NCERT Class 12 Chemistry Chapter 10 Biomolecules Notes PDF

Ans. Chapter 10 Biomolecules carries 3 to 5 marks in the CBSE Class 12 Chemistry board exam, averaged across the last five board papers. The marks usually split as one 2-mark structure or difference question (DNA vs RNA, alpha-helix vs beta-sheet, mutarotation) plus a 2- or 3-mark classification or test question. NEET expands this to 3 to 5 questions per year, making the chapter much higher-value for dual-prep students.

Ans. Four core differences. Sugar: DNA has deoxyribose (no -OH at C2); RNA has ribose (-OH at C2 - hence less stable). Bases: DNA uses A, G, C, T; RNA replaces thymine with uracil (A, G, C, U). Structure: DNA is a right-handed double helix held by A=T (2 H-bonds) and G≡C (3 H-bonds), antiparallel strands; RNA is normally single-stranded but folds back on itself in tRNA and rRNA. Function: DNA stores hereditary information and replicates; mRNA carries the genetic message, tRNA delivers amino acids, rRNA forms the ribosome.

Ans. Reducing sugars must have a free anomeric -OH (the -OH on the carbon that was originally the carbonyl) so they can open back to the aldehyde or ketone form and reduce Tollens or Fehling reagent. In sucrose, the anomeric C1 of alpha-D-glucose is glycosidically linked to the anomeric C2 of beta-D-fructose; neither anomeric -OH is free. Without a free aldehyde/hemiacetal, sucrose cannot reduce Cu(II) or Ag(I). On acid hydrolysis, the two halves separate, each regains a free anomeric -OH, and both products (glucose and fructose) become individually reducing.

Ans. (i) Primary structure - the exact linear sequence of amino acids joined by peptide bonds (one mistake here can cause sickle-cell anaemia). (ii) Secondary structure - local folding via -C=O...H-N- hydrogen bonds: alpha-helix (right-handed coil, 3.6 residues/turn, in keratin and myoglobin) and beta-pleated sheet (parallel or antiparallel strands, in silk fibroin). (iii) Tertiary structure - overall 3-D fold of one chain, stabilised by disulphide bridges, salt bridges, hydrogen bonds, and van der Waals (myoglobin, lysozyme). (iv) Quaternary structure - assembly of two or more polypeptide subunits (haemoglobin = 2 alpha + 2 beta chains).

Ans. Essential amino acids cannot be synthesised by the human body in sufficient amounts and must come from the diet. There are 10 of them in the standard list followed by NCERT: Valine, Leucine, Isoleucine, Threonine, Lysine, Methionine, Phenylalanine, Tryptophan, Histidine, and Arginine. (Histidine and Arginine are sometimes called semi-essential, since adults can make limited amounts; growing children need them in the diet.) The remaining 10 of the 20 standard amino acids are non-essential and are synthesised in the body.

Ans. Vitamins are organic micronutrients required in small amounts for normal metabolism. Fat-soluble vitamins (A, D, E, K) are stored in the liver; water-soluble vitamins (B-complex and C) are not stored. Key deficiency diseases: A - night-blindness, xerophthalmia; B₁ - beri-beri; B₂ - cheilosis, glossitis; B₆ - convulsions, anaemia; B₁₂ - pernicious anaemia; C - scurvy; D - rickets (children), osteomalacia (adults); E - sterility, muscular weakness; K - poor blood clotting.

Ans. Yes. This page reflects the current 2026-27 syllabus for Class 12 Chemistry. The new NCERT edition keeps the full five-section Biomolecules chapter intact - carbohydrates, proteins, enzymes, vitamins, and nucleic acids - while the rationalisation drive removed the Hormones sub-section. All NCERT in-text and exercise questions remain in the 2026-27 print and are covered in our linked Solutions page.

