Scope: High-yield NCERT-based facts, structures, reactions, definitions and diagrams for JEE Main. Learn structures and exceptions exactly as given in NCERT.
Biomolecules
├── Carbohydrates: monosaccharides → oligosaccharides → polysaccharides
├── Proteins: amino acids → peptides → polypeptides/proteins
├── Enzymes: biological catalysts
├── Vitamins: organic micronutrients
└── Nucleic acids: nucleotides → DNA/RNA
Carbohydrates: Polyhydroxy aldehydes or ketones, or substances that yield them on hydrolysis.
Monosaccharides: Cannot be hydrolysed into simpler carbohydrates. Examples: glucose, fructose, ribose.
Oligosaccharides: Give 2–10 monosaccharide units on hydrolysis. Disaccharides are the most important.
Polysaccharides: Give a large number of monosaccharide units on hydrolysis. Examples: starch, cellulose, glycogen.
Aldose: Carbohydrate containing an aldehyde group.
Ketose: Carbohydrate containing a ketone group.
Glucose: C₆H₁₂O₆; aldohexose.
Fructose: C₆H₁₂O₆; ketohexose.
Ribose: C₅H₁₀O₅.
Deoxyribose: C₅H₁₀O₄.
General approximate formula: Cₓ(H₂O)ᵧ — not valid for every carbohydrate.
Open-chain structure contains five –OH groups and one aldehyde group.
On prolonged heating with HI, glucose gives n-hexane, showing an unbranched six-carbon chain.
With hydroxylamine, glucose forms an oxime; with HCN, a cyanohydrin: evidence for a carbonyl group.
Mild oxidation gives gluconic acid; strong oxidation gives saccharic/glucaric acid.
Glucose + Br₂ water → gluconic acid.
Glucose + HNO₃ → saccharic (glucaric) acid.
Reduction with HI/red P ultimately gives n-hexane.
D/L notation refers to configuration relative to glyceraldehyde, not optical rotation.
(+) / (−) denotes direction of optical rotation.
CHO
|
H — C — OH C2: OH right
|
OH— C — H C3: OH left
|
H — C — OH C4: OH right
|
H — C — OH C5: OH right
|
CH2OH
C1 aldehyde reacts intramolecularly with C5 –OH to form a hemiacetal.
Six-membered cyclic form is glucopyranose.
α-D-glucose: anomeric OH at C1 is opposite to CH₂OH group.
β-D-glucose: anomeric OH at C1 is on the same side as CH₂OH group in Haworth representation.
Anomers: Stereoisomers differing only at the anomeric carbon.
Mutarotation: Change in optical rotation due to interconversion of α- and β-forms through the open-chain form.
α-D-glucopyranose ⇌ open-chain glucose ⇌ β-D-glucopyranose
Fructose is a ketohexose and usually forms a five-membered cyclic fructofuranose hemiacetal/hemiketal form.
Its carbonyl group is at C2.
Fructose is a reducing sugar in alkaline medium because it can tautomerise through an enediol to aldoses.
Sugar | Hydrolysis products | Linkage | Reducing? |
|---|---|---|---|
Sucrose, C₁₂H₂₂O₁₁ | Glucose + fructose | α-D-glucose C1 — O — C2 fructose (α,β-1→2) | Non-reducing |
Maltose, C₁₂H₂₂O₁₁ | Glucose + glucose | α(1→4) | Reducing |
Lactose, C₁₂H₂₂O₁₁ | Galactose + glucose | β(1→4) | Reducing |
Hydrolysis of sucrose gives invert sugar; the hydrolysate’s rotation changes from positive to negative.
In sucrose, both anomeric carbons participate in the glycosidic bond, so it is non-reducing.
In maltose and lactose, one anomeric carbon remains free, so they are reducing sugars.
Starch: Polymer of α-D-glucose; plant storage polysaccharide. Components: amylose (mostly linear α(1→4)) and amylopectin (branched α(1→4), α(1→6)). Gives blue colour with iodine.
Glycogen: Highly branched storage polysaccharide in animals; α-D-glucose units.
Cellulose: Linear polymer of β-D-glucose with β(1→4) linkages; structural material in plants; humans cannot digest it due to absence of cellulase.
Chitin: Nitrogen-containing polysaccharide made from N-acetylglucosamine; found in insect exoskeletons.
Amino acid: Compound containing amino and carboxyl groups; proteins mainly contain α-amino acids.
