Elementary plant Biochemistry and Biotechnology (2+1)

Quaternary structure

• Proteins that have more than one subunit or polypeptide chains will exhibit quaternary structure.
• Quaternary structure refers to a functional protein aggregate (organization) formed by interpolypeptide linkage of subunits or polypeptide chains.
  
• These subunits are held together by noncovalent surface interaction between the polar side chains.
• Proteins formed like above are termed oligomers and the individual.
• Polypeptide chains are variously termed protomers, monomers or subunits.
• The most common oligomeric proteins contain two or four protomers and are termed dimers or tetramers, respectively.



• Myoglobin has no quaternary structure since, it is composed of a single polypeptide chain.
  
• Hemoglobin molecule, which consists of four separate polypeptide chains, exhibits quaternary structure.
• The ribbon parts represent the protein globin; the four green parts are the heme groups.
• Quaternary structure may influence the activity of enzymes . Some enzymes are active only in their quaternary state and become inactive when split into smaller units.
• Other enzymes are inactive in the quaternary state and are activated only when they are dissociated to form monomeric state