Question

A turn in an α-helix is 5.40 Å long and consists of 3.60 AAs per turn. What is the length (in Å) of a 33000 Da single-stranded α-helical protein segment? Assume a mean residue mass of 110 Da. (1 Da = 1 g/mol).

Answer 1

Given the mass of single-stranded protein = 33000Da, and mean residue mass = 110 Da.

Therefore, number of amino acid residues can be calculated as 33000/110 = 300 residues.

Now each alpha-helix turn is 5.4 Angstrom long and consists of 3.6 AAs per turn. Therefore, length of one AA residue = 5.4/3.6 = 1.5 Angstrom.

Therefore, the length of a single stranded alpha-helical protein can be calculated as -

Length of protein = No. of AA residue in protein x Length of single AA residue = 300 x 1.5 A = 450 Angstroms