General structure:
H
|
H₂N — C — COOH
|
R
Zwitterion: Dipolar ion formed by internal proton transfer:
⁺H₃N — CH(R) — COO⁻
Zwitterions explain the high melting points and water solubility of amino acids.
Amino acids are generally amphoteric and have an isoelectric point (pI) at which net charge is zero.
Acidic amino acid: Extra –COOH group; e.g., aspartic acid, glutamic acid.
Basic amino acid: Extra basic amino group; e.g., lysine, arginine.
Neutral amino acid: Equal number of acidic and basic groups; e.g., glycine, alanine.
Essential amino acids: Must be obtained through diet; examples include valine, leucine, lysine and methionine.
Non-essential amino acids: Can be synthesised by the body.
Formed by condensation between –COOH of one amino acid and –NH₂ of another, with loss of H₂O.
—COOH + H₂N— → —CO—NH— + H₂O
peptide bond
Dipeptide: Two amino acid units; one peptide bond.
Tripeptide: Three amino acid units; two peptide bonds.
Polypeptide: Long chain of amino acids.
For a linear chain of n amino acids, peptide bonds = n − 1, and water molecules eliminated = n − 1.
A protein may contain one or more polypeptide chains.
Primary structure: Exact sequence of amino acids; represented from N-terminus to C-terminus.
Secondary structure: Local folding; mainly α-helix and β-pleated sheet, stabilised by hydrogen bonds.
Tertiary structure: Overall three-dimensional folding of one polypeptide chain; interactions include hydrogen bonds, ionic interactions, van der Waals forces and disulfide bonds.
Quaternary structure: Spatial arrangement of multiple polypeptide subunits.
Primary: —AA—AA—AA—AA—
Secondary: α-helix / β-pleated sheet
Tertiary: compact 3-D folding
Quaternary: several folded subunits together
Fibrous proteins: Long, thread-like, generally insoluble; structural role. Example: keratin, collagen.
Globular proteins: Spherical/compact, generally soluble; functional role. Examples: insulin, albumin, haemoglobin.
Denaturation: Loss of secondary, tertiary and/or quaternary structure without breaking the primary structure.
Causes: heat, pH change, chemicals, heavy-metal salts.
Denatured protein generally loses biological activity.
Coagulation: Irreversible denaturation/precipitation in many cases, e.g., cooking of egg white.
Renaturation may occur in limited cases if the denaturing condition is removed.
Biuret test: Peptide bonds + Cu²⁺ in alkaline medium → violet/ purple colour.
Xanthoproteic test: Aromatic amino acids + concentrated HNO₃ → yellow colour, deepened by alkali.
Ninhydrin test: α-amino acids generally give blue/purple colour; proline gives a yellow colour.
Enzymes: Biological catalysts, mostly globular proteins; some catalytic RNA molecules are ribozymes.
They are highly efficient and generally highly specific.
Enzymes work best at an optimum temperature and optimum pH.
Excessive temperature or extreme pH can denature enzymes.
Substrate: Molecule on which enzyme acts.
Active site: Specific region of an enzyme where substrate binds.
Enzyme action:
E + S ⇌ ES → E + P
enzyme + substrate ⇌ enzyme–substrate complex → enzyme + product
Enzymes lower activation energy and do not alter the equilibrium constant or overall ΔG of a reaction.
Lock-and-key model: Rigid complementarity between active site and substrate.
Induced-fit model: Active site adjusts shape on substrate binding.
Temperature: increases rate up to optimum; then activity falls due to denaturation.
pH: maximum activity at optimum pH.
Substrate concentration: rate rises and then approaches a maximum when active sites are saturated.
Inhibitors: decrease enzyme activity.
Vitamins: Organic compounds required in small amounts for normal growth and health; usually not synthesised sufficiently by the body.
Fat-soluble: A, D, E, K — stored in body fat; excess may cause toxicity.
Water-soluble: B-complex and C — generally not stored extensively; regular intake is important.
Vitamin | Chemical name / key association | Deficiency disease or effect |
|---|---|---|
A | Retinol | Night blindness, xerophthalmia |
B₁ | Thiamine | Beriberi |
B₂ | Riboflavin | Cheilosis, skin disorders |
B₃ | Niacin | Pellagra |
B₆ | Pyridoxine | Anaemia, skin disorders |
B₁₂ | Cyanocobalamin | Pernicious anaemia |
C | Ascorbic acid | Scurvy |
D | Calciferol | Rickets/osteomalacia |
E | Tocopherol | Reproductive/antioxidant-related effects |
K | Phylloquinone | Delayed blood clotting |
Vitamin C is water-soluble and an antioxidant.
