The 2026-27 NCERT keeps Chapter 10 Biomolecules intact, with all five sections covering carbohydrates, proteins, enzymes, vitamins, and nucleic acids. This page hosts the latest Notes PDF, the Haworth-projection walk, the alpha-helix vs beta-sheet contrast, and the DNA / RNA comparison built for the 2026 boards.
- CBSE Boards: 3 to 5 marks every year, usually a 2-mark structure question (mutarotation, peptide bond, alpha-helix) plus a 2- or 3-mark classification or DNA-RNA difference problem.
- JEE Main: 1 to 2% of the Chemistry paper, with 1 question per shift on carbohydrate classification, amino-acid zwitterion, or DNA base pairing.
- NEET: 3 to 5 questions per year on protein structure, enzyme catalysis, vitamin deficiency diseases, and nucleotide composition.
The article below carries the carbohydrate classification tree, the alpha-amino-acid grid, all four protein-structure levels, the vitamin deficiency chart, and the DNA vs RNA wall.
These Collegedunia Biomolecules notes are curated by subject experts, mapped to the 2026-27 NCERT print, and refined against the last five years of CBSE Board, JEE Main, and NEET papers.
Also Check:
- Biomolecules Class 12 Chemistry NCERT Solutions
- Biomolecules Class 12 Chemistry Formula Sheet
- CBSE Class 12 Chemistry Syllabus 2026-27
Why Biomolecules Matters for Class 12 Boards, JEE Main, and NEET 2026-27
Biomolecules is the bio-organic chapter of Class 12 Chemistry, the bridge from textbook organic into pharmacology, biotechnology, and medicine. For NEET aspirants it overlaps directly with Class 11 Biology Ch 9 (Biomolecules) and Class 12 Biology Ch 6 (Molecular Basis of Inheritance), making the chapter a high-yield revision target.
In 4 of the last 5 NEET papers, at least 3 questions came directly from this single Chemistry chapter.
Biomolecules Video Walkthrough
Source: Magnet Brains on YouTube
How will Collegedunia's NCERT Notes Help You with Biomolecules?
The Collegedunia Biomolecules Notes give you four wins students lose marks on: a side-by-side Haworth vs Fischer projection table for glucose and fructose (the trap CBSE has set 3 of the last 5 years), the 20 alpha-amino-acid one-letter grid with essential / non-essential split, a colour-coded protein-structure ladder (primary → quaternary), and the DNA vs RNA difference wall built for 2-mark CBSE slots.
- 2026-27 NCERT Alignment: Every concept matches the current edition; Hormones is dropped, all five core sections intact.
- Structure Walk-Throughs: Haworth projection of alpha-D-glucose, beta-D-glucose, alpha-D-fructose with axial / equatorial labels.
- Test Map: Tollens, Fehling, Molisch, Benedict, Iodine, and Biuret tests stacked into one table.
- Quick Revision Strip: Each section ends with a yellow recall strip and a tiny formula box.
Biomolecules Topic-by-Topic Notes for Class 12 Chemistry
Each block below maps to a numbered NCERT section in the 2026-27 print.
Sections 10.1 and 10.5 together carry roughly 4 marks every CBSE year. Lock the carbohydrate hierarchy and the DNA-RNA difference table first.
Anomers, Epimers and Mutarotation - The Stereochemistry Triad of Section 10.1
Three terms that students confuse routinely. Locking them in saves at least one 2-mark CBSE question every year.
- Anomers: stereoisomers that differ only at the anomeric carbon (C1 in aldoses, C2 in ketoses). The anomeric carbon is the new chiral centre created when the open chain cyclises. Glucose has two anomers - alpha-D-glucopyranose (-OH below the ring at C1) and beta-D-glucopyranose (-OH above the ring).
- Epimers: stereoisomers that differ at one non-anomeric chiral centre. Glucose and galactose are C4 epimers; glucose and mannose are C2 epimers. Do not call them anomers.
- Mutarotation: the gradual change in optical rotation of a freshly dissolved pure anomer as it equilibrates with the other anomer via the open-chain form. Glucose: pure alpha = +112 degrees, pure beta = +19 degrees, equilibrium = +52.5 degrees.
