Answer
$(a)$ Bends are most likely at residues 7 and 19; Pro residues in the cis configuration accommodate turns well.
$(b)$ The cys residues at positions 13 and 24 can form a disulfide bond.
$(c)$ External surface; polar and charged residues (Asp,Glu,Lys); interior; nonpolar and aliphatic residues (Ala,lle); Thr, though polar, has a hydropathy index near zero and thus can be found either on the external surface or in the interior of the protein.
Work Step by Step
7 is the minimum number of amino acid residues necessary for one segment of helix to traverse the membrane completely.
