Animated Solution for Chemistry - Organic Chemistry: The correct sequence of amino acids present in the tripeptide given below is

When you look at a complex biomolecule like a peptide, it might seem intimidating at first glance. However, just like reading a sentence, there is a systematic way to decode it. A tripeptide is simply a chain of three amino acids joined together by two peptide bonds. To figure out its name, we must identify the individual amino acid building blocks that make up the chain.

N-Terminus to C-Terminus

In biochemistry, there is a strict convention for reading and writing peptide sequences. We always read a peptide sequence from the N-terminus to the C-terminus.

The N-terminus is the end of the peptide chain with a free amino group ($-N{H}_2$), which is conventionally drawn on the left. The C-terminus is the end with a free carboxyl group ($-COOH$), drawn on the right. By following this left-to-right direction, we can systematically identify each amino acid residue.

To identify an amino acid within a peptide chain, we must look at its side chain, commonly referred to as the R group. The R group is attached to the alpha-carbon (the carbon atom immediately adjacent to the carbonyl carbon).

1. The First Amino Acid (N-terminus): Let's focus on the first amino acid on the far left. Its side chain is an isopropyl group, represented as $-CH(C{H}_3{)}_2$. The amino acid characterized by an isopropyl side chain is Valine (Val). Therefore, our sequence begins with Val.

2. The Second Amino Acid (Middle): Moving to the middle residue, we examine its side chain. It features a hydroxymethyl group, written as $-C{H}_{2}OH$. This specific side chain is the hallmark of Serine (Ser). Thus, the second amino acid in our sequence is Ser.

3. The Third Amino Acid (C-terminus): Finally, we look at the third amino acid located at the C-terminus. Its side chain consists of a carbon atom attached to both a methyl group and a hydroxyl group, forming a 1-hydroxyethyl group ($-CH(OH)C{H}_3$). This unique structure belongs to Threonine (Thr). So, our final amino acid is Thr.

Putting it all together from left to right, we have identified Valine, Serine, and Threonine. Therefore, the correct sequence of this tripeptide is Val-Ser-Thr.

It is crucial to understand that the sequence order is paramount. A peptide with the sequence Thr-Ser-Val would be a completely different molecule with distinct chemical and biological properties, even though it contains the exact same amino acids. The sequence defines the primary structure of a protein, which ultimately dictates its three-dimensional folding and biological function!