1. Peptide linkage: Proteins are condensation polymers of α - amino acids in which the same or different α - amino acids are connected by peptide bonds. Chemically, a peptide bond is an amide linkage formed between – COOH group of one a – amino acid and – NH2 group of the other α - amino acid by loss of a molecule of water. Example
2. Primary structure: Proteins may contain one or more polypeptide chains. Each polypeptide chains has a large number of α – amino acids which are linked to one another in a specific sequence. The specific sequence in which the various α – amino acids present in a protein are linked to one another is called its primary structure. Any change in the sequence of α – amino acids creates a different protein.
3. Denaturation: Each protein in the biological system has a unique 3-D structure and has specific biological activity. This is called the native form of the protein. When a protein in its native form is subjected to physical changes like change in temperature, pH etc. hydrogen bonds are broken. Due to the cleavage of hydrogen bonds, unfolding of the protein molecule takes place and it looses its biological activity.
This loss of biological activity is called Denaturation. During denaturation 2° and 3° structures are destroyed but 1° structure remains intact. As a result of denaturation, globules proteins are converted into fibrous proteins. In other words denaturation leads to coagulation. That is why coagulated proteins are called denaturated proteins. Example boiling of egg causes coagulation of egg white.
