Chapter 21, Problem 10A

Interpretation Introduction

Interpretation:The structures of six different tripeptide possible from phenylalanine, alanine and glycine (each taken only once) needs to be drawn. The peptide bonds needs to be circled. The terminal amino and carboxyl groups need to be labelled.

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 10A

• Phenylalanine-alanine -glycine
• Phenylalanine-glycine-alanine
• Alanine-glycine-phenylalanine
• Alanine-phenylalanine-glycine
• Glycine-alanine-phenylalanine
• Glycine-phenylalanine-alanine

Explanation of Solution

In a tripeptide, N-terminus must be written on left side whereas the C-terminus must be on right side. There are 6 possible combinations with phenylalanine, alanine and glycine are:

• Phenylalanine-alanine -glycine
• Phenylalanine-glycine-alanine
• Alanine-glycine-phenylalanine
• Alanine-phenylalanine-glycine
• Glycine-alanine-phenylalanine
• Glycine-phenylalanine-alanine

The structure of tripeptide phenylalanine-alanine -glycine is as follows:

  

Here, peptide bonds, terminal amino and carboxylic groups are labelled as follows:

  

The structure of tripeptide phenylalanine-alanine -glycine is as follows:

  

Phenylalanine-glycine-alanine

Here, peptide bonds, terminal amino and carboxylic groups are labelled as follows:

  

The structure of tripeptide Alanine-glycine-phenylalanine is as follows:

  

Here, peptide bonds, terminal amino and terminal carboxylic group are represented as follows:

  

The structure of alanine-phenylalanine-glycine is as follows:

  

Here, peptide bonds, terminal amino and terminal carboxylic group are represented as follows:

  

The structure of Glycine- alanine- phenylalanine is as follows:

  

Here, peptide bonds, terminal amino and terminal carboxylic group are represented as follows:

  

The structure of Glycine-phenylalanine-alanine is as follows:

  

Here, peptide bonds, terminal amino and terminal carboxylic group are represented as follows:

  

Conclusion

Thus, three amino acids can form 6 possible combinations.