Biomolecules - Proteins (Amino Acids and Peptide Bond)

Amino acids are the building blocks of proteins, containing both an amino ($-NH_2$) and a carboxyl ($-COOH$) functional group. In $\alpha$-amino acids, both groups are attached to the same carbon atom.

Zwitterion formation: In aqueous solution, the carboxyl group loses a proton and the amino group accepts one, forming a dipolar ion known as a Zwitterion. In this state, amino acids show amphoteric behavior.

Classification: Amino acids are classified as Essential (must be obtained from diet, e.g., Valine, Leucine) and Non-essential (synthesized by the body, e.g., Glycine, Alanine).

Peptide Bond: A peptide bond is an amide linkage ($-CO-NH-$) formed between the $-COOH$ group of one amino acid and the $-NH_2$ group of another, with the elimination of a water molecule ($H_2O$).

Primary Structure: Refers to the specific sequence of amino acids in a polypeptide chain. Any change in this sequence creates a different protein.

Secondary Structure: Refers to the shape in which a long polypeptide chain exists, specifically the $\alpha$-helix and $\beta$-pleated sheet structures, stabilized by hydrogen bonding.

Tertiary Structure: Represents the overall folding of the polypeptide chains, resulting in Fibrous or Globular molecular shapes. It is stabilized by $H$-bonds, disulfide linkages, van der Waals forces, and electrostatic attractions.

Denaturation: When a protein is subjected to physical changes (like temperature) or chemical changes (like $pH$), the hydrogen bonds are disturbed, and the protein loses its biological activity. Only the primary structure remains intact.