Cysteine and methionine are both sulfur-containing amino acids. However, the side chain of cysteine is polar, while the side chain of methionine is nonpolar. Write the structures of the two dipeptides produced using these two amino acids and indicate the peptide bond in each.

Oxytocin is a neuropeptide hormone that has nine amino acids. Determine the number of peptide bonds present in oxytocin.

i. Show the line-angle structure for isoleucylthreonylserinylphenylalanine.

ii. Provide its three-letter abbreviation

iii. Provide its one-letter abbreviation.

(Ignore stereochemistry)

Draw the structure for the peptide Lys–Phe–Asp and write the one-letter abbreviation. (Ignore stereochemistry)

Provide the products of the condensation reaction shown below. (Assume that they bond in the order shown.)

For the following tripeptide, identify and label the N-terminal amino acid and C-terminal amino acid. Provide the name for each.

Give the skeletal structure for the peptide IYQ. (Ignore stereochemistry)