On average, how many amino acids engaged in predominantly hydrophobic α-helices does it take to cross the hydrophobic part of the membrane?

The answer is 3.6 amino acids

Explanation:

The main chain of a polypeptide when folded in space adopts a conformation called helix ∝. In this structure each peptide bond establishes two hydrogen bonds. One of the hydrogen bonds is formed between the -NH- group of the amino acid peptide bond in position n and the -CO- group of the amino acid bond placed in position n-4. The second hydrogen bridge is formed between the group -CO- in position n and the group -NH- in position n + 4. Each turn of the helix is made up of 3.6 amino acids.

It will take up to 20-30 amino acids to cross the hydrophobic part of the membrane.

Explanation:

A helix is an element of protein structure that has two different side groups on both front and back .

In front ,it has a hydrophilic and at the back ,it has a hydrophobic group.

It will take averagely 20-30 amino acids to cross the hydrophobic part of the membrane.