![]() 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 #Bonds within a peptide backbone with free rotation pro#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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