Biomolecules – Complete Notes for NEET

 

Introduction

Biomolecules are the chemical compounds present in living organisms. They form the structural and functional basis of life. Understanding biomolecules is crucial for NEET as questions are frequently asked from carbohydrates, proteins, lipids, enzymes, and nucleic acids.

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What are Biomolecules?

Biomolecules are organic and inorganic substances found in living organisms that participate in various biological functions.

Examples:

• Carbohydrates

• Proteins

• Lipids

• Nucleic Acids

• Water

• Minerals

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Types of Biomolecules

Biomolecules can be classified into:

1. Inorganic Biomolecules

• Water

• Mineral ions

2. Organic Biomolecules

• Carbohydrates

• Proteins

• Lipids

• Nucleic Acids

• Vitamins

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Carbohydrates

Carbohydrates are organic compounds made of carbon, hydrogen, and oxygen.

General Formula:

(CₙH₂ₙOₙ)

Functions:

• Primary source of energy

• Energy storage

• Structural components

Classification

A. Monosaccharides

Simplest sugars that cannot be hydrolyzed further.

Examples:

• Glucose

• Fructose

• Ribose

B. Disaccharides

Formed by two monosaccharides.

Examples:

• Sucrose = Glucose + Fructose

• Maltose = Glucose + Glucose

• Lactose = Glucose + Galactose

C. Polysaccharides

Long chains of monosaccharides.

Examples:

• Starch (Plant storage)

• Glycogen (Animal storage)

• Cellulose (Plant cell wall)

• Chitin (Exoskeleton of arthropods)

Important NEET Facts

• Cellulose is the most abundant organic compound on Earth.

• Glycogen is called animal starch.

• Ribose is present in RNA.

• Deoxyribose is present in DNA.

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Proteins

Proteins are polymers of amino acids linked by peptide bonds.

Functions

• Structural support

• Enzyme formation

• Hormone synthesis

• Transport

• Defense

Amino Acid Structure

Each amino acid contains:

• Amino group (-NH₂)

• Carboxyl group (-COOH)

• Hydrogen atom

• Variable R-group

Peptide Bond

A peptide bond is formed between the amino group of one amino acid and the carboxyl group of another amino acid.

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Levels of Protein Structure

1. Primary Structure

Linear sequence of amino acids.

2. Secondary Structure

• α-Helix

• β-Pleated Sheet

3. Tertiary Structure

Three-dimensional folding.

4. Quaternary Structure

Association of multiple polypeptide chains.

Example:

• Hemoglobin

Important NEET Facts

• Collagen is the most abundant protein in animals.

• Insulin was the first protein to be sequenced.

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Lipids

Lipids are water-insoluble organic molecules composed mainly of carbon, hydrogen, and oxygen.

Functions

• Energy storage

• Cell membrane formation

• Hormone synthesis

• Insulation

Types of Lipids

Simple Lipids

• Fats

• Oils

Compound Lipids

• Phospholipids

• Glycolipids

Derived Lipids

• Steroids

• Cholesterol

Important NEET Facts

• Phospholipids form the cell membrane.

• Lipids provide about twice as much energy as carbohydrates.

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Nucleic Acids

Nucleic acids are polymers of nucleotides responsible for storage and transmission of genetic information.

Types

DNA (Deoxyribonucleic Acid)

Functions:

• Stores genetic information

• Controls heredity

Components:

• Deoxyribose sugar

• Phosphate group

• Nitrogenous base

Bases:

• Adenine (A)

• Guanine (G)

• Cytosine (C)

• Thymine (T)

RNA (Ribonucleic Acid)

Functions:

• Protein synthesis

Components:

• Ribose sugar

• Phosphate group

• Nitrogenous bases

Bases:

• Adenine (A)

• Guanine (G)

• Cytosine (C)

• Uracil (U)

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Nitrogenous Bases

Purines

Double-ring structure:

• Adenine

• Guanine

Pyrimidines

Single-ring structure:

• Cytosine

• Thymine

• Uracil

Base Pairing Rules

• A = T (2 Hydrogen Bonds)

• G ≡ C (3 Hydrogen Bonds)

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Nucleotide vs Nucleoside

Nucleoside

Sugar + Nitrogenous Base

Nucleotide

Sugar + Base + Phosphate

Example

• Adenosine = Nucleoside

• AMP (Adenosine Monophosphate) = Nucleotide

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Enzymes

Enzymes are biological catalysts that speed up biochemical reactions.

Characteristics

• Mostly proteins

• Highly specific

• Remain unchanged after reaction

• Lower activation energy

Components

Apoenzyme

Protein part

Cofactor

Non-protein part

Holoenzyme

Apoenzyme + Cofactor

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Factors Affecting Enzyme Activity

• Temperature

• pH

• Substrate concentration

• Enzyme concentration

• Presence of inhibitors

Optimum Temperature

Around 37°C in humans.

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Vitamins

Vitamins are organic compounds required in small quantities for normal metabolism.

Fat-Soluble Vitamins

• Vitamin A

• Vitamin D

• Vitamin E

• Vitamin K

Water-Soluble Vitamins

• Vitamin B Complex

• Vitamin C

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Biomolecules Found in Living Cells

Micromolecules

Low molecular weight:

• Amino acids

• Monosaccharides

• Nucleotides

Macromolecules

High molecular weight:

• Proteins

• Polysaccharides

• Nucleic acids

Exception

Lipids are macromolecular in function but not true polymers.

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Important NCERT Points for NEET

1. Biomolecules are obtained after acid hydrolysis of tissues.

2. Proteins, nucleic acids, and polysaccharides are true macromolecules.

3. Lipids are not polymers.

4. Enzymes are biological catalysts.

5. ATP is known as the energy currency of the cell.

6. DNA contains thymine, while RNA contains uracil.

7. Cellulose is the most abundant organic compound.

8. Glycogen is the storage carbohydrate in animals.

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Quick NEET Revision Table

Biomolecule	Monomer	Main Function
Carbohydrates	Monosaccharides	Energy source
Proteins	Amino Acids	Structure & enzymes
Lipids	Fatty Acids + Glycerol	Energy storage
DNA	Nucleotides	Genetic information
RNA	Nucleotides	Protein synthesis

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Conclusion

Biomolecules are the foundation of life and play vital roles in cellular structure, metabolism, growth, and heredity. A strong understanding of carbohydrates, proteins, lipids, nucleic acids, and enzymes is essential for scoring well in NEET Biology. Focus on NCERT terminology, classifications, structures, and important examples for effective preparation.