Draw the structure of the tripeptide “Asp-Ala-Ile” at pH = 1. Then determine the total charge of the tripeptide.
The side chain of each amino acid is shown below in the form at pH = 7. (So when you use them to answer this question, you might need to modify the structures according to the given pH value.) Assume that all amino acids are in L-configuration.
To draw the structure of the tripeptide "Asp-Ala-Ile" at pH = 1, we need to consider the pKa values of the amino acids and their side chains.
1. Aspartic Acid (Asp): The side chain of Aspartic Acid has a pKa value of around 3.9. At pH = 1, the carboxyl group (-COOH) of Asp will be protonated and carry a positive charge, while the amino group (-NH2) will remain uncharged. Hence, the side chain will have a positive charge.
2. Alanine (Ala): Alanine is an aliphatic amino acid with a neutral side chain. At pH = 1, both the carboxyl group (-COOH) and the amino group (-NH2) will remain uncharged. There will be no net charge on the side chain.
3. Isoleucine (Ile): Isoleucine is also an aliphatic amino acid with a neutral side chain. Similar to Alanine, at pH = 1, both the carboxyl group (-COOH) and the amino group (-NH2) will remain uncharged. There will be no net charge on the side chain.
Now let's draw the structure of the tripeptide "Asp-Ala-Ile" with the appropriate charges at pH = 1:
NH3+ - CH - COOH
|
NH - CH - CH3
The charges on the side chains will be as follows:
Aspartic Acid (Asp) side chain: +1
Alanine (Ala) side chain: 0
Isoleucine (Ile) side chain: 0
To determine the total charge of the tripeptide, we need to consider the charges on the amino acid side chains. Since only the Aspartic Acid (Asp) side chain is positively charged, the total charge of the tripeptide at pH = 1 is +1.