Carbohydrate Classification Tree - Section 10.1 Recall Grid
The carbohydrate tree is the spine of Section 10.1. CBSE has tested "classify the following: glucose, sucrose, starch, cellulose" in 3 of the last 5 years.
| Class | Hydrolysis behaviour | NCERT examples | Taste / property |
|---|---|---|---|
| Monosaccharides | Cannot be hydrolysed further | Glucose (aldohexose), fructose (ketohexose), ribose, galactose | Sweet, water-soluble, all reducing |
| Oligosaccharides (2-10 units) | Hydrolyse to monosaccharides | Disaccharides: sucrose, maltose, lactose | Sweet, soluble; reducing depends on free anomeric -OH |
| Polysaccharides (>10 units) | Hydrolyse to many monosaccharides | Starch (storage in plants), cellulose (structural in plants), glycogen (storage in animals) | Tasteless, water-insoluble, non-reducing |
Alpha-Helix vs Beta-Pleated Sheet - Why the H-Bond Pattern Matters
The secondary-structure trap CBSE / NEET asks every alternate year. Both are stabilised by H-bonds between the peptide -C=O and -N-H, but the pattern is different.
| Feature | Alpha-helix | Beta-pleated sheet |
|---|---|---|
| Coil / sheet | Right-handed coil | Extended pleated strands |
| H-bond direction | Intra-chain (within the same strand) | Inter-chain (between adjacent strands) |
| H-bond rule | -N-H of residue i to -C=O of residue i+4 | -N-H of one strand to -C=O of the next strand |
| Strand orientation | Single chain | Parallel or antiparallel |
| Residues per turn / repeat | 3.6 residues per turn; rise 5.4 angstroms | ~7 angstroms repeat per dipeptide |
| Examples | Keratin (hair, nails), myoglobin, alpha portion of haemoglobin | Silk fibroin, beta-keratin (feathers, scales) |
Vitamins, Sources and Deficiency Diseases - Section 10.4 Recall Strip
NEET asks one vitamin-deficiency MCQ almost every year since 2021. The nine-vitamin grid below is the canonical NCERT Table 10.3 reformat.
| Vitamin | Solubility | Source | Deficiency disease |
|---|---|---|---|
| A (retinol) | Fat-soluble | Fish liver oil, carrots, butter | Night blindness, xerophthalmia |
| B1 (thiamine) | Water-soluble | Yeast, milk, cereals | Beri-beri |
| B2 (riboflavin) | Water-soluble | Milk, egg white, liver | Cheilosis, glossitis |
| B6 (pyridoxine) | Water-soluble | Yeast, milk, egg yolk | Convulsions, anaemia |
| B12 (cobalamin) | Water-soluble (but stored in liver) | Meat, fish, egg, curd | Pernicious anaemia |
| C (ascorbic acid) | Water-soluble | Citrus fruits, amla, leafy vegetables | Scurvy, bleeding gums |
| D (calciferol) | Fat-soluble | Sunlight, fish, egg yolk | Rickets (children), osteomalacia (adults) |
| E (tocopherol) | Fat-soluble | Wheat germ oil, sunflower oil | RBC fragility, muscular weakness, sterility |
| K (phylloquinone) | Fat-soluble | Green leafy vegetables | Increased blood clotting time |
Purines vs Pyrimidines and the DNA-RNA Difference Wall - Section 10.5
The two ring-class families of nitrogen bases are tested as a 1-mark MCQ in almost every NEET paper.
- Purines (two fused rings): Adenine (A) and Guanine (G). Mnemonic: "PURe As Gold".
- Pyrimidines (single ring): Cytosine (C), Thymine (T), Uracil (U). Thymine is found only in DNA; uracil is found only in RNA; cytosine is in both.
- Nucleoside vs Nucleotide: nucleoside = base + sugar (no phosphate); nucleotide = base + sugar + phosphate. Only nucleotides polymerise to nucleic acids through 5'-3' phosphodiester linkages.
- Watson-Crick base pairing: A ··· T via 2 H-bonds, G ··· C via 3 H-bonds; the pair size matches because each pair is one purine + one pyrimidine. Chargaff's rule: A = T and G = C in any DNA sample.
- RNA types: mRNA (carries the genetic message from DNA), tRNA (transfers amino acids), rRNA (structural component of the ribosome). All three are single-stranded.
Hormones and Their Chemical Classes - Section 10.6 Outline
The 2026-27 NCERT trimmed the detailed hormone discussion but retains the three-class outline. Useful for assertion-reason items.
- Steroid hormones: derived from cholesterol; examples - estrogens (female), testosterone (male), cortisol (stress), aldosterone (mineral balance).
- Polypeptide / protein hormones: chains of amino acids. Insulin is the textbook example (51 amino acids in two chains held by -S-S- bridges, lowers blood glucose); glucagon (29 AA) raises blood glucose.
- Amino-acid-derived hormones: Thyroxine (iodinated tyrosine, low levels cause goitre and hypothyroidism), epinephrine / adrenaline (fight-or-flight).
Biomolecules Class 12 Topic-wise Weightage for CBSE Boards
The marks below average CBSE, JEE Main, and NEET papers from 2021 to 2025.
| Sub-Topic | Section | CBSE Marks | Frequency |
|---|---|---|---|
| Carbohydrate classification & structure | 10.1 | 2 - 3 | Very High |
| DNA vs RNA, base pairing | 10.5 | 2 - 3 | Very High |
| Protein structure (primary to quaternary) | 10.2 | 1 - 2 | High |
| Vitamins & deficiency diseases | 10.4 | 1 - 2 | High |
| Enzymes and catalysis | 10.3 | 1 | Medium |
| Amino acids, zwitterion, isoelectric pt | 10.2 | 1 | Medium |
Sections 10.1 and 10.5 deliver the bulk of the chapter band; 10.2 and 10.4 pick up the remainder.
