Question

A tetrapeptide is made of naturally occurring alanine, serine, glycine, and valine. If the C-terminal amino acid is alanine and the N-terminal amino acid is chiral, the number of possible sequences of the tetrapeptide is: 
 

• A. 4
• B. 8
• C. 6
• D. 12

Hint:

Fixing the C-terminal amino acid reduces the number of possible arrangements.

Answer 1

The Correct Option is A

Step 1: Understanding Peptide Sequence Formation 
- A tetrapeptide consists of 4 amino acids. 
- The C-terminal amino acid is fixed as alanine. 
- The N-terminal must be chiral (valine or serine). 
Step 2: Listing Possible Sequences 
Since glycine is achiral, the N-terminal choices are valine or serine, leading to 4 possible arrangements:
1. Val-Gly-Ser-Ala 
2. Val-Ser-Gly-Ala 
3. Ser-Gly-Val-Ala 
4. Ser-Val-Gly-Ala 
Final Answer: The correct number of sequences is 4.