction.
Stages in the formation of peptide links 1. The COOH (acidic) group of one amino acid reacts with the NH2
(basic) group of another.
2. The COOH (acidic) group loses an OH group. The NH2
(basic) group loses a hydrogen
(H) atom.The hydrogen (H) atom and the OH group join together to form a water (H2 molecule that is lost.
O)
3. The result is a CO-NH bond. This new molecule is called a dipeptide (two amino acids joined together). When more than 20 amino acids join together, a polypeptide is formed. When more than 50 amino acids join together, a protein is formed. Each protein consists of one or more polypeptide chains.
The reverse of the condensation reaction is called hydrolysis. Hydrolysis involves the addition of water and enzyme action. It occurs during digestion, when proteins are broken down into individual amino acids.
? Give an account of protein and refer to how a peptide bond is formed. (8) HL
Structure of proteins Primary structure
• Primary structure is the order or sequence of amino acids in protein chains
• Amino acids can be arranged in many different combinations. Insulin, one of the simplest proteins, contains 51 amino acids.
