![]() Parallel sheets have strands that are oriented in the same directionĪntiparallel sheets have strands that are oriented in opposite directions O Two major orientations of B- Sheets are determined by the directionality Of the strands within: # o Sheets are held together by the hydrogen bonding of amide and carbonyl groups of the peptide bond from O Multi B- strand interactions are called sheets O Sheet like arrangement of the backbone is held together by hydrogen bonds between the backbone amides O The planarity of the peptide bond and tetrahedral geometry of the a- Carbon create a pleated sheet - like O Negatively charged residues often occur near the Positive end of the helix dipole # o The A- helix has a large macroscopic dipole moment that is enhanced by unpaired Amides and carbonyls ° All peptide bonds in the a- helix have a similar orientation O Recall that the peptide bond has a strong dipole moment Attractive or repulsive interactions between side chains 3 to 4 amino acids apart will affect formation.O Gly acts as a helix breaker because the tiny R group supports other conformations O Pro acts as a helix breaker because the rotation around the N - Ca ( 4- angle) bond is impossible # o small hydrophobic residues such as Ala and Leu are strong helix formers O Not an polypeptide sequences adopt a- helical structures Y lpsi) : angle Around the a- carbon - carbonyl carbon bond Sequence Affects Helix Stability The Helix Dipole β-Sheets Parallel and Antiparallel β Sheets O Rotation around bonds connected to the a- Carbon is permitted f- / phil : angle around the a- carbon - amide nitrogen bond ° Rotation around the peptide bond is not permitted due to resonance structure # to exhibit a larger dipole moment in the favored trans configuration To be less reactive compared with esters, for example O The resonance causes the peptide bonds : O The peptide bond is a resonance hybrid of two canonical structures O The structure of the protein is partially dictated by the properties of the peptide bond Salt bridges ,Įspecially those buried in the hydrophobic environment, strongly stabilize the protein O Electrostatic Interactions - long range strong interactions between permanently charged groups. # ° London Dispersion - Medium range weak attraction between all atoms contributes significantly to the stability # o Hydrogen Bonds - Interaction of N - H and 0=0 Of the peptide bond leads to local regular structures such as O Hydrophobic Effect - the release of water molecules fromthe structured solvation layer around the moleculeĪs protein folds increases the net entropy ![]() There is an entropy cost to folding the protein into one specific native told.The native fold has a large number of favorable interactions within the Protein.This structure is called the native told.# ° This structure is able to fulfill a specific biological function Protein molecules adopt a specific three - dimensional conformation Chapter 4: 3D Structure of Protein Structure of Proteins Favourable Interactions in Proteins Primary Structure: The Peptide Bond The Rigid Peptide Plane and the Partially Free Rotations ![]()
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