Lehninger Principles of Biochemistry 6th Edition

Published by W.H. Freeman
ISBN 10: 1-42923-414-8
ISBN 13: 978-1-42923-414-6

Chapter 4 - The Three-Dimensional Structure of Proteins - Problems: 2

Answer

a) What Astbury didn't know then is that wool is a made of a fibrous protein called alpha-keratin. b) Unlike wool, silk is made of fibrin proteins which is always in the beta-sheet conformation.

Work Step by Step

a) 1) Alpha-keratin is made up of alpha-helices which repeat every 5.2A$ ^{\circ}$. This is the proteins secondary structure. 2) When the protein undergoes steaming and stretching, energy is introduced into the protein and a new repeating secondary structure appears. This time the secondary polypeptide structure repeats every 7$ ^{\circ}$. 3) Secondary structures repeating every 7$ ^{\circ}$ is characteristic of an antiparallel beta-sheet which is another type of secondary polypeptide structure. 4) The wool's protein is left to cool which shrinks the secondary polypeptide structure back into its original alpha-helices repeating every 5.2 $ ^{\circ}$ b) Introducing heat and energy to silk will not change its secondary protein structure and thus silk material won't shrink in the dryer.
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