proteinstructure



		PROTEIN STRUCTURE

	Proteins are an important class of biological macromolecules present in all biological organisms, made up of such elements as carbon, hydrogen, nitrogen, phosphorus, oxygen, and sulfur. All proteins are polymers of amino acids. The polymers, also known as polypeptides consist of a sequence of 20 different L-?-amino acids. To be able to perform their biological function, proteins fold into one, or more, specific spatial conformations, driven by a number of noncovalent interactions such as hydrogen bonding, ionic interactions, Van der Waals' forces and hydrophobic packing.
				In order to understand the functions of proteins at a molecular level, it is often necessary to determine the three dimensional structure of proteins.


A number of residues are necessary to perform a particular biochemical function, and around 40-50 residues appears to be the lower limit for a functional domain size. Protein sizes range from this lower limit to several thousand residues in multi-functional or structural proteins.

			* Primary structure - the amino acid sequence of the peptide chains. * Secondary structure - highly regular sub-structures (alpha helix and strands of beta sheet) which are locally defined, meaning that there can be many different secondary motifs present in one single protein molecule. * Tertiary structure - three-dimensional structure of a single protein molecule; a spatial arrangement of the secondary structures. It also describes the completely folded and compacted polypeptide chain. * Quaternary structure - complex of several protein molecules or polypeptide chains, usually called protein subunits in this context, which function as part of the larger assembly or protein complex.

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