Question

For the following amino acid strand (shown from N to C-terminus)

Asp-Pro-Cys-Gly-Ser-Try

A.) Draw the structure of the hexapeptide w/ appropriate stereochemistry.   

B.) What forces hold the above peptide in an α-helix? What part of the peptide is involved?

C.) This hexapeptide is one of three peptide chains in a protein. What forces hold the above peptide in its 4o structure?

Answer 1

A) This is the drawing of the chain without forming any secondary structure:

Note that the Pro in the second residue distorts the configuration

B) The alpha helices are formed by Hydrogen bonds, the hydrogen from the amino group of an amino acid bonds to the oxygen from the carboxylic group in another amino acid located 4 residues away.

C) For that we have to pay attention to the specific amino acids forming the sequence, pay attention to their R groups. For example Cys is the one able to form disulfide bonds, Pro haS a big hydrophobic group, while Ser, Tyr and Asp have hydrophilic groups.

The forces that hold together the quaternary structure are disulphide bonds.