Question

Describe primary, secondary, tertiary, and quaternary structure and differentiate among the structures based on

• Stabilization by intramolecular covalent bonds
• Stabilization by hydrogen bonds
• Stabilization by hydrophobic effect
• Function in binding ligand
• Regulation of function by allostery

Answer 1

Solution

• Primary Structure of Proteins - stabilized by covalent interaction

  The primary structure is the sequence of amino acids that make up a polypeptide chain. 20 different amino acids are found in proteins. The exact order of the amino acids in a specific protein is the primary sequence for that protein.

  Secondary Structure of Proteins- stabilized by hydrogen bonding, ionic bonding-electrostatic interaction

  Protein secondary structure refers to regular, repeated patterns of folding of the protein backbone. The two most common folding patterns are the alpha helix and the beta sheet.
  Alpha Helix In an alpha helix, the polypeptide backbone coils around an imaginary helix axis in clockwise direction. In this illustration, only the N-C-CO backbone atoms are shown. Note the coiling of the backbone around an imaginary axis down the center of the helix.
  Beta sheet In the beta sheet secondary structure, the polypeptide backbone is nearly fully extended. The R-groups (not shown) are alternately pointed above and then below the extended backbone.

  Quaternary Structure of Proteins- are stabilized by hydrophobic interaction, hydrogen bonding

  Many proteins are formed from more than one polypeptide chain. The quaternary structure describes the way in which the different subunits are packed together to form the overall structure of the protein. For example, the human hemoglobin molecule shown below is made of four subunits.

• Tertiary Structure of Proteins- are stabilized by salt bridges, disulphide bonds.

  Tertiary structure refers to the overall folding of the entire polypeptide chain into a specific 3D shape. The tertiary structure of enzymes is often a compact, globular shape.