The number of possible dipeptides formed with two amino acids A and B are

Explanation

To determine the number of possible dipeptides that can be formed using two amino acids, A and B, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Number of Amino Acids (x)**:
- In this case, we have two amino acids: A and B. Therefore, \( x = 2 \).

2. **Determine the Length of the Peptide (y)**:
- A dipeptide consists of two amino acids linked together. Hence, the length of the peptide is \( y = 2 \).

3. **Use the General Formula**:
- The general formula for calculating the number of possible peptides of a given length from a set of amino acids is given by:
\[ \text{Number of peptides} = x^y \]
- Substituting the values we have:
\[ \text{Number of dipeptides} = 2^2 \]

4. **Calculate the Result**:
- Now, calculate \( 2^2 \):
\[ 2^2 = 4 \]

5. **List the Possible Dipeptides**:
- The possible dipeptides that can be formed with amino acids A and B are:
- AA
- AB
- BA
- BB

6. **Conclusion**:
- Therefore, the total number of possible dipeptides formed with amino acids A and B is 4.

### Final Answer:
The number of possible dipeptides formed with two amino acids A and B is **4**.