Question

Draw the structures of the tripeptides gly-ala-ser and ser-alagly. How many other tripeptides are possible using these three amino acids?

Short answer

The tripeptide structures of Gly-Ala-Ser and Ser-Ala-Gly are as follows: Gly-Ala-Ser: NH2-CH2-C(=O) | NH-CH(CH3)-C(=O) | NH-CH(CH2OH)-COOH Ser-Ala-Gly: NH2-CH(CH2OH)-C(=O) | NH-CH(CH3)-C(=O) | NH-CH2-COOH There are 6 possible tripeptides using these three amino acids, and since we have already illustrated two, there are 4 other possible tripeptides.

Step-by-step solution

Understanding the amino acid structures

To draw the structures of the tripeptides, we first need to know the structures of each amino acid. Here are the structures of Gly, Ala, and Ser: Glycine (Gly): - Amino group: NH2 - Carboxyl group: COOH - Side chain (R group): H Alanine (Ala): - Amino group: NH2 - Carboxyl group: COOH - Side chain (R group): CH3 Serine (Ser): - Amino group: NH2 - Carboxyl group: COOH - Side chain (R group): CH2OH

Drawing the structure of Gly-Ala-Ser

To draw the tripeptide structure Gly-Ala-Ser, we will connect the amino acids in the following sequence: Glycine - Alanine - Serine. The peptide bond (amide bond) is formed by connecting the amino group of the next amino acid with the carboxyl group of the previous amino acid, with the elimination of water. Structure of Gly-Ala-Ser: NH2-CH2-C(=O) | NH-CH(CH3)-C(=O) | NH-CH(CH2OH)-COOH

Drawing the structure of Ser-Ala-Gly

Similarly, to draw the tripeptide structure Ser-Ala-Gly, we will connect the amino acids in the following sequence: Serine - Alanine - Glycine. Structure of Ser-Ala-Gly: NH2-CH(CH2OH)-C(=O) | NH-CH(CH3)-C(=O) | NH-CH2-COOH

Calculating the number of other possible tripeptides

Since we have three amino acids (Gly, Ala, and Ser), and we can use each amino acid once in a tripeptide, there are 3! (3 factorial) possible tripeptides (the ordering matters). 3! = 3 × 2 × 1 = 6 possible tripeptides We already have two of the tripeptides (Gly-Ala-Ser and Ser-Ala-Gly). Therefore, the number of other possible tripeptides using these three amino acids is: 6 (total possible tripeptides) - 2 (given tripeptides) = 4 other tripeptides