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Hair Versus Silk. The a-keratin of human hair is a good example of a fibrous protein with extensive a-helical structure. Silk fibroin is also a fibrous protein, but it consists primarily of b-sheet structure. Fibroin is essentially a
(a) If you were able to grab onto both ends of an α-keratin polypeptide and pull, you would find it to be both extensible (it can be stretched to about twice its length in moist heat) and elastic (when you let go, it will return to its normal length). In contrast, a fibroin polypeptide has essentially no extensibility, and it has great resistance to breaking. Explain these differences.
(b) Can you suggest why fibroin assumes a pleated sheet structure, whereas α-keratin exists as an α helix and even reverts spontaneously to a helical shape when it has been stretched artificially?
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Chapter 3 Solutions
Becker's World of the Cell (9th Edition)
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- Ala-Arg-Val-His-Asp-Gln Given the polypeptide chain above Estimate the net charge of the polypeptide chain at physiological pH (7.4) and at pH 5.0 . How many peptide bonds are there? What kind of polypeptide is it?arrow_forwardIn α-helices - what is the length of the hydrogen bonds between: TYR41H and GLU37O ALA39H and MET35O GLU38H and ILE34O THR36H and ARG32O. ARG32H and TYR28Oarrow_forwardRotation about the peptide bond in glycylalanine is hindered. Draw the resonance forms of the peptide bond and explain why.arrow_forward
- Instruction for the said activity: Write the structure of each of the following peptide at pH7 and identify how many peptide bond in each number. d. Alanyl-phenylalanine- aspartate- cysteine e. Threonyl- Isoleucyl-methionyl- leucine f. Lysyl-alanine -Phenylalanyl-tyrosyl- serinearrow_forwardwool consists of alpha keratin, pure wool sweaters exposed to hot water shrink alarmingly, after shrinkage, it is virtually impossible to stretch the seweater back to its original shape, what do you think is the biochemical cause of this phenomenon?arrow_forwardChoices: -cerebroside -monoglycosyl ceramide -glycosphingolipid -all are correctarrow_forward
BiochemistryBiochemistryISBN:9781305577206Author:Reginald H. Garrett, Charles M. GrishamPublisher:Cengage Learning