Question

Starting with three different amino acids, how many different tripeptides can be made, assuming that each amino acid can be used more than once?

• A. 3
• B. 6
• C. 9
• D. 27

Hint:

Formula: $n^r$, where $n$ is types of amino acids and $r$ is the peptide length.

Answer 1

The Correct Option is D

Step 1: Concept
This is a problem of permutations with repetition.

Step 2: Meaning
A tripeptide has three positions to be filled. Since we can reuse amino acids, each position has the same number of choices.

Step 3: Analysis
For the first position, there are 3 choices. For the second, there are 3 choices. For the third, there are 3 choices. Total combinations = $3 \times 3 \times 3 = 3^3$.

Step 4: Conclusion
The total number of unique tripeptides possible is 27. Final Answer: (D)