Question

You are taking a Biochemistry course and you find that you are interested in Proteins. To test if you have understood the basics, your advisor asks you to design a multi-faceted pentapeptide that matches ALL the following conditions at pH 7.0:

Positions 1 and 5 should have charged amino acid residues, but both cannot have the same charge. Positions 2 and 4 should have amino acid residues of opposite polarities but the residues cannot be charged and cannot be aromatic. Position 3 should be having an aromatic amino acid. Give the three letter name and 1 letter code for each amino acid.

Position 1: ______ Position 2: _______ Position 3: _______ Position 4: ______ Position 5: _______

Answer 1

Glu-Ser- Phe-Ala-Arg

ESFAR

Position 1: __Glu____ Position 2: __Ser_____ Position 3: __Phe_____ Position 4: __Ala____ Position 5: ___Arg____

At pH=7, both N-terminus, Glutamic acid and C-terminus Arginine will be protonated beacuse the pKa values are 9.5 and 9.0 respectively.

Serine is polar due to presence of CH2OH group. Alanine is non polar fits in to 2 and 4 position.

Phenyl glycine is an aromatic amino acid for position 3.

There could many other combination available, based on the given criteria. This is one of the possible sequence.