Biomolecules: Complete Class 11 Biology Notes EETfor N

 Biomolecules are the chemical compounds that form the structural and functional basis of living organisms. Every cell contains carbohydrates, proteins, lipids, nucleic acids, vitamins, and other organic molecules that participate in metabolism, growth, repair, and reproduction. The Biomolecules chapter is one of the most important units in Class 11 Biology and carries significant weight in NEET and board examinations.

What are biomolecules?

Biomolecules are carbon-containing compounds synthesized by living organisms. They are broadly classified into:

• Carbohydrates

• Proteins

• Lipids

• Nucleic acids

• Vitamins

Most biomolecules are organic compounds containing carbon, hydrogen, oxygen, and often nitrogen, phosphorus, or sulfur.

Carbohydrates

Carbohydrates are the primary source of energy in living organisms.

General formula

(CH₂O)ₙ

Classification of carbohydrates

Monosaccharides

Simple sugars that cannot be hydrolyzed further.

Examples:

• Glucose

• Fructose

• Galactose

• Ribose

Disaccharides

Formed by the condensation of two monosaccharides.

Examples:

• Sucrose

• Maltose

• Lactose

Polysaccharides

Long chains of monosaccharides.

Examples:

• Starch

• Glycogen

• Cellulose

• Chitin

Functions of carbohydrates

• Immediate source of energy

• Energy storage

• Structural components of cell walls

• Components of nucleic acids

Proteins

Proteins are polymers of amino acids linked by peptide bonds.

Amino acids

An amino acid contains:

• Amino group (–NH₂)

• Carboxyl group (–COOH)

• Hydrogen atom

• Variable R group

There are 20 common amino acids found in proteins.

Levels of protein structure

Primary structure

Linear sequence of amino acids.

Secondary structure

• Alpha helix

• Beta pleated sheet

Tertiary structure

Three-dimensional folding of a polypeptide chain.

Quaternary structure

Association of two or more polypeptide chains.

Functions of proteins

• Enzymes

• Hormones

• Antibodies

• Structural proteins

• Transport proteins

• Contractile proteins

Examples include hemoglobin, collagen, insulin, and actin.

Lipids

Lipids are hydrophobic organic molecules.

Types of lipids

Simple lipids

• Fats

• Oils

• Waxes

Compound lipids

• Phospholipids

• Glycolipids

Derived lipids

• Steroids

• Cholesterol

Structure of fats

Fats are esters of glycerol and fatty acids.

Saturated vs unsaturated fatty acids

Saturated fatty acids

• No double bonds

• Usually solid at room temperature

Unsaturated fatty acids

• One or more double bonds

• Usually liquid at room temperature

Functions of lipids

• Long-term energy storage

• Insulation

• Cell membrane formation

• Hormone synthesis

Nucleic acids

Nucleic acids store and transmit genetic information.

Types

• DNA (Deoxyribonucleic acid)

• RNA (Ribonucleic acid)

Components of a nucleotide

• Nitrogenous base

• Pentose sugar

• Phosphate group

Nitrogenous bases

Purines

• Adenine

• Guanine

Pyrimidines

• Cytosine

• Thymine (DNA)

• Uracil (RNA)

DNA structure

DNA is a double-helical molecule with:

• Complementary base pairing

• Antiparallel strands

Base pairing:

• A = T

• G ≡ C

RNA

RNA is generally single-stranded.

Types of RNA

mRNA

Carries genetic information from DNA to ribosomes.

tRNA

Transfers amino acids during protein synthesis.

rRNA

Forms the structural and catalytic component of ribosomes.

Enzymes

Enzymes are biological catalysts that accelerate biochemical reactions.

Characteristics of enzymes

• Protein in nature

• Highly specific

• Reusable

• Effective in small quantities

Mechanism of enzyme action

Substrate binds to the enzyme’s active site forming the enzyme-substrate complex.

E + S → ES → E + P

Factors affecting enzyme activity

• Temperature

• pH

• Substrate concentration

• Enzyme concentration

• Presence of inhibitors

Vitamins

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

Fat-soluble vitamins

• Vitamin A

• Vitamin D

• Vitamin E

• Vitamin K

Water-soluble vitamins

• Vitamin B complex

• Vitamin C

Common deficiency diseases

Vitamin	Deficiency disease
A	Night blindness
D	Rickets
C	Scurvy
B₁	Beriberi
K	Delayed blood clotting

Biomolecules in metabolism

Biomolecules participate in:

• Glycolysis

• Krebs cycle

• Oxidative phosphorylation

• Protein synthesis

• DNA replication

ATP serves as the universal energy currency of the cell.

Important NCERT and NEET facts

• Proteins are polymers of amino acids.

• Peptide bonds link amino acids.

• DNA contains deoxyribose sugar.

• RNA contains uracil instead of thymine.

• Cellulose is the most abundant organic compound on Earth.

• Enzymes are mostly proteins.

• Cholesterol is a steroid lipid.

Conclusion

Biomolecules are essential for the structure, function, and regulation of living organisms. Carbohydrates provide energy, proteins perform catalytic and structural functions, lipids form membranes and store energy, and nucleic acids preserve genetic information. A strong understanding of biomolecules forms the foundation for advanced topics such as metabolism, genetics, molecular biology, and biotechnology.

Academic references

1. NCERT. Biology, Class XI. National Council of Educational Research and Training, New Delhi.

2. Nelson DL, Cox MM. Lehninger Principles of Biochemistry. 8th ed. W.H. Freeman; 2021.

3. Berg JM, Tymoczko JL, Gatto GJ, Stryer L. Biochemistry. 9th ed. W.H. Freeman; 2019.

4. Alberts B, et al. Molecular Biology of the Cell. 7th ed. Garland Science; 2022.

5. Voet D, Voet JG. Biochemistry. 5th ed. Wiley; 2023.