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Biomolecules NEET Biology Notes 2026 | Complete NCERT-Based Chapter Notes
Biomolecules NEET Biology Notes provides complete NCERT-based coverage of carbohydrates, proteins, lipids, nucleic acids, enzymes, metabolism, and biomacromolecules. These notes include important definitions, classifications, bond types, high-yield NEET facts, mnemonics, and exam-oriented concepts for quick revision and better understanding of one of the most important Biology chapters.
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Biomolecules NEET Biology Notes are essential for understanding the chemical basis of life and mastering an important chapter for NEET preparation. This chapter covers carbohydrates, proteins, lipids, nucleic acids, enzymes, metabolism, and biomacromolecules in a simple and exam-focused manner. Since conceptual and factual questions are frequently asked about Biomolecules, learning key definitions, classifications, functions, and high-yield facts can significantly improve accuracy and performance in the NEET examination.
Biomolecules NEET Notes: Biomolecules are the fundamental units of life and play a crucial role in all biological processes. This topic is essential for NEET aspirants, as it helps them understand the structure, function, and significance of carbohydrates, proteins, lipids, nucleic acids, and enzymes. Following the cancellation of the NEET UG 2026 exam, affected candidates are now preparing for the re-examination scheduled for June 21, 2026; admit cards for the same have already been released. These notes facilitate quick and effective revision to reinforce key concepts ahead of the re-examination.
1. What Are Biomolecules?
Biomolecules are organic compounds found in living tissues. They are broadly divided into micromolecules (low molecular weight - amino acids, monosaccharides, nucleotides, fatty acids) and macromolecules (high molecular weight, formed by polymerisation of micromolecules - proteins, polysaccharides, nucleic acids, lipids).
Key facts NEET likes to test:
- Living tissue analyzed chemically shows the same elements as non-living matter (C, H, O, N, P, S, etc.) - there is no element unique to living systems.
- On a "per cent dry weight" basis, Proteins are the most abundant biomolecules in living cells on a dry weight basis, but in terms of single compound abundance, cellulose is the most abundant organic compound (and carbohydrate) on Earth, while water remains the most abundant chemical substance in a cell.
- Acid-insoluble fraction of cell extract = macromolecules (proteins, nucleic acids, polysaccharides, lipids). Acid-soluble pool = micromolecules.
2. Primary and Secondary Metabolites
| Feature | Primary Metabolites | Secondary Metabolites |
|---|---|---|
| Role | Direct role in growth, development, reproduction | No obvious/direct role in growth; ecological/defensive role |
| Examples | Amino acids, sugars, nucleic acids, proteins | Alkaloids, flavonoids, rubber, essential oils, antibiotics, pigments, terpenoids |
| Distribution | Universal in all organisms | Species/group specific |
NEET tip: Secondary metabolites like morphine, caffeine, nicotine, vincristine, abrin, concanavalin A, pigments (anthocyanin), essential oils (limonene), polymeric substances (rubber, gums), drugs (vinblastine) are often asked as matching/MCQ.
3. Biomacromolecules - General Concept
- Macromolecules are largely polymers built of repeating monomeric units joined by covalent bonds.
- They are found in the acid insoluble fraction.
- Lipids, though "small," are placed loosely with macromolecules in NCERT because they are found in the acid-insoluble fraction along with proteins, polysaccharides and nucleic acids - even though lipids are NOT true polymers (no repeating monomer-polymer covalent linkage forming one giant molecule).
4. Carbohydrates
Classification by size:
- Monosaccharides (single sugar unit, cannot be hydrolysed further)
- Trioses (C3): glyceraldehyde
- Pentoses (C5): ribose, deoxyribose
- Hexoses (C6): glucose, fructose, galactose
- Oligosaccharides (2–10 monosaccharide units joined by glycosidic bonds)
- Disaccharides: sucrose (glucose + fructose), maltose (glucose + glucose), lactose (glucose + galactose)
- Reducing and Non-Reducing Sugars:
- Reducing sugars: Glucose, Fructose, Lactose, Maltose
- Non-reducing sugar: Sucrose
- Polysaccharides (long chains of monosaccharides)
- Storage: starch (plants), glycogen (animals/fungi), inulin
- Structural: cellulose (plant cell wall), chitin (exoskeleton of arthropods, fungal cell wall)
Important points for NEET:
- Glucose exists in open-chain and ring (Haworth) forms; α and β forms differ in OH orientation at C1 (anomeric carbon).
- Starch gives a blue-black color with iodine; cellulose does not.
- Cellulose is a polymer of β-D-glucose (unbranched), while starch and glycogen are polymers of α-D-glucose.
- Glycogen is more branched than starch (the amylopectin component of starch is branched; amylose is unbranched/helical).
- Bond linking monosaccharides = glycosidic bond (formed by dehydration/condensation).
