Calculate the length of an alpha helix that is 120 amino aci

Calculate the length of an alpha helix that is 120 amino acids long. What will be the length of the same chain if it is not in an alpha helix (distance between 2 Amino acids is 0.35 nm)

Solution

In alfa helix each turn contain 3.6 Amino acids and each helix length is 5.4 Angstom units. So each amino acid length in alfa helix is 5.4 / 3.6 = 1.5 Angstrom Units. If alfa helix contain 120 Amino acids, then length of the helis 1.5 x 120 = 180 Angstrom units or 18 nm

In case of linear structure I.e Beta sheets each amino acid length is 0.35 nm or 3.5 Angstrom units. So tatal length is 3.5 x 120 = 420 Angstrom Units or 42 nm