lecture 4 - 4-1MCB354Lecture 4Reading in Lehninger:Chapter...

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Unformatted text preview: 4-1MCB354Lecture 4Reading in Lehninger:Chapter 4Secondary Structure of Proteins-helices-sheets-turnsBiological macromolecules are stabilized by interactions:StrongWeakCovalent bondsIonic interactionsIon-dipole interactionsVan der Waals interactionsHydrogen bondsHydrophobic interactions4-24-3Particularly stable arrangementsof residues giving rise toregular folding patternsof thepolypeptide backbone3-D foldingof a polypeptide:i) simple combinations of 2 structuralelements = motifsii) combination of motifs into domains Secondary structure of proteinsPeptide bond has partial double bond character4-4is 6% ofbonds w. Pro.unable to rotatefreelybecause ofpartial double bond characterrotation permittedabout N-Cand C-C bondsATOMS LIEIN PLANE4-5Peptide bond is rigid and planarThe Dihedral Angle4-6polypeptide in fully extended conformation with all peptide groups in the same plane:then, by convention, both and are defined as 180.N-Cbond angle C-C bond angle 4-7and anglesNot all and angles are allowed 4-8eg. if we try to rotate the bonds flanking Csuch that both and = 0, and the two peptidebonds flanking that -carbon are in the sameplane, it wont work, because of steric overlapbetween an carbonyl Oand an -amino HRamachandran plot4-9Fully allowed conformations,no steric overlapIN DARKEST BLUEConformations allowed at limitsfor unfavorable atomic contactsConformations permissible if a...
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lecture 4 - 4-1MCB354Lecture 4Reading in Lehninger:Chapter...

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