Cholesterol belongs to which major class of biomolecules in living organisms?

Introduction / Context:
Cholesterol is one of the most commonly discussed molecules in biology and health, especially in the context of heart disease, cell membranes, and hormones. To answer this question correctly, a learner needs to understand the basic classes of biomolecules and where cholesterol fits among them. This reinforces core concepts of biochemistry and human physiology that are very important for many competitive exams.

Given Data / Assumptions:

Cholesterol is a type of organic molecule found in animals, especially in cell membranes and blood.
Biomolecules are broadly grouped into four major classes: carbohydrates, lipids, proteins, and nucleic acids.
We assume standard biological classification as taught in school and undergraduate biology.

Concept / Approach:
To classify cholesterol, we recall the definitions of each biomolecule class. Carbohydrates are mainly sugars and polysaccharides used for energy and structure. Proteins are polymers of amino acids that perform structural and functional roles such as enzymes and transporters. Nucleic acids like DNA and RNA store and transmit genetic information. Lipids are a diverse group of hydrophobic or amphipathic molecules including fats, oils, phospholipids, and steroids. Cholesterol is a steroid, and steroids are a specific subgroup of lipids characterized by a four-ring carbon structure. Therefore, cholesterol clearly belongs to the lipid class.

Step-by-Step Solution:
Step 1: Recall that cholesterol has a multi-ring steroid structure and is not a sugar, protein, or nucleic acid. Step 2: Identify that steroids such as cholesterol, testosterone, and estrogen are classified as lipids. Step 3: Compare with carbohydrates, which are based on sugar units, and nucleic acids, which contain sugar, phosphate, and nitrogenous bases. Step 4: Conclude that cholesterol is correctly placed in the lipid group.

Verification / Alternative check:
Another way to confirm is to think about solubility. Lipids are generally insoluble in water and soluble in organic solvents. Cholesterol is hydrophobic and travels in the bloodstream bound to lipoproteins, which is typical behavior of lipids, not carbohydrates or proteins in their usual forms. This supports the classification of cholesterol as a lipid-derived molecule.

Why Other Options Are Wrong:
Carbohydrates: These are sugars and polysaccharides, not steroid ring molecules like cholesterol.
Nucleic acids: These are DNA and RNA, built from nucleotides, not steroid structures.
Proteins: These are polymers of amino acids and have completely different structures and functions compared to cholesterol.

Common Pitfalls:
A common mistake is to associate cholesterol directly with proteins because of terms like lipoproteins (HDL and LDL). However, lipoproteins are complexes of lipids and proteins, not cholesterol alone. Another error is assuming cholesterol is a carbohydrate simply because it is related to energy metabolism; this is incorrect because its structure and classification are clearly lipid-based.

Final Answer:
The correct classification is that cholesterol belongs to the class of lipids in biological systems.