Which of the following is a wrong statement?

Hemoglobin is a fibrous protein

The correct answer is option 3. Hemoglobin is a fibrous protein.

Let us delve into each of the given statements:

1. Collagen is a fibrous protein:

Structure and Function: Collagen is one of the most abundant proteins in the human body, accounting for a significant portion of the extracellular matrix in tissues such as skin, bones, tendons, ligaments, and cartilage. It is characterized by its fibrous, elongated structure, composed of three polypeptide chains wound together in a triple helix formation. Each polypeptide chain is rich in glycine, proline, and hydroxyproline residues, which contribute to collagen's unique structure and stability.

Biomechanical Properties: Collagen provides structural support and tensile strength to tissues, helping to maintain their integrity and resilience against mechanical stress. In bone tissue, collagen fibers form the scaffold upon which calcium phosphate minerals are deposited, contributing to bone strength and density.

Skin Health: Collagen is essential for maintaining the structure and elasticity of the skin. It forms a network of fibers in the dermis, providing structural support and helping to prevent sagging and wrinkles. Collagen production declines with age, contributing to skin aging and the development of wrinkles.

2. Fibrous proteins are insoluble in water:

Solubility Properties: Fibrous proteins, including collagen, are characterized by their insolubility in water. This insolubility arises from their extended, repetitive structures, which lack significant hydrophilic (water-attracting) regions. Instead, fibrous proteins often contain hydrophobic (water-repelling) amino acid residues, which promote their aggregation into stable, insoluble structures, such as fibers or sheets.

Structural Role: The insolubility of fibrous proteins is crucial for their structural role in tissues. It allows them to form stable, insoluble structures that provide mechanical strength, support, and integrity to tissues exposed to mechanical stress. For example, collagen fibers in tendons and ligaments must withstand tension and stretching without dissolving in the surrounding aqueous environment.

3. Hemoglobin is a fibrous protein:

Structural and Functional Characteristics: This statement is incorrect. Hemoglobin is not a fibrous protein; it is a globular protein. Globular proteins are characterized by their compact, three-dimensional structures, which often have a spherical or globular shape. Hemoglobin consists of four polypeptide subunits—two alpha chains and two beta chains—each containing a heme group that binds oxygen. The globular structure of hemoglobin enables it to efficiently bind and transport oxygen in the bloodstream, as well as facilitate the release of oxygen to tissues.

Oxygen Transport: Hemoglobin's globular structure allows it to undergo conformational changes upon binding oxygen, transitioning between the tense (deoxygenated) and relaxed (oxygenated) states. This conformational flexibility is essential for its role in oxygen transport and delivery to tissues throughout the body.

4. Hemoglobin is a globular protein:

Structural and Functional Characteristics: This statement is correct. Hemoglobin is indeed a globular protein. As mentioned earlier, globular proteins have compact, three-dimensional structures, which are essential for their diverse functions. In the case of hemoglobin, its globular structure enables it to perform its function as an oxygen-carrying protein in red blood cells. The compact nature of globular proteins allows them to have diverse functions, such as enzymatic catalysis, transport of molecules, and regulation of cellular processes.

In summary, collagen is a fibrous protein known for its structural role and insolubility in water, while hemoglobin is a globular protein responsible for oxygen transport in the bloodstream. Understanding the distinction between fibrous and globular proteins is essential for comprehending their diverse functions and roles in biological systems.