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Master Biomolecules for NEET 2026 with detailed notes on carbohydrates, proteins, lipids, nucleic acids, and enzymes. NCERT-aligned content with diagrams and previous year questions.
Remember these points for your NEET preparation
Biomolecules chapter contributes 4-6 questions in NEET and forms the foundation for understanding biochemistry. This guide covers all NCERT concepts essential for NEET 2026.
Living organisms are made up of various chemical compounds called biomolecules. These can be classified as:
| Category | Examples | Characteristics |
|---|---|---|
| Micromolecules | Sugars, amino acids, nucleotides | Low molecular weight, simple |
| Macromolecules | Proteins, nucleic acids, polysaccharides | High molecular weight, polymers |
Primary vs Secondary Metabolites:
Cn(H2O)n - hence the name "hydrates of carbon"
| Sugar | Carbon atoms | Example | Source |
|---|---|---|---|
| Triose | 3C | Glyceraldehyde | Glycolysis intermediate |
| Tetrose | 4C | Erythrose | Pentose phosphate pathway |
| Pentose | 5C | Ribose, Deoxyribose | RNA, DNA |
| Hexose | 6C | Glucose, Fructose, Galactose | Most common |
Important Hexoses:
| Disaccharide | Components | Bond | Source |
|---|---|---|---|
| Sucrose | Glucose + Fructose | α-1,2 | Sugarcane, beetroot |
| Maltose | Glucose + Glucose | α-1,4 | Germinating seeds |
| Lactose | Glucose + Galactose | β-1,4 | Milk |
NEET Tip: Sucrose is a non-reducing sugar because both anomeric carbons are involved in the glycosidic bond.
| Polysaccharide | Monomer | Bond Type | Function |
|---|---|---|---|
| Starch | α-glucose | α-1,4 (amylose), α-1,4 & α-1,6 (amylopectin) | Plant storage |
| Glycogen | α-glucose | α-1,4 & α-1,6 (more branched) | Animal storage |
| Cellulose | β-glucose | β-1,4 | Plant cell wall |
| Chitin | N-acetylglucosamine | β-1,4 | Fungal cell wall, exoskeleton |
Key Difference: Starch and glycogen are digestible; cellulose is not (humans lack cellulase enzyme).
General Structure:
Classification by R Group:
| Type | Property | Examples |
|---|---|---|
| Non-polar | Hydrophobic | Glycine, Alanine, Valine, Leucine |
| Polar uncharged | Hydrophilic | Serine, Threonine, Asparagine |
| Acidic | Negatively charged | Aspartic acid, Glutamic acid |
| Basic | Positively charged | Lysine, Arginine, Histidine |
| Aromatic | Ring structure | Phenylalanine, Tyrosine, Tryptophan |
Essential Amino Acids (must be obtained from diet): Mnemonic - PVT TIM HALL
| Level | Description | Bonds Involved |
|---|---|---|
| Primary | Linear sequence of amino acids | Peptide bonds |
| Secondary | α-helix, β-pleated sheet | Hydrogen bonds |
| Tertiary | 3D folding | H-bonds, ionic, disulfide, hydrophobic |
| Quaternary | Multiple polypeptide chains | Same as tertiary |
Examples:
Fatty Acids:
| Type | Structure | Examples | Property |
|---|---|---|---|
| Saturated | No double bonds | Palmitic, Stearic | Solid at room temp |
| Unsaturated | Double bonds present | Oleic (1), Linoleic (2) | Liquid at room temp |
Triglycerides (Fats & Oils):
| Type | Components | Example | Function |
|---|---|---|---|
| Phospholipids | Glycerol + 2 FA + Phosphate | Lecithin | Cell membrane |
| Glycolipids | Lipid + Carbohydrate | Cerebrosides | Cell recognition |
| Lipoproteins | Lipid + Protein | LDL, HDL | Lipid transport |
Nucleotide = Nitrogenous base + Pentose sugar + Phosphate group
Nitrogenous Bases:
| Purines (Double ring) | Pyrimidines (Single ring) |
|---|---|
| Adenine (A) | Cytosine (C) |
| Guanine (G) | Thymine (T) - DNA only |
| Uracil (U) - RNA only |
Base Pairing Rules (Chargaff's Rules):
| Feature | DNA | RNA |
|---|---|---|
| Sugar | Deoxyribose | Ribose |
| Bases | A, T, G, C | A, U, G, C |
| Structure | Double-stranded | Usually single-stranded |
| Location | Nucleus, mitochondria, chloroplast | Nucleus, cytoplasm, ribosomes |
| Function | Genetic information storage | Protein synthesis |
| Type | Function | Location |
|---|---|---|
| mRNA | Carries genetic code | Nucleus → Cytoplasm |
| tRNA | Transfers amino acids | Cytoplasm |
| rRNA | Component of ribosomes | Ribosomes |
Biological catalysts that speed up reactions without being consumed.
