Question

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

Short answer

(a) \( \alpha \)-keratin is insoluble in water.

Step-by-step solution

Understanding Solubility in Water

To determine which biomolecule is insoluble, we must recognize that solubility often depends on the chemical nature of the biomolecule. In general, biomolecules that are non-polar or have large non-polar regions tend to be insoluble in water, which is a polar solvent.

Evaluating Each Option

Let's examine each biomolecule: - (a) \( \alpha \)-keratin: A fibrous protein predominantly found in hair and nails, known for having hydrophobic (water-repelling) properties due to its non-polar amino acid composition.- (b) haemoglobin: A globular protein that is soluble in water; it transports oxygen in the blood.- (c) ribonuclease: An enzyme protein that is water-soluble because it catalyzes reactions within aqueous environments.- (d) adenine: A nitrogenous base, part of nucleic acids, which can interact with water through hydrogen bonding.

Identifying the Answer

Given that \( \alpha \)-keratin is predominantly non-polar and is a structural protein with insoluble characteristics in aqueous solutions, it is the correct choice among the options. Haemoglobin, ribonuclease, and adenine have interactions that allow them to dissolve or be suspended in water.

Key concepts

Non-polar Proteins

Non-polar proteins are fascinating because they exhibit unique behaviors in aqueous environments like water. These proteins are generally made up of amino acids that have non-polar side chains. Since water is a polar solvent, non-polar proteins tend to repel water and prefer to be in environments that do not have a lot of water.

The primary reason is simple: non-polar means that the proteins lack charged groups. They don't generally mix well with water, much like oil and water. This property also influences how these proteins are structured and where they are found in nature. For example, many non-polar proteins are structural proteins, meaning they are solid and not easily soluble in water. Examples include proteins like \(\alpha\)-keratin, which is the protein that makes up hair and nails.

• Hydrophobic Interactions: This term describes how non-polar proteins can be water-repellent and therefore make them insoluble in water.
• Applications: Non-polar proteins are often found where durability and stability are needed, such as in constructional areas of our bodies.

Understanding why some proteins are non-polar and their roles can help you better grasp the concepts of solubility and protein functionality.

Water-soluble Biomolecules

Unlike their non-polar counterparts, water-soluble biomolecules are exactly what their name suggests—they dissolve well in water. This makes them adept at performing functions that occur within aqueous environments, like the human body. These biomolecules contain polar or charged regions that can readily interact with water molecules.

These interactions often occur through hydrogen bonding or ionic interactions, where the biomolecules form attractive forces with the water's polar molecules. Examples include proteins like haemoglobin, which carries oxygen in the blood, and ribonuclease, an enzyme that catalyzes reactions in the presence of water.

• Hydrophilic Properties: These properties allow water-soluble biomolecules to easily mix with water.
• Functional Significance: Water-solubility is crucial for biomolecules such as enzymes and transport proteins which must function in bodily fluids.

Understanding the different ways biomolecules interact with water is essential for analyzing their biological roles.

Protein Structure and Function

The structure and function of proteins are fascinating subjects that illustrate how these biomolecules work in living organisms. Proteins are composed of long chains of amino acids folded into intricate shapes, which dictate their function. Each protein's shape is significant because it determines its specific role in the body.

The structure of a protein can be divided into four levels: primary, secondary, tertiary, and quaternary. Each level of structure builds upon the one before it, creating a complex and functional protein.

• Primary Structure: This is the sequence of amino acids in the protein. The order in which these amino acids are linked determines the protein's ultimate shape and function.
• Secondary Structure: Involves the local folding of the polypeptide chain into structures like alpha-helices and beta-sheets.
• Tertiary Structure: Refers to the overall three-dimensional shape of a protein.
• Quaternary Structure: Some proteins are made of multiple polypeptide chains, resulting in a quaternary structure.

The function of a protein often correlates directly with its structure. For instance, the shape of the protein haemoglobin is perfectly suited for oxygen transport in the blood. Understanding protein structures will give you insights into their diverse biological roles.