Structure of Protein

A protein is synthesised on the ribosome as a linear sequence of amino acids joined by peptide bonds. After synthesis, this raw chain undergoes a conformational change, folding into a specific three-dimensional shape required for it to function properly. Protein folding is described in terms of four successive levels of organisation. Primary structure is simply the linear order of amino acids along the polypeptide chain - the sequence itself. Secondary structure arises when functional groups exposed on the chain's surface interact with each other through hydrogen bonding, causing the chain to twist into a regular coiled shape called an alpha-helix, or to fold back on itself into a flat, pleated arrangement called a beta-pleated sheet. Tertiary structure arises when a secondary-structure-containing chain folds further into an overall compact, globular three-dimensional shape, often organised into distinct sub-regions called domains. Quaternary structure applies only to proteins built from more than one polypeptide chain: several folded polypeptide subunits assemble together into one larger, functional multi-unit protein, called a multimer, with each individual chain referred to as a subunit. For example, enzymes (which act as no …