Problem 38 - A Complete Resource Book in Chemistry for JEE Main

Question

Fibrous protein are insoluble in (a) water (b) strong base (c) strong acid (d) both (b) and (c)

Step-by-Step Solution

Answer

Fibrous proteins are insoluble in both strong acids and bases (option d).

Step 1: Understanding Fibrous Proteins

Fibrous proteins are structural proteins that typically have elongated fiber-like shapes. They are not involved in biochemical reactions but are rather important for structural support, providing strength and elasticity. Examples include collagen, keratin, and elastin.

Step 2: Insolubility Characteristic of Fibrous Proteins

Fibrous proteins generally have low solubility in water because their structure is heavy and stable, due to extensive hydrogen bonding and hydrophobic interactions within the chains. This nature means they maintain their shape and form in various environments, instead of dissolving.

Step 3: Solubility in Acidic and Basic Environments

While fibrous proteins are generally insoluble in water, they can also be resistant to dissociation in strong acids and bases. This is due to their stable polypeptide chains and the nature of the interactions holding these chains together, which are not easily disrupted by pH changes.

Step 4: Analyzing the Options

We are required to determine in which medium fibrous proteins are insoluble. From the previous steps, fibrous proteins are not readily soluble in water, nor are they easily disrupted by strong acids and bases due to their stable structure. Therefore, the correct choice would encompass both conditions mentioned in the options.

Key Concepts

Protein Structure

Proteins have a wide range of structures, which determine their function and role in various biological processes. The primary structure of a protein is its sequence of amino acids linked together by peptide bonds, forming a chain. This sequence dictates how the protein will fold into its three-dimensional structure. In particular, fibrous proteins display a unique elongated shape which attributes to their role as structural components in the body, such as providing support and strength to tissues.
This fibrous nature is characterized by long strands or sheets, with minimal folding compared to other protein types. These strands make fibrous proteins perfect for their structural roles as they are strong and durable, which is essential for materials intended to support or protect, such as in hair (keratin) or connective tissues (collagen).

• The primary structure: Sequence of amino acids.
• The secondary structure: Localized folding into alpha-helices or beta-sheets.
• The tertiary structure: Overall 3D shape, stabilizing the interaction between chains.
• The quaternary structure: Multi-subunit assemblies.

Hydrophobic Interactions

Hydrophobic interactions play a critical role in the stability and function of fibrous proteins. These non-covalent interactions occur when nonpolar side chains minimize exposure to water by clustering together within the protein structure. This behavior is crucial in fibrous proteins because it enhances their structural integrity.
In an aqueous environment, these hydrophobic interactions help proteins maintain their shape by avoiding water. In fibrous proteins, such interactions contribute to their insolubility in water. The hydrophobic sections of their polypeptide chains prefer to stay buried inside the structure, away from contact with water, reinforcing the protein's stability and resistance to solubility.

• Nonpolar side chains: Avoid water and cluster together.
• Stability: Enhanced by minimizing the surface area exposed to aqueous environments.
• Insolubility in water: Supported by hydrophobic clustering.

Polypeptide Chains

Polypeptide chains are the building blocks of proteins, composed of amino acids linked by peptide bonds. In fibrous proteins, these chains are arranged in long strands or sheets. This linear arrangement is crucial for the structural roles these proteins fulfill.
The rigidity and strength of fibrous proteins are largely due to the way these polypeptide chains interact with each other. They form extensive hydrogen bonds and other interactions, making the overall structure quite stable and resistant to changes in environmental conditions.
This resistance is essential as fibrous proteins need to maintain their structural integrity, even in varying pH levels or in the presence of stronger solvents. The arrangement and interactions between these chains help them achieve it.

• Composed of amino acids linked by peptide bonds.
• Strength and rigidity: Achieved through hydrogen bonding and interactions.
• Stability: Crucial for maintaining structural integrity.

Protein Solubility

The solubility of proteins is determined by their structural properties and the environment they are placed in. Fibrous proteins, known for their elongated shapes and extensive cross-linking, are typically insoluble in water and maintain this property across various conditions, including exposure to strong acids and bases.
The insolubility of fibrous proteins is primarily due to hydrophobic interactions and strong intra-chain bonding. These factors make it difficult for the protein to break down or dissolve, even when subjected to environmental changes. For instance, fibrous proteins like collagen maintain their shape and function in tissues that are exposed to different chemical environments.
This characteristic is beneficial in biological contexts where proteins need to remain intact and functional over time, irrespective of soluble interactions.

• Factors affecting solubility: Structure and bonding.
• Environmental influence: Strong acids and bases have minimal impact.
• Functional over time: Maintains structure despite environmental changes.