structure of the protein molecule being studied for over 200 years.She is known for many proteins.Some of them have been synthesized (e.g., insulin, RNase).The basic structural and functional unit of the protein molecule are amino acids.Furthermore carboxyl and amino groups of proteins also contain other functional groups, which determine their properties.Such groups include arranged in a side chain of the protein molecule: carboxy group of aspartic acid or glutamic acid, amino group of lysine or hydroxylysine, guanidine group of arginine, histidine imidazole group, the hydroxyl group of serine and threonine, a phenol group of tyrosine, the sulfhydryl group of cysteine, disulfide group cystinethioether group of the methionine, phenylalanine benzelnoe core aliphatic chains of other amino acids.
There are four levels of the structural organization of the protein molecules.
primary structure of the protein.Amino acids in the protein molecule are joined together by peptide bonds, thus forming the primary structure.It depends on the qualitative composition of the amino acid sequence of their numbers and interconnect.The primary structure of the protein most often determined by Sanger.Was treated with a solution of the target protein ditroftorbenzola (DNP), thereby forming a protein-dinitrophenyl (DNP-protein).Subsequently DNP-hydrolyzed protein, the residue of a protein molecule produced and DNP-amino acid.DNP-amino acid is isolated from the mixture and to hydrolysis.Hydrolysis products are amino acids and dinitrobenzene.The residue of the protein molecule react with new portions DNP until until the whole molecule does not fall apart on the amino acid.Based on the quantitative study of amino acids make up the primary structure of the scheme of the individual protein.Known primary structure of the protein insulin, myoglobin, hemoglobin, glucagon and many others).
By Edman degradation protein is treated with phenyl isothiocyanate.Sometimes use proteolytic enzymes - trypsin, pepsin, chymotrypsin, peptidases, etc.
protein secondary structure.American scientists using X-ray analysis and found that the protein polypeptide chain often exists in the form of alpha-helices and sometimes beta structures.
alpha helix compared with a spiral staircase, which perform the function of the degrees of amino acid residues.In the molecules of fibrous proteins (silk fibroin) polypeptide chains is almost fully extended (beta-structure) and placed in the form of spheres, stabilized by hydrogen bonds.
alpha-helix can be formed spontaneously in the synthetic polypeptides (dederon, nylon), which have a molecular weight of from 10 to 20 thousand. Yes.In certain parts of the protein molecules (insulin, hemoglobin, RNase) violated alpha-helical configuration of the peptide chain, and formed spiral structure of another type.
tertiary structure of the protein.Spiral-shaped portions of the polypeptide chain of the protein molecule are in different relationships, which determine tertiary (three-dimensional) structure, form a volume and shape of the protein molecule.It is believed that the tertiary structure of automatic and occurs due to the interaction of the amino acid radicals with the solvent molecules.Wherein the hydrophobic radicals are "drawn" into the protein molecules to form their dry areas and hydrophilic groups are oriented towards the solvent, which causes the formation of energetically favorable confirmations molecule.This process is accompanied by the formation of intramolecular bonds.The tertiary structure of the protein molecule transcribed to RNA-ase, hemoglobin, lysozyme egg.
quaternary structure of protein.This type of structure of the protein molecules is the result of association of several subunits integrated into a single molecule.Each subunit has a primary, secondary, and tertiary structures.
