Piano exercise sheets
associated with the plane rotation about the N--Cα bond. Ψ characterizes the conformation of the peptide plane at the carboxyl end of the Cα atom – this angle is associated with the peptide plane rotation about the Cα--C’ bond. (2) (5 pts) What groups are connected by the hydrogen bonds in the α-helix and in the β-sheet? The alpha helix (α-helix) is a common motif in the secondary structure of proteins and is a right hand-spiral conformation (i.e. helix) in which every backbone N−H group donates a hydrogen bond to the backbone C=O group of the amino acid located three or four residues earlier along the protein sequence. forms of beta sheet. The difference is in the relative direction of neighboring strands and in the way they hydrogen bond. Either way, just as an alpha helix, a beta sheet satisﬁes all hydrogen bonds of a peptide backbone. The only hydrogen bonds left un-bonded are those at the edges of the sheet. Beta sheets consist of beta strands (also β-strand) connected laterally by at least two or three backbone hydrogen bonds, forming a generally twisted, pleated sheet. A β-strand is a stretch of polypeptide chain typically 3 to 10 amino acids long with backbone in an extended conformation.