5. Proteins
- Proteins are polymers of amino acids linked by peptide bonds.
- 20 amino acids are commonly found in proteins (standard set).
- Amino acid = central carbon (Cα) attached to: amino group (–NH₂), carboxyl group (–COOH), hydrogen (–H), and a variable R-group (side chain).
Classification of amino acids:
| Basis | Types |
|---|---|
| Nutritional requirement | Essential (must come from diet, e.g., leucine, lysine, valine) vs Non-essential (body can synthesise, e.g., alanine, glycine) |
| Nature of R group | Acidic (e.g., glutamic acid), Basic (e.g., lysine), Neutral/Polar (e.g., serine), Aromatic (e.g., tyrosine, phenylalanine, tryptophan) |
Peptide bond: formed between the –COOH of one amino acid and –NH₂ of another, with loss of water (dehydration/condensation reaction).
Levels of Protein Structure:
| Level | Description |
|---|---|
| Primary | Linear sequence of amino acids in a polypeptide chain (like alphabets in a sentence) |
| Secondary | Folding of polypeptide into regular repeating shapes – α-helix and β-pleated sheet, stabilised by hydrogen bonds |
| Tertiary | 3-D folding of the secondary structure giving the overall compact shape; essential for biological activity |
| Quaternary | Two or more polypeptide chains (subunits) assemble together, e.g., haemoglobin has 4 subunits (2α + 2β) |
Classification by shape:
- Fibrous proteins: elongated, thread-like (e.g., collagen, keratin) — structural role.
- Globular proteins: folded into a spherical shape (e.g., enzymes, insulin) — functional role.
Protein Denaturation:
- Loss of the native three-dimensional structure of a protein due to heat, extreme pH, chemicals, etc.
- Primary structure remains intact, but secondary, tertiary and quaternary structures are disrupted.
Example: Coagulation of egg white on heating.
NEET fact check: Insulin was the first protein to be sequenced (by Frederick Sanger). Collagen is the most abundant protein in the animal world (mammals); RuBisCO is the most abundant protein in the biosphere (plant world).
6. Lipids
Lipids are a heterogeneous group of compounds, generally insoluble in water, soluble in organic solvents.
| Type | Examples / Structure |
|---|---|
| Simple lipids (fats/oils) | Glycerol + 3 fatty acids (triglyceride) joined by ester bonds |
| Compound/Complex lipids |
Phospholipids (glycerol + 2 fatty acids + phosphate group, e.g., lecithin - major component of cell membrane)
|
| Derived lipids | Steroids (cholesterol), waxes |
Fatty acids:
- Saturated fatty acids - no double bond between carbons, generally solid at room temp (e.g., palmitic acid, stearic acid; found in butter, ghee).
- Unsaturated fatty acids - one or more double bonds, generally liquid at room temp (e.g., oleic acid, linoleic acid; found in vegetable oils).
NEET tip: Cholesterol is a steroid, not a true lipid in the classical sense but classified with lipids; it's a precursor for steroid hormones, bile acids, and vitamin D.
7. Nucleic Acids
Nucleic acids are polymers of nucleotides, linked by phosphodiester bonds.
A nucleotide has 3 components:
- Nitrogenous base (Purine: Adenine, Guanine; Pyrimidine: Cytosine, Thymine, Uracil)
- Pentose sugar (Ribose in RNA; Deoxyribose in DNA)
- Phosphate group
Nucleoside = base + sugar only (no phosphate). Nucleotide = base + sugar + phosphate.
| Feature | DNA | RNA |
|---|---|---|
| Sugar | Deoxyribose | Ribose |
| Bases | A, T, G, C | A, U, G, C |
| Strand | Usually double-stranded (double helix) | Usually single-stranded |
| Function | Genetic material, hereditary information | mRNA, tRNA, rRNA - protein synthesis; genetic material in some viruses |
- Base pairing in DNA: A=T (2 hydrogen bonds), G≡C (3 hydrogen bonds) - Chargaff's rule.
- Bond between adjacent nucleotides = phosphodiester bond (between sugar of one nucleotide and phosphate of next).
8. Nature of Bond Linking Monomers - Quick Table
| Macromolecule | Monomer | Bond |
|---|---|---|
| Polysaccharide | Monosaccharide | Glycosidic bond |
| Protein | Amino acid | Peptide bond |
| Nucleic acid | Nucleotide | Phosphodiester bond |
| Fat/Triglyceride | Glycerol + fatty acid | Ester bond |
9. Dynamic State of Body Constituents - Concept of Metabolism
- All biomolecules in a cell undergo continuous turnover (synthesis and breakdown) - this is the metabolic pool / dynamic state.
- Anabolism: building up larger molecules from smaller ones (biosynthesis) requires energy.
- Catabolism: breakdown of larger molecules into smaller ones, releases energy.
