Write a brief remark on protein main structure.

Biomolecules:

• The organic molecules which are produced in or by the living organisms are termed biomolecules.
• A protein is an exceedingly complex natural molecule made up of amino acid residues linked by peptide bonds.
• Proteins are found in all living species and contain a variety of biologically important molecules such as enzymes, hormones, and antibodies.

Primary Structure of Protein:

• Because of their partly double-bond character, peptide $-\mathrm{C}=\mathrm{N}-$ bonds are unable to rotate freely. As a result, the six atoms of the peptide bond are in a single plane, with the carbonyl group's oxygen atom and the amide nitrogen's hydrogen atom trans to each other.
• The structure of a peptide bond is stiff and flat.
• The polypeptide chain is made up of a sequence of rigid planes, each of which has a common point of rotation at $-\mathrm{C}$.
• The bond angles resulting from rotations are labeled (phi) for the $\mathrm{N}-\mathrm{C}$ bond and (psi) for the $\mathrm{C}-\mathrm{C}$ bond, according to the convention.