Answers to all problems are at the end of this book. Detailed solutions are available in the Student Solutions Manual, Study Guide, and Problems Book.
Determining the Length of a Keratin Molecule The central rod domain of a keratin protein is approximately 312 residues in length. What is the length (in A) of the keratin rod domain? If this same peptide segment were a true α-helix how long would it be? If the same segment were a β-sheet, what would its length be?
To Determine: The length of the keratin rod domain should be determined along with the length of the peptide segment when the same peptide segment were a true a helix. Length of the segment should be determined when the same segment were a ß sheet.
Introduction: One turn of a helix represents 3.6 amino acid residues. For true a helix, each amino acid residue extends 1.5 oA along the axis of the helix. So, the length of one turn is 3.6×1.5 oA= 5.4 oA . This is referred to as the pitch of the helix. But keratin protein has a distorted alpha-helix with a pitch length of 5.1 oA
Beta sheet structure can be pictured as a twofold helix with two residues per turn. The distance between residues in the anti-parallel pleated sheet is 3.47 oA and 3.25 oA in the parallel pleated sheet.
Explanation of Solution
The length of the keratin rod domain = 5.1 oA1 turn×1 turn3.6 residues×312 residues = 442 oA
If the segment were a true helix = 5.4 oA1 turn×1 turn3.6 residues×312 residues = 468 oA
If the segment were an antiparallel beta-sheet = 3.47 oA × 312 residues = 1083 oA
If the segment were a parallel beta-sheet = 3.25 oA × 312 residues = 1014 oA
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- BiochemistryBiochemistryISBN:9781305577206Author:Reginald H. Garrett, Charles M. GrishamPublisher:Cengage Learning