Full Organic Chemistry Short Notes (Part 4) – Biomolecules | Class 12 & JEE 2026

⭐ Biomolecules – Complete Short Notes (Class 12 & JEE 2026)

Biomolecules are organic compounds that form the basis of life. All living organisms—from bacteria to humans—are made up of these essential molecules. This chapter includes carbohydrates, amino acids, proteins, enzymes, vitamins, nucleic acids, and hormones.

Below is a complete, clear explanation of all concepts.

🔵 1. Carbohydrates

Carbohydrates are optically active polyhydroxy aldehydes (aldoses) or ketones (ketoses), or compounds that produce these units upon hydrolysis.

Examples: glucose, fructose, sucrose, starch, cellulose.

⭐ Types of Carbohydrates

✔ 1. Monosaccharides

Single sugar units like:

Glucose
Fructose
Ribose

All naturally occurring monosaccharides belong to the D-series.

✔ 2. Disaccharides

Formed by joining two monosaccharides.

Examples:

Sucrose → glucose + fructose
Lactose → glucose + galactose
Maltose → glucose + glucose

Note:

Lactose and maltose are reducing sugars.
Sucrose is non-reducing.

✔ 3. Polysaccharides

Large macromolecules made of many monosaccharide units.

Examples:

Starch – polymer of α-glucose
Cellulose – polymer of β-glucose
Glycogen – animal starch

Starch composition:

Amylose (20%) – unbranched, water-soluble
Amylopectin (80%) – branched, water-insoluble
Turns blue with iodine.

⭐ Sweet vs Non-sweet Sugars

Monosaccharides + disaccharides (except sucrose) → sweet & reducing
Polysaccharides → non-sweet & non-reducing

🔵 2. Important Concepts in Carbohydrates

⭐ (A) Kiliani Synthesis

Used to convert an aldose into the next higher aldose.

⭐ (B) Anomers

Cyclic monosaccharides that differ in configuration at:

C-1 (in aldoses)
C-2 (in ketoses)

Example: α-D-glucose and β-D-glucose.

⭐ (C) Mutarotation

The change in optical rotation when α and β forms interconvert through open chain form.

Values :

α-D-glucose → +111.5°
β-D-glucose → +19.5°
Equilibrium mixture → +52.5°

⭐ (D) Epimers

Monosaccharides that differ at one carbon atom other than the anomeric carbon.
Example:

Glucose & galactose differ at C-4 → epimers

⭐ (E) Osazone Formation

Monosaccharides react with phenylhydrazine to form osazones.
Glucose, fructose, and mannose give the same osazone.

🔵 3. Tests for Carbohydrates

Important tests for identifying carbohydrates:

Molisch's test → positive for all carbohydrates
Iodine test → positive for starch & glycogen
Benedict’s test → reducing sugars
Barfoed’s test → distinguishes monosaccharides from disaccharides
Seliwanoff’s test → ketones (like fructose)
Osazone test → crystal shape identifies sugar

🔵 4. Amino Acids

Amino acids contain –NH₂ (amino) and –COOH (carboxyl) groups.

⭐ Types of Amino Acids

✔ Neutral Amino Acids

1 amino group + 1 carboxyl group
Example: glycine

✔ Acidic Amino Acids

1 amino + 2 carboxyl groups
Example: aspartic acid

✔ Basic Amino Acids

2 or more amino groups
Example: lysine

✔ Essential vs Non-essential Amino Acids

Essential: not synthesized by the body
Non-essential: synthesized by the body

🔵 5. Peptides & Proteins

When amino acids join through –CO–NH– linkage (peptide bond), they form peptides.

A polypeptide made of n amino acids has (n–1) peptide bonds.

⭐ Types of Proteins

✔ (A) Fibrous Proteins

Long thread-like
Held by H-bonds & disulphide bonds
Insoluble in water
Example: keratin

✔ (B) Globular Proteins

Spherical
Water soluble
Examples: insulin, albumin

✔ (C) Simple Proteins

Give only amino acids on hydrolysis.

✔ (D) Conjugated Proteins

Give amino acids + a non-protein part (prosthetic group).

✔ (E) Derived Proteins

Formed by partial hydrolysis.

⭐ Protein Denaturation

Any change in the 3D structure of a protein is called denaturation.
Example: cooking an egg.

🔵 6. Tests for Proteins

Important protein tests:

Test Name	Observation
Biuret Test	Violet/pink colour
Millon’s Test	Red colour
Iodine Test	Yellow colour
Xanthoproteic Test	Yellow → orange on adding NaOH

🔵 7. Enzymes

Enzymes are biological catalysts that speed up biochemical reactions.
Examples: pepsin, trypsin

🔵 8. Vitamins

Organic compounds required for growth and good health.

✔ Fat-Soluble Vitamins

A, D, E, K

✔ Water-Soluble Vitamins

B-complex, C

✔ Vitamin H

Neither fat-soluble nor water-soluble

🔵 9. Nucleic Acids (DNA & RNA)

Two important nucleic acids:

⭐ A. DNA (Deoxyribonucleic Acid)

Hydrolysis gives:

Phosphoric acid
Deoxyribose
Bases: A, G, C, T

⭐ B. RNA (Ribonucleic Acid)