Class 12 Chemistry Ch 10 Important Tests, Structures and Difference Tables
The six tests below cover every carbohydrate / protein identification CBSE has asked since 2021.
| Test | Reagent | Positive For → Observation |
|---|---|---|
| Molisch test | alpha-naphthol, conc. H2SO4 | All carbohydrates → violet ring |
| Tollens test | [Ag(NH3)2]+OH- | Reducing sugars → silver mirror |
| Fehling test | Cu2+ tartrate, NaOH | Reducing sugars → red Cu2O ppt |
| Benedict test | Cu2+ citrate, Na2CO3 | Reducing sugars → orange-red ppt |
| Iodine test | I2 in KI | Starch → blue-black; glycogen → red-brown |
| Biuret test | NaOH + dilute CuSO4 | Proteins (peptide bonds) → violet colour |
CBSE has framed "Identify A using a single test" using this reagent grid in 3 of the last 5 board papers.
Important Structures and Comparisons in 12th Chemistry Chapter 10
The PDF carries five fully-worked structures and contrast tables; these are the ones most likely in CBSE 2-mark and 3-mark slots.
- Open-chain ↔ cyclic glucose: aldehyde at C1 attacks C5-OH → hemiacetal; new chiral centre at C1 gives alpha (axial -OH) and beta (equatorial -OH) anomers. Appeared in CBSE 2024, 2022.
- Sucrose hydrolysis (invert sugar): sucrose +H2O / dil. HCl → glucose + fructose; rotation swings +66 → -20. Appeared in CBSE 2025, 2023.
- Peptide bond formation: -COOH of one amino acid + -NH2 of next, loses H2O; planar amide link, partial double-bond character. Appeared in CBSE 2024, 2021.
- Alpha-helix vs beta-sheet: helix - intrachain H-bond between -C=O of n and -N-H of n+4; sheet - interchain H-bond, pleated, parallel or antiparallel. Appeared in CBSE 2025, 2022.
- DNA double helix & replication: two antiparallel strands (5' → 3' and 3' → 5'), A=T (2H), G≡C (3H), semiconservative replication splits the strands. Appeared in CBSE 2023, NEET 2024.
Frequently Asked Biomolecules Questions in CBSE Board Exams (2021 to 2026)
Three PYQ-style stems CBSE has favoured since 2021. The structures and tables repeat.
Q1 (CBSE 2025, 3 marks): (i) Define mutarotation. (ii) Why is sucrose called invert sugar but is itself non-reducing? (iii) Give one chemical test to distinguish glucose from fructose.
A: (i) Mutarotation = the change in optical rotation when a pure anomer of a sugar dissolves in water and equilibrates to a mixture of alpha and beta forms via the open-chain aldehyde. Glucose: +112 → +52.5. (ii) Sucrose itself has no free anomeric -OH (C1 of glucose and C2 of fructose are both in the glycosidic link), so it does not reduce Tollens or Fehling. On hydrolysis, the rotation inverts from +66 to -20 (glucose +52.5 + fructose -92), hence "invert sugar". (iii) Seliwanoff test (resorcinol + conc. HCl): fructose gives red colour in <1 min, glucose gives a fainter colour only on longer heating.
Q2 (CBSE 2024, 2 marks): Differentiate between DNA and RNA on the basis of (i) sugar, (ii) bases, (iii) structure, (iv) function.
A: (i) DNA - deoxyribose (no 2'-OH); RNA - ribose (2'-OH). (ii) DNA - A, G, C, T; RNA - A, G, C, U. (iii) DNA - double helix, antiparallel; RNA - single-stranded (folds back in tRNA, rRNA). (iv) DNA - stores hereditary information, replicates; RNA - mRNA carries the message, tRNA brings amino acids, rRNA forms ribosomes.
Q3 (CBSE 2023, 3 marks): What are the four levels of protein structure? Give one example for each.
A: (i) Primary - the sequence of amino acids linked by peptide bonds (e.g. insulin A-chain has 21 residues in a fixed order). (ii) Secondary - local folding stabilised by H-bonds, alpha-helix (keratin in hair) or beta-pleated sheet (silk fibroin). (iii) Tertiary - overall 3-D fold of a single chain held by disulphide, ionic, H-bonds, van der Waals (myoglobin). (iv) Quaternary - association of two or more polypeptide chains (haemoglobin: 2 alpha + 2 beta subunits).
