Chapter 21, Problem 8A

Interpretation Introduction

Interpretation: The number of unique amino acid sequences for a tripeptide with amino acid; gly, ala and cys with the condition of each amino acid occurring only once in each molecule needs to be determined.

Concept Introduction: Proteins are biomolecules, which are composed of certain monomer units such as amino acid. These are carboxylic acids with one amino group bonded on alpha-C atom of the molecule.

These amino acids are involved in condensation process to form peptides and polypeptides, which further form complex protein molecules. Amino acids are the organic molecules with both ${\text{–NH}}_{\text{2}}$ and $\text{–COOH}$ functional groups bonded on same C atom of the molecule.

Answer to Problem 8A

• Gly-Ala−Cys
• Gly-Cys-Ala
• Ala−Gly-Cys
• Ala-Cys-Gly
• Cys-Gly-Ala
• Cys-Ala-Gly

Explanation of Solution

The given amino acids can combine in different combinations of amino acids to give unique tripeptide. In a tripeptide, 3 amino acids combine through peptide linkage. There are total 6 possible combinations with 3 amino acids in such a way that no amino acid will repeat.

• Gly-Ala−Cys
• Gly-Cys-Ala
• Ala−Gly-Cys
• Ala-Cys-Gly
• Cys-Gly-Ala
• Cys-Ala-Gly

Conclusion

• Gly-Ala−Cys
• Gly-Cys-Ala
• Ala−Gly-Cys
• Ala-Cys-Gly
• Cys-Gly-Ala
• Cys-Ala-Gly