| Class | Reaction Type | Example |
|---|---|---|
| Oxidoreductases | Oxidation-reduction | Dehydrogenases |
| Transferases | Transfer of groups | Kinases |
| Hydrolases | Hydrolysis | Lipases, Proteases |
| Lyases | Non-hydrolytic removal | Decarboxylases |
| Isomerases | Isomerization | Mutases |
| Ligases | Bond formation using ATP | Synthetases |
| Factor | Effect |
|---|---|
| Temperature | Increases to optimum, then denatures |
| pH | Optimal pH varies (pepsin: 2, trypsin: 8) |
| Substrate concentration | Increases until saturation |
| Enzyme concentration | Directly proportional |
| Inhibitors | Competitive or non-competitive |
| Type | Mechanism | Effect on Km | Effect on Vmax |
|---|---|---|---|
| Competitive | Binds to active site | Increases | Unchanged |
| Non-competitive | Binds elsewhere | Unchanged | Decreases |
| Type | Nature | Examples |
|---|---|---|
| Prosthetic group | Tightly bound | Heme in hemoglobin |
| Co-enzyme | Loosely bound, organic | NAD⁺, FAD, Coenzyme A |
| Metal ion | Inorganic | Zn²⁺, Mg²⁺, Fe²⁺ |
Q1 (NEET 2023): Which of the following is a non-reducing sugar?
Q2 (NEET 2022): The most abundant protein in the animal world is:
Q3 (NEET 2021): Which of the following is an example of pyrimidine?
Q4 (NEET 2020): Competitive inhibitor of an enzyme:
Q5 (NEET 2019): Essential amino acids are those which:
Q: Why is sucrose called a non-reducing sugar? A: In sucrose, both anomeric carbons (C1 of glucose and C2 of fructose) are involved in the glycosidic bond, so there's no free aldehyde or ketone group to reduce other compounds.
Q: What makes an amino acid essential? A: Essential amino acids cannot be synthesized by the human body in sufficient quantities and must be obtained from the diet. There are 9 essential amino acids for adults.
Q: Why do enzymes have optimal temperature and pH? A: Enzymes are proteins with specific 3D structures. Temperature and pH changes can alter hydrogen bonds and ionic interactions that maintain this structure. Beyond optimal conditions, the enzyme denatures and loses activity.
Q: What is the difference between DNA and RNA in terms of stability? A: DNA is more stable because: (1) deoxyribose lacks 2'-OH making it less reactive, (2) double-stranded structure provides redundancy, (3) thymine instead of uracil prevents deamination errors.
Q: Why is RuBisCO considered the most abundant protein? A: RuBisCO (Ribulose-1,5-bisphosphate carboxylase/oxygenase) is found in all photosynthetic organisms and makes up about 50% of leaf protein. Given the vast amount of plant biomass on Earth, it's the most abundant protein globally.
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