How many dipeptides are possible from two molecules of a typical `alpha`-amino acid ?

Explanation

To determine how many dipeptides can be formed from two molecules of a typical alpha-amino acid, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Dipeptides**: A dipeptide is formed when two amino acids are linked together by a peptide bond. This bond is formed through a condensation reaction where the carboxyl group of one amino acid reacts with the amino group of another, releasing a molecule of water.

2. **Identifying the Amino Acid**: Let's consider a typical alpha-amino acid, such as glycine (NH2-CH2-COOH). We will use two molecules of glycine for this example.

3. **Combining Two Molecules**: When we take two molecules of glycine, we can represent them as:
- Molecule 1: NH2-CH2-COOH
- Molecule 2: NH2-CH2-COOH

4. **Formation of the Peptide Bond**: The reaction involves the amino group (NH2) of one glycine molecule and the carboxyl group (COOH) of the other glycine molecule. The hydroxyl group (OH) from the carboxylic acid of one glycine and a hydrogen atom (H) from the amino group of the other glycine are removed to form water (H2O), resulting in the formation of a peptide bond.

5. **Resulting Dipeptide**: The resulting dipeptide from two glycine molecules is:
- Glycylglycine: NH2-CH2-CO-NH-CH2-COOH

6. **Counting Unique Dipeptides**: Since both molecules are identical (both are glycine), there is only one unique way to combine them to form a dipeptide. If the two amino acids were different, we could have different arrangements and thus more dipeptides. However, with two identical molecules, there is only one possible dipeptide.

### Final Answer:
Thus, the number of dipeptides that can be formed from two molecules of a typical alpha-amino acid is **1**.

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