Proteins are complex macromolecules essential for numerous biological functions. They are composed of amino acids linked by peptide bonds, forming polypeptide chains that fold into specific three-dimensional structures. The 20 amino acids that comprise proteins include alanine, arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, tryptophan, tyrosine, and valine. The linear sequence of amino acids (the primary structure of the protein) in a polypeptide chain, determining the protein's identity and properties. The primary structure of a protein (amino acid sequence) drives the folding and intramolecular bonding of the linear amino acid chain, which ultimately determines the protein's unique three-dimensional shape. Hydrogen bonding between amino groups and carboxyl groups in neighboring regions of the protein chain sometimes causes certain patterns of folding to occur. Known as alpha helices and beta sheets, these stable folding patterns make up the secondary structure of a protein. Most proteins contain multiple helices and sheets, in addition to other less common patterns. The ensemble of formations and folds in a single linear chain of amino acids, sometimes called a polypeptide, constitutes the tertiary structure of a protein. The quaternary structure of a protein refers to those macromolecules with multiple polypeptide chains or subunits. Proteins are dynamic and versatile molecules whose function and behavior can be understood through various biophysical principles and techniques. This integrated approach provides a comprehensive understanding of their roles in biology and their potential as targets for therapeutic intervention.
