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Explain the structure of proteins. |
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Answer» Solution : The structure and shape of proteins can be studied at FOUR different levels called primary, secondary, tertiary and quaternary. Each level is more complex than the previous one. (1) Primary structure : In primary structure, proteins contain polypeptide chain. Each PROTEIN has amino acids linked with each other in a SPECIFIC sequence and this sequence of amino acids is termet as primary structure. Any change in the primary structures creates different protein molecule. (2) Secondary structure : When long amino acid chain is coiled, looped or folded, it gives particular shape to a protein molecule, it is referred as secondary structure. There are two differet types of structures`alpha`helix and `beta` - pleatedsheets .  (i) `alpha`-Helix structure : In`beta`- Helix structure a polypeptide chain gets coiled by twisting into right handed spiral known as `alpha` -helix. The hydrogen bonding between`-overset(|)(C) =O` and -NH GROUPS occursin differentparts of the samechainresultingin foldingof polypeptide chain. (ii) `beta`- pleatedstructure: The polypeptide chain lie side by side and are held together by intermolecular hydrogen bonding. The poly peptide chains are stretched out resulting in a flat sheet. The contraction results in a pleated sheets called `beta`-pleated sheet.   (3) Tertiary structure : The secondary structure on folding givesriseto molecularshapesi.e.,fibrousandglobular . Thepolypeptide intertiarystrcuture heldby disulphideor hydrogenbondsor van derWaalsforcesor electrostaticforces ofattraction. (4)Quaternary structure : Two ormore AMINOACIDS chainsor polypeptidechains forms complexprotein. Thespatialarrangement ofthesepolypeptidechains withrespect to eachotheris knowas quaternary structure . |
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