Vitamin D helps calcium and phosphorus metabolism.
Vitamins are not a source of energy like carbohydrates, fats and proteins.
Nucleic acids: Polymers of nucleotides; DNA and RNA are the two main types.
Nucleoside: Nitrogenous base + pentose sugar.
Nucleotide: Nitrogenous base + pentose sugar + phosphate group.
Phosphodiester bond: Linkage connecting the 3′-OH of one sugar to the 5′-phosphate of the next nucleotide.
Nitrogenous base + sugar = nucleoside
Nucleoside + phosphate = nucleotide
Nucleotide + nucleotide + ... = nucleic acid
Purines: Adenine (A), guanine (G); double-ring structure.
Pyrimidines: Cytosine (C), thymine (T), uracil (U); single-ring structure.
DNA contains A, G, C, T.
RNA contains A, G, C, U; uracil replaces thymine.
Feature | DNA | RNA |
|---|---|---|
Sugar | 2-deoxyribose | Ribose |
Bases | A, G, C, T | A, G, C, U |
Typical structure | Double-stranded helix | Usually single-stranded |
Main role | Genetic storage | Protein synthesis and other functions |
Two polynucleotide strands are antiparallel: one 5′→3′ and the other 3′→5′.
Sugar-phosphate backbone is on the outside; bases face inward.
Complementary base pairing:
A = T through 2 hydrogen bonds.
G ≡ C through 3 hydrogen bonds.
Chargaff’s rule: In double-stranded DNA, A = T and G = C; therefore purines = pyrimidines.
More G–C pairs generally mean greater thermal stability.
5′ — sugar—phosphate—sugar—phosphate — 3′
A ══ T
G ≡≡≡ C
T ══ A
3′ — phosphate—sugar—phosphate—sugar — 5′
DNA ──transcription──> RNA ──translation──> Protein
Replication: DNA → DNA.
Transcription: DNA → RNA.
Translation: mRNA information → amino-acid sequence.
Number of peptide bonds in a linear protein made of n amino acids = n − 1.
Number of water molecules released during formation of that linear peptide = n − 1.
For a nucleotide chain, adjacent nucleotides are linked by phosphodiester bonds.
In double-stranded DNA: A = T, G = C.
Total hydrogen bonds in DNA = 2 × number of A–T pairs + 3 × number of G–C pairs.
If total base pairs = N and G–C pairs = x, H-bonds = 2(N − x) + 3x = 2N + x.
If DNA has A% = x%, then T% = x%, and G% = C% = (100 − 2x)/2%.
For a monosaccharide, cyclic hemiacetal/hemiketal formation creates an anomeric carbon.
Reducing sugar: has a free anomeric carbon or can generate a free carbonyl group in solution.
Aldose, ketose, monosaccharide, oligosaccharide, polysaccharide, glycosidic linkage, anomer, mutarotation, reducing sugar, invert sugar, zwitterion, amphoteric, isoelectric point, peptide bond, polypeptide, primary structure, α-helix, β-pleated sheet, denaturation, enzyme, active site, substrate, vitamin, nucleoside, nucleotide, purine, pyrimidine, phosphodiester bond, complementary base pairing, antiparallel strands, transcription, translation.
Sucrose is non-reducing because both anomeric carbons are involved in its glycosidic bond.
Maltose and lactose are reducing sugars because one anomeric carbon remains free.
D-glucose is dextrorotatory, but D/L and +/− are different notations.
Fructose is a ketose but behaves as a reducing sugar in alkaline medium.
Denaturation does not normally destroy the primary structure.
Enzymes change the rate, not the equilibrium constant.
DNA has deoxyribose and thymine; RNA has ribose and uracil.
A nucleoside has no phosphate; a nucleotide has at least one phosphate.
A–T has 2 hydrogen bonds; G–C has 3.
Glycosidic linkage joins sugar units; peptide linkage joins amino acids; phosphodiester linkage joins nucleotides.
Draw Fischer and cyclic glucose.
Memorise glucose/fructose formula and classification.
Compare sucrose, maltose and lactose.
Learn starch, glycogen, cellulose and chitin differences.
Count peptide bonds and identify protein structures.
Memorise vitamin names and deficiency diseases.
Distinguish nucleoside, nucleotide and nucleic acid.
Apply Chargaff’s rule and DNA hydrogen-bond counting.
Revise reducing/non-reducing sugars and mutarotation.