Ans. The Notes PDF runs approximately 22 pages and covers all five NCERT sections of Chapter 10 Biomolecules: carbohydrates (classification, glucose / fructose structure, glycosidic linkage, starch / cellulose / glycogen), proteins (amino acids, zwitterion, peptide bond, four structure levels, denaturation), enzymes (mechanism, specificity, optimum conditions), vitamins (fat- vs water-soluble, deficiency diseases), and nucleic acids (DNA, RNA, base pairing, double helix, replication). Every structure is illustrated with a colour-coded diagram, and every test (Tollens, Fehling, Molisch, Benedict, iodine, Biuret) is tabulated for easy recall.

Ans. You can download the complete 22-page Class 12 Chemistry Chapter 10 Biomolecules Notes PDF for free from the download card at the top of this page. Both Normal and HD versions are available. The PDF follows the 2026-27 NCERT print and includes the full carbohydrate hierarchy (mono- / oligo- / poly-saccharides), the alpha-amino-acid grid, all four protein-structure levels, the vitamin deficiency chart, the DNA vs RNA difference wall, and the six classical biomolecule tests stacked on a single revision page.

Ans. Both terms describe stereoisomers of sugars, but they differ in where the chirality switches. Anomers differ only at the anomeric carbon (C1 in aldoses, C2 in ketoses), the new chiral centre created on cyclisation. Alpha- and beta-D-glucopyranose are the canonical anomers (-OH below or above the ring plane at C1). Epimers differ at one non-anomeric chiral centre. Glucose and galactose are C4 epimers; glucose and mannose are C2 epimers. The interconversion of anomers in solution is called mutarotation; the equilibrium mixture for glucose averages to a specific rotation of +52.5 degrees.

Ans. Purines are double-ring nitrogen bases - adenine (A) and guanine (G); mnemonic "PURe As Gold". Pyrimidines are single-ring bases - cytosine (C), thymine (T) and uracil (U). DNA contains A, G, C, and T (uracil is absent in DNA); RNA contains A, G, C, and U (thymine is replaced by uracil). In the DNA double helix the Watson-Crick base pairs are A ··· T (2 H-bonds) and G ··· C (3 H-bonds); each pair is one purine plus one pyrimidine so the ring sizes match perfectly across the helix.

Ans. The alpha-helix is a right-handed coil with 3.6 amino acid residues per turn, stabilised by intra-chain hydrogen bonds between the -N-H of residue i and the -C=O of residue i+4 along the same strand. The H-bonds run roughly parallel to the helix axis. A beta-pleated sheet is built from extended (not coiled) strands held together by inter-chain hydrogen bonds between the -N-H of one strand and the -C=O of an adjacent strand; the strands can be parallel or antiparallel. Examples - alpha-helix is found in keratin (hair), myoglobin and the alpha-helical portions of haemoglobin; beta-pleated sheets are found in silk fibroin and the beta-keratin of feathers and scales.

Ans. Insulin is a polypeptide hormone produced by the beta-cells of the pancreas. Its primary structure consists of two polypeptide chains - the A chain with 21 residues and the B chain with 30 residues - held together by two inter-chain disulphide (-S-S-) bridges and one intra-chain disulphide bridge within the A chain. Total length is 51 amino acids and molecular mass is about 5,800 u. Although insulin is below the conventional 100-residue boundary that separates polypeptides from proteins, its well-defined three-dimensional fold and dedicated biological function (lowering blood glucose by promoting cellular uptake and storage as glycogen) earn it the status of a protein hormone. It belongs to the polypeptide / protein class of hormones; the other two classes are steroid (cholesterol-derived) and amino-acid-derived (thyroxine, epinephrine).

Ans. Memorise the fat-soluble set first - the four ADEK vitamins are stored in the liver and adipose tissue. Then memorise five disease-vitamin pairs that NCERT highlights: A → night blindness / xerophthalmia; B₁ → beri-beri; B₁₂ → pernicious anaemia; C → scurvy; D → rickets / osteomalacia; K → poor blood clotting. NEET has tested at least one of these pairs every year since 2021. The trap CBSE plays - swapping B₁ (beri-beri) with B₁₂ (pernicious anaemia) - is easily defused by remembering "1 = beri" and "12 = cobalt-amin = anaemia".