The lipid portion of a typical bilayer is about 30 å thick. a) calculate the minimum number of residues in an α-helix required to span this distance. b) calculate the minimum number of residues in a β-strand required to span this distance. c) calculate the minimum number of residues in a β-strand required to span this distance if the strand axis is at 45° from the normal to the membrane d) explain why α-helices are most commonly observed in transmembrane protein sequences when the distance from one side of a membrane to the other can be spanned by significantly fewer amino acids than in a β strand orientation

a)The minimum number of residues in alfa helix to span 30 Å, is 20 residues

b)The minimum number of residues in a Beta sheet to span 30 Å, is 8.6 residues.

c) Should be better if you show an image to do this question.

d) Look answer below.

Explanation:

a) Due to every 5,4 Å there are 3,6 residues. So doing the calculus give us 20 residues.

b)  That’s it because every 7 Å there are 2 residues

c) First of all, is important to know that the residues of a protein define the secondary structure due to intermolecular and intramolecular interactions. Taking in account that the membrane bilayer has a lipid interior α-helical domains which are hydrophobic principally are embedded in membranes by hydrophobic interactions with the lipid interior of the bilayer favored by Van der Waals interactions and probably also by ionic interactions with the polar head groups of the phospholipids.