proteins

Proteins are structurally and functionally complex molecules.The term protein is used to describe a three-dimensional structure formed by folding one or more polypeptides.They show four levels of structural organization, with polypeptides as the main structure.Proteins have secondary structure when polypeptide chains are folded into alpha helix and beta.The tertiary structure of the protein constitutes the complete three-dimensional structure of the polypeptide chain.When more than one polypeptide chain is involved in a protein complex, the protein structure is designated as quaternary ammonium.Polypeptide chain folding to form proteins is based on the formation of many weak non-covalent bonds between different parts of a chain or even two or more polypeptide chains.Non-covalent bonds involve atoms of the main polypeptide chain and side chain R groups, and have three types: hydrogen bonds, ionic bonds and van der Waals bonds.A large number of weak noncovalent bonds operate in parallel and their strength binds to ensure the stability of the folded protein structure.The substructure of protein tissue is protein domain.It consists of any part of a polypeptide chain that can be independently folded into a stable structure.Each domain contains 40 to 350 amino acids.The smallest proteins present a single domain, while large proteins may contain as many as dozens of domains.Each domain of a protein is usually associated with a different function.The functional properties of proteins depend largely on their structure and shape, enabling them to interact with other molecular physics.These interactions are always specific and selective.Each protein can bind to one or more molecules called ligands with a high affinity to its ligand binding site.Ligand binding sites are cavities on the surface of proteins formed by folding polypeptide chains.Individual ligand-binding sites in proteins can bind to different ligands, regulate protein function, or help move proteins to specific sites in cells.Protein function is closely related to its structure.Changes in an amino acid can destroy its shape and result in loss of function.