Problem 9 - Objective Biology for NEET

Question

Lipids are extracted with acid insoluble fraction because (a) Its molecular weight is less than \(800 \mathrm{Da}\) (b) It form vesicle or micelle which are not water soluble (c) It is a polymer (d) It is not a polymer

Step-by-Step Solution

Answer

The correct answer is (b): Lipids are extracted with acid insoluble fraction because they form vesicles or micelles, which are not water soluble.

Step 1: Understanding lipid characteristics

Lipids are a type of organic compounds, which are water insoluble, and form vesicles or micelles. They are not a polymer and their molecular weight varies widely depending on the types of lipid molecules, but they are typically above 800 Da.

Step 2: Evaluating each option

Option (a) is not correct because lipids often have a molecular weight above 800 Da. Option (c) and (d) can be eliminated, as lipids are not a type of polymer. The only remaining option is (b) which states that lipids form vesicles or micelles which are not water soluble, an accurate property of lipids.

Step 3: Confirming the final answer

The final answer is option (b). Lipids are extracted with acid insoluble fraction because they form vesicles or micelles, which aren't soluable in water.

Key Concepts

Micelles

Lipids, when present in an aqueous environment, can organize into unique structures known as micelles. This is because lipids have both hydrophobic and hydrophilic parts. The tail, or the hydrophobic part, repels water while the head, or hydrophilic part, interacts with it.
As a result of these opposing forces, micelles form spontaneously by arranging the hydrophobic tails inward, away from the water, and the hydrophilic heads outward toward the water.
This organization creates a spherical structure that traps the hydrophobic substances inside.

• Micelles form naturally when amphiphilic molecules like fatty acids are present in water.
• They are crucial for processes like digestion, where they help in the absorption of fat-soluble vitamins and lipids.

Micelles are usually formed when lipid concentrations exceed a certain critical level called the critical micelle concentration (CMC). At this point, the energy cost of forming a micelle is outweighed by the energetically favorable interactions when water molecules bind to the hydrophilic head.

Vesicles

Vesicles are somewhat larger than micelles and play a pivotal role in biological systems. Unlike micelles, which are single-layered, vesicles are typically composed of a bilayer of lipids.
This bilayer forms a small spherical sac, resembling a small compartment that can encapsulate substances, including drugs, nutrients, or even waste products.
The bilayer properties make vesicles important for several biological functions:

• They act as transport vehicles, moving substances within or between cells.
• They can facilitate communication between cells by merging with cell membranes.
• They provide a controlled environment for various biochemical reactions and processes.

Vesicles can form naturally in cells although they can also be artificially created. Liposomes, a type of synthetic vesicle, are used in drug delivery, demonstrating how vesicles can be leveraged in medical applications.

Water Insoluble Substances

Lipids are classified as water-insoluble substances due to their long hydrophobic tails. This insolubility arises from the fact that lipids do not mix well with water and tend to aggregate, forming structures such as micelles and vesicles.
The properties that contribute to the water insolubility of lipids are:

• The presence of long hydrocarbon chains that repel water.
• A lack of extra charge or polar groups that could interact with water molecules to create soluble forms.

Insoluble substances like lipids are crucial as they make up cell membranes, providing structure while maintaining a necessary barrier in aqueous environments.
Their insolubility also allows them to store energy efficiently because they do not dissolve or disperse in body fluids, ensuring storage until needed. This property of lipids is vital for energy management and cell integrity.