How to read a peptide sequence

A peptide is written/read from the N-terminal end to the C-terminal end.

So we identify:

• the left end with free/amino-side as the first amino acid
• then the middle residue
• then the right end/carboxyl-side as the third amino acid

Identify each side chain from the given tripeptide structure

From the structure:

• First residue has side chain $-CH(CH_3)_2$. This corresponds to Valine (Val).

• Second residue has side chain $-CH_2OH$. This corresponds to Serine (Ser).

• Third residue has side chain $-CH(OH)CH_3$. This corresponds to Threonine (Thr).

Write the sequence from N-terminus to C-terminus

Therefore, the tripeptide sequence is: $\text{Val} - \text{Ser} - \text{Thr}$

Check options

• A: Val - Ser - Thr ✅
• B: Thr - Ser - Val ❌
• C: Leu - Ser - Thr ❌
• D: Thr - Ser - Leu ❌

Final answer

The correct option is A.