Question

How do the four levels of protein structure affect the shape of enzymes and why is this important for enzyme function? Explain the "lock and key" model of enzyme function using the terms substrate, active site, and product.

Answer 1

The four levels of protein structure are primary, secondary, tertiary and quaternary structure. A chain of polypeptide made by amino acid defines the primary structure of protein. There are 20 different amino acid. A proteins can be acidic , basic or neutral based on the side chain of these amino acids hence it is important for its function. A primary structure of protein determine the other structure of proteins.

The local structure conformation due to hydrogen bonding form stretchs or strands defines the secondary structure of protein. There are two type of secondary structure- alpha helix and beta sheets. alpha helix is the right handed coil form in a polypeptide chain while beta sheet is due to hydrogen bond between the strands with the formation of sheet.

A tertiary structure of protein is the overall three dimensional structure of protein. The protein molecure with squeeze or bend or twist to become lowest energy to attain three dimensional structure. The overall function of the protein is determine by the three dimensional structure of protein.

Many functional proteins are made up of different polypeptide chain known as sub-units. These sub-units may be same ot homodimers or different hetero-dimers. A quaternary structure is the protein complex formed by different sub-units. The function of these protein is defined by the interaction of these sub-units.

The lock and key model of enzyme function defines that for every substrate structure there is an enzyme active site perfectly fits the substrate. I have given a diagram below.