Problem 91 - A Complete Resource Book in Chemistry for JEE Main

Question

Which one of the following biomolecules is insoluble in water? (a) \(\alpha\)-keratin (b) haemoglobin (c) ribonuclease (d) adenine

Step-by-Step Solution

Answer

The insoluble biomolecule in water is \( \alpha \)-keratin.

Step 1: Define Solubility

Solubility is the ability of a substance (solute) to dissolve in a solvent. A substance that is insoluble cannot easily dissolve in the solvent, which in this case is water.

Step 2: Identify Properties of Each Biomolecule

Let's look at each biomolecule mentioned:- **(a) \(\alpha\)-keratin: This is a fibrous protein found in hair, nails, and the outer layer of skin. It is generally not soluble in water due to its structural role and the strong disulfide bonds that link its chains together.- **(b) haemoglobin: This is a globular protein that is soluble in water. It transports oxygen in the blood.- **(c) ribonuclease: This is an enzyme protein which is typically water-soluble and helps in cleaving RNA.- **(d) adenine: This is one of the four nucleobases in the nucleic acid of DNA and RNA. It is polar and can dissolve in water, though not as readily as some proteins.

Step 3: Determine the Most Insoluble Biomolecule

Considering the properties of each: - **\(\alpha\)-keratin: Not soluble in water due to its tough structural nature and linkage.- **haemoglobin and ribonuclease** are known to be soluble due to their globular and enzymatic nature, respectively.- **adenine**, even though it's slightly soluble, is not as insoluble as \(\alpha\)-keratin.Therefore, the most insoluble biomolecule in water among the options given is **(a) \(\alpha\)-keratin.

Key Concepts

Understanding Alpha-Keratin

Alpha-keratin is a type of protein found in mammalian hair, nails, and the outer layer of skin. This protein is fibrous in nature, distinguishing it from other soluble proteins. The primary role of alpha-keratin is structural, providing strength and protection.

Alpha-keratin is composed of polypeptide chains that are arranged in a coiled pattern. These coils are stabilized by strong disulfide bonds, which link sulfur atoms from different chains together. This strong linkage is vital in maintaining the rigidity and insolubility of alpha-keratin in water.

• Found in hair and nails
• Stabilized by disulfide bonds
• Insoluble in water

Alpha-keratin does not easily dissolve in water due to its structural role and robust bonding, making it essential for protective tissues in mammals.

The Role of Haemoglobin

Haemoglobin is a globular protein, which is very different from fibrous proteins like alpha-keratin. It is primarily responsible for transporting oxygen from the lungs to the tissues and returning carbon dioxide from the tissues to the lungs.

Its solubility in water is crucial because it must exist within the aqueous environment of the blood plasma. The structure of haemoglobin consists of four subunits, each containing an iron molecule that binds to oxygen. This capability to transport gases makes haemoglobin vital for respiratory processes.

• Globular structure
• Soluble in water
• Transports oxygen in blood

The globular shape and specific amino acid sequence of haemoglobin allow it to dissolve and function efficiently in the watery environment of our body's blood.

Functions of Ribonuclease

Ribonuclease is an enzyme protein designed to catalyze the breakdown of RNA into smaller components. This enzyme activity is essential in various biological processes including the degradation of RNA in cells.

Enzymes like ribonuclease are typically water-soluble due to their roles in processing biochemical reactions that occur in aqueous environments. The solubility ensures that ribonuclease can freely interact with RNA strands during the catalytic process.

• Water-soluble enzyme
• Catalyzes RNA breakdown
• Essential for RNA processing

Ribonuclease's solubility in water is crucial for its function in biological systems, facilitating the manipulation of RNA molecules within a cell.

Properties of Adenine

Adenine is one of the four nucleobases used in the formation of nucleic acids like DNA and RNA. These nucleobases are the building blocks of genetic material, playing a crucial role in coding, decoding, and expressing genes.

Adenine is a polar molecule, allowing it a moderate degree of solubility in water. However, compared to other proteins and enzymes, its solubility is not very high. Despite this limited solubility, adenine plays vital roles in various biochemical processes, including energy transfer in cells through molecules like ATP.

• Polar nucleobase
• Moderate water solubility
• Component of DNA and RNA

Adenine's solubility is sufficient to participate in necessary biochemical pathways while contributing to the structural integrity of genetic material.