Question

Identify the nonpolar amino acids and the acidic amino acids in the following peptide: Glu-Thr-Val-Asp-Ile-Ser-Ala

Short answer

Nonpolar: Val, Ile, Ala. Acidic: Glu, Asp.

Step-by-step solution

Identify Nonpolar Amino Acids

Nonpolar amino acids have side chains that are typically hydrophobic. These include Valine (Val), Isoleucine (Ile), and Alanine (Ala).

Identify Acidic Amino Acids

Acidic amino acids have side chains that carry a negative charge at physiological pH. These include Glutamic Acid (Glu) and Aspartic Acid (Asp).

List the Amino Acids

From the peptide sequence Glu-Thr-Val-Asp-Ile-Ser-Ala, identify and list: - Nonpolar amino acids: Val, Ile, Ala - Acidic amino acids: Glu, Asp

Key concepts

Nonpolar Amino Acids

Nonpolar amino acids have hydrophobic side chains, which means they do not interact well with water. Hydrophobic means 'water-fearing', so these amino acids prefer to stay away from water. These nature make them very important in the structure of proteins, helping them fold properly and maintain their shape. In the provided peptide sequence Glu-Thr-Val-Asp-Ile-Ser-Ala, the nonpolar amino acids are:

• Valine (Val)
• Isoleucine (Ile)
• Alanine (Ala)

These amino acids have side chains that are typically composed of hydrocarbons.
Because these side chains are nonpolar, they tend to be found in the interior of proteins, where they are shielded from water.

Acidic Amino Acids

Acidic amino acids have side chains that carry a negative charge at physiological pH, which is around 7.4. These amino acids play a crucial role in enzyme activity and in the binding of metal ions. The acidic amino acids in the peptide sequence Glu-Thr-Val-Asp-Ile-Ser-Ala are:

• Glutamic Acid (Glu)
• Aspartic Acid (Asp)

These side chains contain carboxyl groups, which lose a proton (H+) and become negatively charged when the pH rises above their pKa.
Because of their negative charge, acidic amino acids often interact with positively charged ions and amino acids.

Peptide Sequence Analysis

Analyzing peptide sequences involves identifying and categorizing the amino acids within a given peptide. Peptides are short chains of amino acids linked by peptide bonds. Here’s a simple approach to peptide sequence analysis:

• Step 1: List the amino acids in the peptide.
• Step 2: Group them based on their properties, such as nonpolar, polar, acidic, or basic.

In the peptide Glu-Thr-Val-Asp-Ile-Ser-Ala, we identified:

• Nonpolar amino acids: Val, Ile, Ala
• Acidic amino acids: Glu, Asp

This analysis helps in understanding the properties and potential functions of the peptide.

Side Chain Properties

The side chains of amino acids, also known as 'R groups', determine their properties and roles in proteins. Here are some important aspects:
1. Nonpolar Side Chains: Nonpolar side chains, like those found in Val, Ile, and Ala, are hydrophobic and contribute to the internal structure of proteins.
2. Acidic Side Chains: Acidic side chains, like those in Glu and Asp, are negatively charged and often involved in enzyme active sites and ionic interactions.
3. Polar Side Chains: These side chains can form hydrogen bonds, making them important in protein interactions with water and other molecules. Each type of side chain plays a role in the protein’s overall function and stability.
In peptides and proteins, the combination of different side chain properties leads to complex structures and functions.