Protein Structure Essay

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Proteins are polymers which is set up by 19 different α-amino acids and one imino acid (Proline) linked by amida bond or peptide bond. A protein usually contain amino acid residues, covalently linked, which spontaneously form a three-dimensional structure, based on the self-recognition of its respective sequence. Covalent bonds (peptide and disulfide), hydrogen bonds, electrostatic interactions, hydrophobic interactions, and weak, nonspecific attractive and repulsive forces are kind of physical forces which related to protein structure. The component of amino acid may be distinguished based on chemical nature of side chain group at the α-carbon atom. The side chain group determine the physicochemical properties, such as solubility, charge and chemical reactivity. Aliphatic (Ala, Ile, Lue, Met, Pro, and Val) and aromatic (Phe, Trp, and Tyr) side chain are nonpolar. Thereby, it is cause less soluble in the water. In contrast to amino acid with charges (Arg, Lys, his, Glu, and Asp) and un-charge (Ser, Thr, Asn, gln, and Cys) side chains which are more soluble in the water. The relative number of basic (Arg, lys, and His) and acidic (Glu and Asp) amino acid residue in the protein may determine the net charge of a protein at any pH.
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It is the arrangement of multiple folded protein subunits in a multi-subunit complex. It includes set up structure from simple dimers to large homo-oligomers and complexes with defined or variable numbers of subunits. Protein quaternary structures are produced by the association of separate folded polypeptides (subunits) into an aggregate multimeric structure, under specified conditions of pH and temperature and without regard to the internal geometry of subunits. Alteration of quaternary structure of a protein denotes that subunits move relative to each other, which is affect to alterations of the physicochemical

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