(i) Met, Ser, Leu ------------------------------------------------------------- (ii) Ile, Ser, Phe ------------------ I have calculated the above polypeptides, can anyone explain why changing (i) to (ii) may change the function of the new protein?

To understand why changing the sequence of amino acids in a polypeptide chain may change the function of a protein, we need to consider the role of amino acids in protein structure and function.

Proteins are composed of long chains of amino acids that fold into specific three-dimensional structures. The sequence of amino acids in a polypeptide chain determines how it will fold and therefore its overall structure. The specific structure of a protein is crucial for its function.

Each amino acid has a unique side chain, which determines its chemical properties. These side chains can interact with other amino acids in the chain or molecules in the surrounding environment. These interactions play a vital role in protein function.

Now, let's apply this knowledge to the given example:
(i) Met, Ser, Leu
(ii) Ile, Ser, Phe

In the original sequence (i), we have the amino acids Methionine (Met), Serine (Ser), and Leucine (Leu). Changing the sequence to (ii) replaces Methionine with Isoleucine (Ile), while keeping Serine and replacing Leucine with Phenylalanine (Phe).

Since proteins fold into distinct three-dimensional structures based on their amino acid sequence, even a slight change in the sequence can impact this folding. Altering one or more amino acids may disrupt critical interactions within the protein, affecting its overall structure and potentially its function.

The specific functions of proteins are often determined by the presence of functional domains. These domains consist of specific sequences of amino acids that contribute to a particular function, such as binding to other molecules or catalyzing chemical reactions. Changing the amino acids within these functional domains can disrupt their structure and consequently affect the protein's ability to perform its specific function.

In summary, changing the amino acid sequence in a polypeptide chain can alter the protein's folding pattern, disrupt critical interactions, and potentially affect the structural integrity and function of the protein.