2. The likely regular conformations of protein molecules were proposed before they were actually observed! 2.1 This was accomplished by building precise molecular models 2.1.1 Experimental data(from X-ray studies) were closely adhered, interpreted. 2.1.2 Single bonds other than the peptide bond in the backbone chain are free to rotate
2. The likely regular conformations of protein molecules were proposed before they were actually observed! 2.1 This was accomplished by building precise molecular models. 2.1.1 Experimental data (from X-ray studies) were closely adhered, interpreted. 2.1.2 Single bonds other than the peptide bond in the backbone chain are free to rotate
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). 2.2.2R 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 1.5 a 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-) 2.2L 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)
C N O C C C N H R (c)
+180 120 60 60 -120 180 -180 +180 φ( degrees)