Chapter 21, Problem 16A

Interpretation Introduction

Interpretation: Function of the amino acid cysteine in influencing the tertiary structure of a protein needs to be explained.

Concept Introduction:

Cysteine is an amino acid with sulfur atom in the side chain. It has a basic physical role. It is an alpha-amino acid, polar amino acid and amino acid-containing sulfur.

Explanation of Solution

Disulfide bridges, the covalent bonds formed between two cysteine residues, further strengthen the protein shape. Disulfide bridges are formed when the hydraulics groups of two cysteine residues come into close contact due to protein folding. Covalent bonds are not weak interactions. The tertiary structure is the functional structure of polypeptide chains. Each protein has a specific three-dimensional shape which exhibits functional groups on its outer surface and allows it to interact with the other molecules and give it its unique function.

Because there is a reactive group at its side chain, this keeps cysteine in a special state that cannot be replaced or substituted with other amino acids. This is because sulfide bridges formed by cysteine residues are a permanent component of the protein primary structure.