Biomolecules Top 5 Formulae and Facts for Quick Recall
The five facts you should memorise first for any Class 12 Biomolecules paper. The complete master sheet lives on the Formula Sheet.
| # | Concept | Formula / Statement |
|---|---|---|
| 1 | Glucose & Fructose | C6H12O6; glucose = aldohexose, fructose = ketohexose. Both reducing. |
| 2 | Sucrose hydrolysis | Sucrose + H2O → D-glucose + D-fructose; +66o → -20o (invert sugar). |
| 3 | Zwitterion | H3N+-CHR-COO-; net charge 0 at isoelectric point (pI). |
| 4 | DNA base pairing | A = T (2 H-bonds), G ≡ C (3 H-bonds); Chargaff: A=T, G=C. |
| 5 | Essential amino acids | 10 total: Val, Leu, Ile, Thr, Lys, Met, Phe, Trp, His, Arg (mnemonic: "PVT TIM HALL" + Arg). |
Full master table: Biomolecules Class 12 Chemistry Formula Sheet
Real-World Applications of Biomolecules
Why biomolecules matter beyond the exam paper.
- Medicine & Diagnostics: Insulin (a protein) treats diabetes; glycated haemoglobin HbA1c is the standard 3-month diabetes marker; PCR amplifies DNA for COVID and forensic tests.
- Food Science: Lactose intolerance is the absence of lactase enzyme; invert sugar (sucrose hydrolysed) is the base of honey, soft drinks, and jam preservation.
- Biotechnology: Restriction enzymes cut DNA at specific sites; recombinant insulin, vaccines, and monoclonal antibodies are commercial proteins; mRNA technology powers the COVID-19 vaccines.
- Nutrition: Vitamin deficiencies cause classical diseases - scurvy (C), rickets (D), beri-beri (B1), night-blindness (A); food fortification (iodised salt, iron in flour) closes population-level gaps.
Full year-wise PYQ map: Biomolecules Class 12 Chemistry NCERT Solutions
Class 12 Chemistry Chapter 10 Weightage Compared Across All Chapters
Each bar is the chapter's average CBSE mark count from 2021 to 2025.
Ch 10 sits at 4 marks for boards but spikes to 3 to 5 questions in NEET. For dual-prep students it is one of the highest-ROI chapters in the Class 12 Chemistry syllabus.
More Biomolecules Chemistry Class 12 Resources
- Class 12 Chemistry Chapter 10 Biomolecules NCERT Solutions
- Class 12 Chemistry Chapter 10 Biomolecules Formula Sheet
- Class 12 Chemistry Chapter 10 Biomolecules NCERT Book PDF
- Class 12 Chemistry Chapter 10 Biomolecules Handwritten Notes
- Class 12 Chemistry Chapter 10 Biomolecules Exemplar Solutions
- Class 12 Chemistry Chapter 10 Biomolecules Exemplar Book PDF
NCERT Notes for Class 12 Chemistry: All Chapters
Continue revising the rest of the Class 12 Chemistry NCERT with the chapter-wise Notes library below.
| Chapter | Notes Page |
|---|---|
| Chapter 1 | Solutions Notes |
| Chapter 2 | Electrochemistry Notes |
| Chapter 3 | Chemical Kinetics Notes |
| Chapter 4 | The d- and f-Block Elements Notes |
| Chapter 5 | Coordination Compounds Notes |
| Chapter 6 | Haloalkanes and Haloarenes Notes |
| Chapter 7 | Alcohols, Phenols and Ethers Notes |
| Chapter 8 | Aldehydes, Ketones and Carboxylic Acids Notes |
| Chapter 9 | Amines Notes |
Biomolecules Class 12 Chemistry Notes FAQs
Ques. How many marks does Chapter 10 Biomolecules carry in the CBSE Class 12 board exam?
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.
Ques. What is the difference between DNA and RNA?
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.
Ques. Why is sucrose called a non-reducing sugar despite containing both glucose and fructose?
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.
Ques. What are the four levels of protein structure?
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).
Ques. What are essential amino acids? Name them.
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.
Ques. What are vitamins and which diseases are caused by their deficiency?
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.
Ques. Is this Biomolecules Notes PDF aligned with the 2026-27 NCERT?
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.
Ques. How many pages is the Class 12th Chemistry Biomolecules Notes PDF?
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.
Ques. Where can I download the Class 12 Chemistry Chapter 10 Biomolecules notes PDF for free?
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 is mapped to 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.
Ques. What are anomers and epimers, and how do they differ from each other?
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.
Ques. What is the difference between purines and pyrimidines, and which bases are found in DNA and RNA?
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.
Ques. How is the alpha-helix stabilised in proteins and how does it differ from a beta-pleated sheet?
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.
Ques. What is insulin and why is it classified as a protein hormone?
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).
Ques. How do you remember the vitamin-deficiency pairs quickly?
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".
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