Problem 85 - General Chemistry: Principles and Modern Applications

Question

The \(R\) group of valine is (a) \(-\mathrm{CH}_{2} \mathrm{OH}\) (b) \(-\mathrm{CH}_{2} \mathrm{COOH} ;(\mathrm{c})-\mathrm{CH}\left(\mathrm{CH}_{3}\right)_{2}\) (d) \(-\mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{NH}_{2}\); (e) none of these.

Step-by-Step Solution

Answer

The 'R' group of valine is (c) \(-\mathrm{CH}\left(\mathrm{CH}_{3}\right)_{2}\)

Step 1: Understanding the question

Firstly, it's important to understand that amino acids are composed of a basic structure: an amino group, a carboxyl group, a hydrogen atom, and an 'R' group or side chain, which is different for each amino acid and determines its properties. The question is asking for the 'R' group of valine, specifically.

Step 2: Recalling the structure of valine

The amino acid valine has an 'R' group that consists of a two-carbon aliphatic straight chain that branches off to a third carbon, which in turn is branched to two other carbon atoms, meaning its 'R' group is \(-\mathrm{CH}\left(\mathrm{CH}_{3}\right)_{2}\).

Step 3: Identifying the correct option

From the given options, it can be identified that (c) \(-\mathrm{CH}\left(\mathrm{CH}_{3}\right)_{2}\) is the correct 'R' group for valine.

Key Concepts

Valine Structure

Valine is one of the essential amino acids, meaning it's a vital component that our bodies cannot produce on their own and must be obtained from our diet. Structurally, valine belongs to the group of amino acids known as branched-chain amino acids (BCAAs). These are named for the branch-like arrangement of their carbon atoms. The overall structure of valine involves the standard backbone common to all amino acids, which includes:

• An amino group (\(-\text{NH}_2\))
• A carboxyl group (\(-\text{COOH}\))
• A hydrogen atom
• A unique 'R' group or side chain

This 'R' group makes valine distinctive among other amino acids and contributes to its role in the body, such as involvement in muscle growth and tissue repair. Understanding the unique structure of valine helps in grasping why it's crucial in dietary and physiological contexts.

R Group

In the world of amino acids, the 'R' group, also referred to as the side chain, is where all the chemistry happens. The 'R' group is what gives each amino acid its unique identity and properties. For valine, the 'R' group is particularly interesting because it consists of a branched chain that is hydrophobic. It looks like this: \[ -\text{CH}(\text{CH}_3)_2 \]This branched structure allows valine to be classified alongside leucine and isoleucine as a branched-chain amino acid (BCAA). Valine's hydrophobic nature means it likes to be near other similar non-polar molecules, which is why it is often found tucked into the interior of proteins, helping to stabilize their structures.
This 'R' group is critical in determining how valine interacts with other molecules. Its presence in proteins influences their 3-dimensional shapes and thus their functions.

Amino Acid Side Chain

The amino acid side chain sets each amino acid apart from the others, and its features dictate the role that particular amino acid plays in protein structure and function. Valine's side chain, as noted, is hydrophobic due to its branched aliphatic nature. Because of this, valine is frequently found away from the aqueous environment inside cells, nestled inside proteins where it can avoid contact with water.

• Hydrophobic side chains like valine's contribute to the formation of the protein's core, away from water.
• Interaction between these side chains helps to stabilize the folded form of proteins.

The side chain's characteristics are integral to the tertiary and quaternary structures of proteins. These structures dictate everything from the protein's solubility to its ability to bind to other molecules. In summary, valine isn't just a building block; its side chain's properties allow it to play specific roles in the biology of proteins, contributing to protein function and stability.