Tertiary Structure Fibrous and Globular Proteins

A segment of the pleated-sheet structure of 3-keratin. Adjacent chains run in opposite directions and are held together by hydrogen bonds (shown in color). R groups project above or below the mean plane of the sheet. 

We may well ask how materials as rigid as horses hoofs, as springy as hair, as soft as silk, as slippery and shapeless as egg white, as inert as cartilage, and as reactive as enzymes, can all be made of the same building blocks amino acids and proteins. The key lies mainly in the amino acid makeup itself. So far we have focused on the protein backbone and its shape. But what about the diverse R groups of the various amino acids How do they affect protein structure  

PROBLEM 17.20 Which amino acids in Table 17.1 have nonpolar R groups Highly polar groups Relatively flat R groups  

Fibrous proteins (including keratins, collagens, and silks) have rather rigid shapes and are not water soluble. 

Globular proteins (including enzymes, hormones, transport proteins, and storage proteins) are 

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