JEE Mains Chemistry · Biomolecules
Enzymes and Vitamins
Enzymes are globular-protein catalysts, each specific to one reaction and usually named after its substrate; vitamins split into fat-soluble A, D, E and K, which the body stores, and the water-soluble B group and C, which it excretes (except B12), and each vitamin has one deficiency disease to remember.
Why this matters
Eighteen PYQs, seventeen multiple choice and one asking for a number, two from 2026. Six are on enzymes: what they are, and which enzyme converts which substrate, as match-the-list questions. Four ask which vitamins the body can store. Eight match a vitamin to its chemical name or to its deficiency disease.
Concept 1 of 3: Enzymes and the reaction each one catalyses
An enzyme is a protein catalyst made by a living cell. It speeds up one reaction, on one substrate, at body temperature, by lowering the activation energy far more than an acid catalyst does. Most enzyme names tell you the substrate: maltase acts on maltose, invertase inverts cane sugar.
Definition
- Enzymes are biocatalysts and almost all are globular proteins (NCERT).
- They are highly specific: each catalyses one reaction for one substrate.
- They are usually named after the substrate: the enzyme that hydrolyses maltose to glucose is maltase. Oxidoreductases catalyse the oxidation of one substrate with the reduction of another; an oxidase does not hydrolyse anything.
- They lower the activation energy much more than an acid catalyst: sucrose is hydrolysed with a lower activation energy by its enzyme than by acid.
- The enzyme–substrate pairs in the table, and urease from soya bean, come from the enzyme-catalysis section of NCERT's older Surface Chemistry chapter, not from the Biomolecules text; the other sources are the standard ones.
- As substrate concentration rises, the rate rises and then levels off once every enzyme molecule is busy. This saturation curve is outside NCERT.
| Enzyme | Converts | Into | Source or site |
|---|---|---|---|
| Invertase | Sucrose (cane sugar) | Glucose and fructose | Yeast |
| Zymase | Glucose | Ethanol and carbon dioxide | Yeast |
| Diastase | Starch | Maltose | Malt (germinating barley) |
| Maltase | Maltose | Glucose | Yeast |
| Urease | Urea | Ammonia and carbon dioxide | Soya bean |
| Pepsin | Proteins | Peptides | Stomach |
| Trypsin | Peptides and proteins | Amino acids | Pancreas, acting in the intestine |
Starch goes to maltose (diastase), then to glucose (maltase), then to ethanol (zymase).
Practice this conceptself-check · 4 quick reps
The same idea in a real exam question:
JEE Mains · 2024 · 6 April 2024 · Q123Moderate
Example 1 · Biomolecules · Enzymes and Vitamins
The incorrect statements regarding enzymes are: (A) Enzymes are biocatalysts. (B) Enzymes are non-specific and can catalyse different kinds of reactions. (C) Most Enzymes are globular proteins. (D) Enzyme - oxidase catalyses the hydrolysis of maltose into glucose. Choose the correct answer from the option given below:
Maltase, not oxidase, hydrolyses maltose
Enzymes are named for what they act on. The hydrolysis of maltose to glucose is catalysed by maltase; an oxidase catalyses an oxidation.
Diastase stops at maltose
Diastase converts starch into maltose, not glucose. Maltase takes maltose on to glucose, and zymase takes glucose to ethanol and CO₂.
Enzymes are specific
Each enzyme catalyses one reaction or one class of reaction. A statement that enzymes are non-specific and catalyse different kinds of reactions is false.
Concept 2 of 3: Fat-soluble and water-soluble vitamins: which are stored
Solubility decides storage. Fat-soluble vitamins dissolve in body fat and stay there. Water-soluble vitamins wash out in urine, so the diet must supply them regularly. Vitamin B12 is the one exception: it is water soluble but is stored.
Definition
- Fat-soluble: vitamins A, D, E and K. They are stored in the liver and adipose (fat-storing) tissue.
- Water-soluble: the B group (B1, B2, B6, B12) and vitamin C. They are readily excreted in urine and cannot be stored, so they must be supplied regularly in the diet.
- Exception: vitamin B12 is water soluble but can be stored (NCERT).
- So the vitamins the body can store are A, D, E, K and B12.