- Metabolic pathways are interconnected — a metabolite can move between several pathways.
- Thousands of metabolic reactions occur simultaneously in a cell, all catalysed by enzymes - this is the "metabolic basis of living."
10. The Living State
- Living organisms exist in a steady state - a non-equilibrium state with constant exchange of energy/matter, distinguishing life from non-living matter, which tends toward equilibrium (maximum entropy/disorder).
- Order, not equilibrium, characterizes the living state. Maintaining the concentration of metabolites at optimum levels for life is the living state.
11. Enzymes
Definition: Enzymes are biological catalysts, mostly proteins (some RNA molecules called ribozymes also act as catalysts), that speed up biochemical reactions without being consumed.
Properties:
- Highly specific to substrate.
- Increase reaction rate without altering equilibrium.
- Active only within a range of temperature and pH.
- Required in small/catalytic amounts.
Classification of enzymes (6 major classes) - frequently asked:
| Class | Function | Example |
|---|---|---|
| Oxidoreductases | Catalyse oxidation-reduction between two substrates | Dehydrogenases |
| Transferases | Transfer a group (other than H) from one substrate to another | Transaminases |
| Hydrolases | Catalyse hydrolysis (transfer of group to water) | Amylase, Lipase |
| Lyases | Remove groups without hydrolysis, forming double bonds | Decarboxylases |
| Isomerases | Catalyse the interconversion of optical/geometric isomers | Phosphohexose Isomerase |
| Ligases | Join two molecules using ATP energy | DNA Ligase |
Mechanism of enzyme action:
- Substrate binds at the active site of the enzyme → forms the enzyme-substrate (ES) complex.
- Product forms and is released; the enzyme is regenerated and reused.
- Two models explain binding: the Lock and Key model (rigid fit) and the Induced Fit model (active site changes shape to accommodate substrate - currently accepted model).
Factors affecting enzyme activity:
- Temperature: activity increases with temperature up to an optimum, then declines (denaturation) — bell-shaped curve.
- pH: each enzyme has an optimum pH; activity declines on either side.
- Substrate concentration: rate increases with substrate concentration until it plateaus (saturation, all active sites occupied).
- Enzyme concentration: rate generally increases with enzyme concentration if the substrate is in excess.
- Inhibitors:
- Competitive inhibition: inhibitor resembles substrate, competes for active site (e.g., malonate inhibits succinic dehydrogenase).
- Non-competitive inhibition: inhibitor binds elsewhere, changes enzyme shape, not reversed by raising substrate concentration.
Cofactors (non-protein helpers required for enzyme activity):
| Type | Description | Example |
|---|---|---|
| Prosthetic group | Tightly/permanently bound organic molecule | Haem in catalase/peroxidase |
| Co-enzyme | Loosely bound organic molecule, often derived from vitamins | NAD, NADP, FAD (from vitamin B) |
| Metal ions | Inorganic ion forming coordination bonds | Zn²⁺ in carboxypeptidase |
Holoenzyme = Apoenzyme (protein part) + Cofactor
12. High-Yield Quick Facts for NEET (often directly asked)
- Most abundant biomolecule in a cell: Water.
- The most abundant carbohydrate in nature is cellulose.
- Most abundant protein in the biosphere: RuBisCO.
- Most abundant protein in the animal kingdom: Collagen.
- Number of standard amino acids: 20.
- The double helix model of DNA was proposed by Watson and Crick (1953).
- Enzyme classification body: International Union of Biochemistry and Molecular Biology (IUBMB).
- Ribozymes = RNA molecules with catalytic (enzymatic) activity.
- Glycosidic, peptide, phosphodiester, and ester bonds are all formed by dehydration (condensation) reactions and broken by hydrolysis.
13. One-Page Mnemonic / Memory Aids
- Bonds: "Glyco-Sugar, Pepti-Protein, Phospho-Nucleic, Ester-Fat" — match the bond type to its macromolecule.
- DNA bases: "Pure As Gold" → Purines = Adenine, Guanine (double-ringed); Pyrimidines = Cytosine, Thymine, Uracil (single-ringed).
- Enzyme classes order: "Old Teachers Help Lazy Intelligent Learners "
- O = Oxidoreductase
- T = Transferase
- H = Hydrolase
- L = Lyase
- I = Isomerase
- L = Ligase
Important Links
Conclusion - Biomolecules Biology Notes
Biomolecules NEET Biology Notes are an excellent resource for mastering the molecular foundation of life and strengthening NEET Biology preparation. By thoroughly understanding carbohydrates, proteins, lipids, nucleic acids, enzymes, metabolism, and important biomolecular interactions, students can confidently solve conceptual and factual questions. Regular revision of these Biomolecules NEET Biology Notes, along with NCERT examples and high-yield facts, can help improve accuracy, retention, and overall NEET performance.
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