2.2 The simplest arrangement of the polypeptide chain was proposed to be a helical structure called a-helix (Pauling and corey, 1951) 2.2.1 The polypeptide backbone is tightly wound around the long axis (rodlike). 2.2R groups protrude outward from the helical backbone 2.2.3 A single turn of the helix(corresponding to the repeating unit in a-keratin) extends about 5.6 Angstroms, including 3. 6 residues(each residue arises 1.5a and rotate 100 degrees about the helix axis)
2.2 The simplest arrangement of the polypeptide chain was proposed to be a helical structure called a-helix (Pauling and Corey, 1951) 2.2.1 The polypeptide backbone is tightly wound around the long axis (rodlike). 2.2.2 R groups protrude outward from the helical backbone. 2.2.3 A single turn of the helix (corresponding to the repeating unit in a-keratin) extends about 5.6 Angstroms, including 3.6 residues (each residue arises 1.5 Å and rotate 100 degrees about the helix axis)
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./L 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)
Carbon Amino terminus Hyd Oxygen NItrogen ORgroup 42 ,4A 003 (3.6 residues) G 4 Carboxyl terminus a (b
c)
(d)