CHAPTER 1 FOOD SCIENCE AND NUTRITION HL Secondary structure
• Secondary structure involves the folding of the primary structure of proteins into definite shapes
• Polypeptide chains either fold in on themselves or cross-link with another polypeptide chain. This causes the chains to form a spiral shape. Cross-links give proteins their unique properties, e.g. gluten its elasticity
• There are two main types of cross-links: disulfide bonds and hydrogen bonds Disulfide bonds
Hydrogen bonds
• Disulfide bonds occur when two sulfurs from two amino acids join together from either a single polypeptide chain or two different polypeptide chains
• The amino acid cysteine contains sulfur. Two cysteine amino acids can form a disulfide bond.
• Insulin contains disulfide bonds
• Hydrogen bonds occur when a hydrogen (H) from the N-H group of one amino acid and an oxygen (O) from the C=O group of another amino acid join together from either a single polypeptide chain or two different polypeptide chains
• The amino acids serine and tyrosine are capable of forming hydrogen bonds
• Collagen contains hydrogen bonds
? Explain what is meant by primary protein structure. (2) OL Describe (i) the primary structure and (ii) the secondary structure of protein. (24) HL
