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.
