2.2. 4 The model made optimal use of internal hydrogen bonding for structure stabilization 2.2.5 Each carbonyl oxygen of the residue n is hydrogen bonded to the nh group of residue(n+4) 2.2.6 The residues forming one a-helix must all be one type of stereoisomers(either L-or D-) 2.2L amino acids can be used to build either right- or left-handed a-helices(the helix spiraling away clockwise or counterclockwise respectively).2.2.4 The model made optimal use of internal hydrogen bonding for structure stabilization. 2.2.5 Each carbonyl oxygen of the residue n is hydrogen bonded to the NH group of residue (n+4). 2.2.6 The residues forming one a-helix must all be one type of stereoisomers (either L- or D-). 2.2.7 L amino acids can be used to build either right- or left-handed a-helices (the helix spiraling away clockwise or counterclockwise respectively)