How many different tripeptides can be obtained from alanine, glycine and phenylalanine, each tripeptide containing all the three amino acids?

Options

A. 8
B. 6
C. 7
D. 5

Explanation

To determine how many different tripeptides can be formed from the amino acids alanine (A), glycine (G), and phenylalanine (F), we need to consider the arrangement of these three amino acids in sequences of three.

### Step-by-Step Solution:

1. **Identify the Amino Acids**: We have three amino acids: Alanine (A), Glycine (G), and Phenylalanine (F).

2. **Understanding Tripeptides**: A tripeptide consists of three amino acids. Since we want each tripeptide to contain all three amino acids, we will be arranging A, G, and F in different sequences.

3. **Calculating Permutations**: The number of different arrangements (permutations) of n distinct items is given by the formula n!. Here, n = 3 (for A, G, and F).

\[ \text{Number of tripeptides} = 3! = 3 \times 2 \times 1 = 6 \]

4. **Listing the Tripeptides**: The different arrangements of A, G, and F are:
- AGF
- AFG
- GAF
- GFA
- FAG
- FGA

5. **Conclusion**: Therefore, the total number of different tripeptides that can be formed from alanine, glycine, and phenylalanine, each containing all three amino acids, is 6.

### Final Answer:
The number of different tripeptides that can be obtained is **6**.

---