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Explainaboutthe structure of proteins. |
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Answer» Solution :(i) Protein are polymersof amino acids. Their three dimensional structure dependsmainlyon thesequenceof aminoacids . Theprotein structurecan bedescribed at fourhierarchal levels called primary secondary , tertiaryandquatenarystructures . Primary structure of proteins: - Protein arepolypeptidechains made upof amino acidsconnected through peptidebonds. The relativearrangementof theaminoacidsin thepolypeptide chain is calledthe primarystructureof the protein.  Secondarystructureof proteins :The aminoacidsin the polypeptidechainforms highlyregularshapes through bondbetweenthe carbonyloxygen and theneighobouringaminehydrogen of themainchain. `alpha` - Helix and `beta` - strands or sheets are twomostcommonsubstructureformed byproteins. `alpha` - Helix: - In the `alpha`sub - structuretheamino acidsarearrangend in a righthanded helical (sprial) structure andare stabilisedby thehydrogen bond. The sidechains of the residues protrudeoutsideof thehelxi. Each turn of an `alpha` - helix containsabout 3.6 resisdues and is about5.4 long. `beta` - Strands :-Strands areextended extended peptidechainrather thancoiled. The hydrogen bond occur betweenmain chain carbonyl group one suchstrandand theamino group ofthe adjacentstrandresultingin thefromationof a SHEET likestructure . Thisarrangement is called `beta` - sheets. TERTIARYSTRUCTURE : The secondarystructure element (`alpha` - helix& `beta` - sheets ) further foldsto forma three dimensional arragement . Thistertiary structureof proteins are stabilised bythe interactions between the sidechains of theaminoo acids. These interactions INCLUDE thedisulphdebridgesbetween cysteine residues, electrostatic ,hydrophobic , hydrogenbondsand van der Waalsinteractions. Quaternay Structure : Theoxygen transportingprtotein ,haemoglobin CONTAINS fourpolypeptide chains whileDNA POLYMERASE enzyme that makecopies of DNA, has tenpolypeptidechains. In theseproteins the individual polypeptidechainsinteracts witheachother to form the multimericstructure whihcknowas quaternarystructure. Theinteractionsthatstabilises the tertiarystructures alsostabilised thequaternarystructures. |
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