Chapter 5 The Three-dimensional Structure of proteins
Chapter 5 The Three-dimensional Structure of Proteins
1. Early studies on the peptide(protein) structure 1.1 The peptide(o=c-n-h) bond was found to be shorter than the c-n bond in a simple amine and atoms attached are coplanar 1.1.1 This was revealed by X-ray diffraction studies of amino acids and of simple dipeptides and tripeptides. 1.1.2 The peptide(amide) bond was c-N double bond, 1.27) thus having partiar'< found to be about 1. A(C-N single bond, 1.49; double bond feature(should be rigid and unable to rotate freely)
1. Early studies on the peptide (protein) structure 1.1 The peptide (O=C-N-H) bond was found to be shorter than the C-N bond in a simple amine and atoms attached are coplanar. 1.1.1 This was revealed by X-ray diffraction studies of amino acids and of simple dipeptides and tripeptides. 1.1.2 The peptide (amide) bond was found to be about 1.32 Å (C-N single bond, 1.49; C=N double bond, 1.27), thus having partial double bond feature (should be rigid and unable to rotate freely)
1.3 The partial double bond feature is a result of partial sharing(resonance)of electrons between the carbonyl oxygen and amide nitrogen 1.1.4 The atoms attached to the peptide bond are coplanar with the oxygen and hydrogen atom in trans positions. 1.2 X-ray studies of a-keratin(the fibrous protein ma king up hair and wool) revealed a repeating unit of 5.4 A(Astury in the 1930s)
1.1.3 The partial double bond feature is a result of partial sharing (resonance) of electrons between the carbonyl oxygen and amide nitrogen. 1.1.4 The atoms attached to the peptide bond are coplanar with the oxygen and hydrogen atom in trans positions. 1.2 X-ray studies of a-keratin (the fibrous protein making up hair and wool) revealed a repeating unit of 5.4 Å (Astury in the 1930s)
The carbonyl oxygen has a partial negative charge and the amide nitrogen a partial positive charge, setting up a small electric dipole. Virtually all peptide bonds in proteins occur in this trans configuration; an exception is noted in Igure 6-8b F O O H H H
Carboxyl 124A terminus 1.53AC 146A 132A Amin terminus H (b)