Biomolecules is a high-weightage chapter in NEET Chemistry (Class 12, Chapter 14) contributing 3u20134 questions annually. It covers carbohydrates, proteins, lipids, nucleic acids, and enzymes u2014 all from biological systems. With the right approach, this is a scoring chapter that can be mastered in 3u20134 study sessions.
NEET Biomolecules u2014 Chapter Snapshot
| Parameter | Details |
|---|---|
| Class | 12 |
| Chapter | 14 u2014 Biomolecules |
| NEET Avg. Questions | 3u20134 per year |
| Difficulty | Moderate (definitions + application) |
| Key Topics | Carbohydrates, Proteins, Nucleic Acids, Enzymes |
Carbohydrates u2014 NEET Notes
Classification
| Type | Examples | Key Fact |
|---|---|---|
| Monosaccharides | Glucose, Fructose, Galactose | Cannot be hydrolysed further |
| Disaccharides | Sucrose (glucose+fructose), Maltose, Lactose | Formed by glycosidic bond |
| Polysaccharides | Starch, Glycogen, Cellulose | Storage or structural function |
Key NEET distinctions:
- Starch = plant storage; Glycogen = animal storage (“animal starch”)
- Cellulose = structural in plant cell walls; NOT digestible by humans
- Glucose is both aldose (CHO group) u2014 reducing sugar; Fructose is ketose
- Sucrose is a non-reducing sugar u2014 no free aldehyde/ketone group
Proteins u2014 NEET Notes
Four Levels of Protein Structure
| Level | Description | Bonds/Forces |
|---|---|---|
| Primary | Sequence of amino acids in polypeptide chain | Peptide bonds (covalent) |
| Secondary | u03b1-helix or u03b2-pleated sheet arrangement | Hydrogen bonds |
| Tertiary | 3D folding of entire polypeptide | H-bonds, disulfide bridges, ionic, hydrophobic |
| Quaternary | Multiple polypeptide chains combined | Same as tertiary (e.g., haemoglobin has 4 chains) |
Denaturation = loss of 3D structure (secondary/tertiary/quaternary) without breaking peptide bonds. Reversible or irreversible. Caused by heat, acid, pH change.
Enzymes u2014 Critical for NEET
Key Enzyme Concepts
- Enzymes are proteins (except ribozymes which are RNA)
- Active site: specific region that binds substrate (lock and key model)
- Induced fit model: active site changes shape when substrate binds (more accurate)
- Enzymes lower activation energy u2014 they are not consumed
- Cofactors: metal ions (Znu00b2u207a, Feu00b2u207a) needed by some enzymes
- Coenzymes: organic cofactors (NADu207a, FAD u2014 vitamin-derived)
- Apoenzyme + cofactor = holoenzyme (active enzyme)
Enzyme Inhibition Types
| Type | Inhibitor Binding | Effect on Km/Vmax |
|---|---|---|
| Competitive | Active site (competes with substrate) | u2191Km, Vmax unchanged |
| Non-competitive | Allosteric site (changes enzyme shape) | Km unchanged, u2193Vmax |
| Feedback inhibition | End product inhibits enzyme | Regulatory mechanism |
Nucleic Acids u2014 DNA vs RNA
| Feature | DNA | RNA |
|---|---|---|
| Sugar | Deoxyribose | Ribose |
| Bases | A, T, G, C | A, U, G, C (Uracil instead of Thymine) |
| Strands | Double-stranded (usually) | Single-stranded (usually) |
| Location | Nucleus (primarily) | Nucleus + Cytoplasm |
| Function | Stores genetic info | Protein synthesis (mRNA, tRNA, rRNA) |
Practice Quiz u2014 NEET Biomolecules
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FAQ
Is Biomolecules important for NEET 2027?
Yes. Biomolecules (Class 12 Chemistry Chapter 14) typically contributes 3u20134 questions. It is a memory-based chapter with moderate difficulty. 2 days of focused revision with NCERT + previous year questions is sufficient to score full marks from this chapter.
What is the difference between lock and key model and induced fit model?
Lock and key model (Emil Fischer) says the active site is rigid and the substrate fits exactly like a key in a lock. The induced fit model (Koshland) is more accurate u2014 it proposes the enzyme’s active site flexibly adjusts its shape when the substrate binds.
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