Question

1) In an alpha helix, residue i is hydrogen bonded to

a) Residue i+3 through its side chain.

b) Residue i+3 through its backbone.

c) Residue i+4 through its side chain.

d) Residue i+4 through its backbone.

2) van der Waals force is a kind of electromagnetic force.

a) True

b) False

3) Which of the following interactions are generally considered to be unfavorable?

a) Interaction between Lys and Glu at neutral pH, assuming standard pKa values of Lys and Glu.

b) Interaction between a backbone amino group and a side chain carbonyl group.

c) Interaction between two alpha helices.

d) Interaction between Arg and Lys side chains at a pH of 7, assuming standard pKa values for Arg and Lys.

Answer 1

1. In an alpha-helix, the carboxyl group of one amino acid forms a hydrogen bond with amino group of another amino acid (4) residue down the chain and this is denoted as i + 4 – I hydrogen bonding . Thus the residue i is hydrogen bonded to residue i+4 through its backbone.

Therefore, the correct answer is option (d).

2. Van der Waals forces are a kind of intermolecular forces which are weak and short range forces that exist between uncharged molecules. Therefore, the statement is False.