Use your knowledge of amino acid characteristics to order the peptides below acc

Question

Use your knowledge of amino acid characteristics to order the peptides below according to the net charge contributed by their side chains at physiological pH (~pH 7). Use the single-letter amino acid designations to generate your list, placing the most negatively charged peptide on the left and the most positively charged peptide on the right. In addition, for each peptide, list the total number of positive and negative charges. Remember that, at neutral pH, the amino terminus carries a positive charge and the carboxyl terminus carries a negative charge.

A. YGAKKRAS

B. ARRKSTRK

C. DERKQNST

D. DDAEIYSA

E. NQSTYEEG

Explanation / Answer

At pH= 7, there are two negatively charged amino acids- Aspartic acid and glutamic acid . Each of them having a net charge of (-1).

And two positively charged amino acids- Lysine and Arginine .Each having a net charge of (+1).

Now calculating the net charge of each peptide chain-

A) YGAKKRAS- Tyr-Gly-Ala-Lys-Lys-Arg-Ala-Ser. 0+0+0+1+1+1+0+0=+3

B)ARRKSTRK- Ala-Arg-Arg-Lys-Ser-Thr-Arg-Lys. 0+1+1+1+0+0+1+1=+5

C)DERKQNST- Asp-Glu-Arg-Lys-Gln-Asn-Ser-Thr. -1-1+1+1+0+0+0= 0

D)DDAEIYSA- Asp-Asp-Ala-Glu-Ile-Tyr-Ser-Ala. -1-1+0-1+0+0+0+0=-3

E)NQSTYEEG-Asn-Gln-Ser-Thr-Tyr-Glu-Glu-Gly. 0+0+0+0+0-1-1+0= -2

Arrangement of peptide chain starting from most negatively charged to positively charged- D-E-C-A-B

DDAEIYSA-NQSTYEEG-DERKQNST-YGAKKRAS-ARRKSTRK.

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