Question

Which of the following is the correct match? Acidic amino Basic amino Neutral amino acid acid (a) Glutamic acid Lysine \(\quad\) Valine \(\begin{array}{lll}\text { (b) lysine } & \text { Valine } & \text { Glutamic acid }\end{array}\) [c) Clutamic acid Valine Lysine (d) Lysine Glutamic acid Valine

Short answer

The correct match is (a) Glutamic acid (Acidic amino acid), Lysine (Basic amino acid), Valine (Neutral amino acid).

Step-by-step solution

- Understanding the Categories of Amino Acids

Amino acids are classified based on the pH level of their side chain groups. Acidic amino acids have a side chain that donates a proton, making them acidic. Basic amino acids have a side chain that accepts a proton, making them basic. Neutral amino acids have side chains that are neither strong proton donors nor acceptors.

- Identifying the Amino Acids

Glutamic acid is an acidic amino acid because it has a carboxylic acid group that can donate a proton. Lysine is a basic amino acid as it has an amino group in its side chain that can accept a proton. Valine is a neutral amino acid because it has an aliphatic hydrocarbon side chain that is neither acidic nor basic.

- Matching the Amino Acids to Their Properties

By comparing the properties of each amino acid to the categories provided, we can determine that glutamic acid matches the acidic category, lysine matches the basic category, and valine matches the neutral category.

Key concepts

Acidic Amino Acids

Acidic amino acids, such as glutamic acid, possess side chains that have the ability to donate a proton (H⁺), a characteristic that imparts these molecules with their acidic properties. This donation of a proton results in a negative charge at physiological pH levels.

Glutamic acid, for instance, features a side chain with a carboxylic acid group. This functional group, denoted as —COOH, can release a proton to become —COO^-, giving glutamic acid its acidic nature.

Significance in the Body

Acidic amino acids play critical roles in protein structure, by contributing to the formation of ionic bonds, and in metabolism, as they often appear at enzyme active sites.

Their ability to donate protons also means they can act as buffers, helping to maintain the pH balance within the body. An understanding of these properties is essential when it comes to predicting the behavior of proteins in various environments.

Basic Amino Acids

Basic amino acids, like lysine, feature side chains with groups that can readily accept a proton. At physiological pH, these amino acids carry a positive charge due to their amine groups, typically denoted as —NH₂, which can accept a proton to become —NH₃⁺.

The fundamental characteristic of basic amino acids is this ability to bind protons, making them essential for the structure and function of proteins.

Functions in Proteins

They form vital interactions in the tertiary and quaternary structures of proteins, holding components together through ionic bonds and often participating in the active sites of enzymes. Furthermore, basic amino acids contribute to the uptake and storage of positively charged molecules and ions within the cells, thus impacting cellular homeostasis and signaling.

Neutral Amino Acids

Neutral amino acids, such as valine, are characterized by side chains that neither donate nor accept protons significantly at physiological pH levels. These amino acids are not charged and primarily contribute to the hydrophobic core of protein structures.

Valine, in particular, has a side chain consisting of a branching aliphatic hydrocarbon which is neither acidic nor basic. This non-polarity allows valine and similar amino acids to stabilize protein structures by avoiding water and preferring to be buried within the protein interior.

Hydrophobic Interactions

Hydrophobic interactions facilitated by neutral amino acids are crucial for maintaining the proper folding and functionality of proteins. They are often found in the inner regions of proteins and play a significant role in defining the tertiary structure of the enzymes. Understanding the behavior of neutral amino acids helps in predicting protein folding patterns and stability.