Worked example
From vitamins B2, C, D, K, B6 and B12, how many can the body store?
Practice this conceptself-check · 4 quick reps
The same idea in a real exam question:
JEE Mains · 2024 · 31 January 2024 · Q149Moderate
Example 2 · Biomolecules · Enzymes and Vitamins
From the vitamins A, and , the number of vitamins that can be stored in our body is _____
B12 is water soluble but stored
Do not drop B12 when counting storable vitamins. The count is the four fat-soluble vitamins plus B12.
Thiamine and ascorbic acid are not stored
Thiamine is B1 and ascorbic acid is C; both are water soluble. Of the common pairs, vitamins A and D are the ones stored for a long time.
Concept 3 of 3: Vitamins: chemical names, deficiency diseases and sources
Each vitamin has one deficiency disease in the syllabus, and the B vitamins are told apart by their chemical names. Learn the table as pairs; the questions are almost all match-the-list, where one swapped pair changes the answer.
Definition
- The B vitamins by name: B1 thiamine, B2 riboflavin, B6 pyridoxine, B12 cyanocobalamin.
- Ascorbic acid (vitamin C) is the vitamin among common acids; adipic, aspartic and saccharic acid are not vitamins.
- Vitamin K deficiency increases blood clotting time.
- NCERT gives vitamin E deficiency as increased fragility of red blood cells and muscular weakness. A 2021 key says vitamin E delays blood clotting; that is not an NCERT fact.
| Vitamin | Chemical name | Deficiency disease | Main sources |
|---|---|---|---|
| A | Retinol | Xerophthalmia (hardening of the cornea) and night blindness | Fish liver oil, carrots, butter, milk |
| B1 | Thiamine | Beri-beri (loss of appetite, retarded growth) | Yeast, milk, green vegetables, cereals |
| B2 | Riboflavin | Cheilosis (fissures at the corners of the mouth and lips), digestive disorders | Milk, egg white, liver, kidney |
| B6 | Pyridoxine | Convulsions | Yeast, milk, egg yolk, cereals, grams |
| B12 | Cyanocobalamin | Pernicious anaemia | Meat, fish, egg, curd |
| C | Ascorbic acid | Scurvy (bleeding gums) | Citrus fruits, amla, green leafy vegetables |
| D | Calciferol | Rickets in children, osteomalacia in adults | Sunlight, fish, egg yolk |
| E | Tocopherol | Increased fragility of red blood cells, muscular weakness | Vegetable oils such as wheat germ and sunflower oil |
| K | Phylloquinone | Increased blood clotting time | Green leafy vegetables |
B1, B2 and B6 are the pairs most often swapped: thiamine, riboflavin, pyridoxine.
Practice this conceptself-check · 4 quick reps
The same idea in a real exam question:
JEE Mains · 2026 · 6 Apr 2026 Shift 1 · Q44Moderate
Example 3 · Biomolecules · Enzymes and Vitamins
Match List-I with List-II:
Choose the correct answer from the options given below :
| List-I Deficiency Disease | List-II Vitamin | ||
|---|---|---|---|
| (A) | Scurvy | (I) | Pyridoxine |
| (B) | Convulsions | (II) | Vitamin A |
| (C) | Cheilosis | (III) | Ascorbic Acid |
| (D) | Xerophthalmia | (IV) | Riboflavin |
Thiamine, riboflavin, pyridoxine in order
B1 is thiamine, B2 riboflavin and B6 pyridoxine. Their diseases follow the same order: beri-beri, cheilosis, convulsions.
Vitamin K deficiency slows clotting
Without vitamin K blood takes longer to clot, so the clotting time increases. An option saying it decreases is false.
Summary — formulas & gotchas at a glance
A revision cheat-sheet for the formulas and gotchas above. Click any concept name to jump back to its full explanation.
Reference tables (2)
Enzymes and the reaction each one catalyses7 rows
| Enzyme | Converts | Into | Source or site |
|---|---|---|---|
| Invertase | Sucrose (cane sugar) | Glucose and fructose | Yeast |
| Zymase | Glucose | Ethanol and carbon dioxide | Yeast |
| Diastase | Starch | Maltose | Malt (germinating barley) |
| Maltase | Maltose | Glucose | Yeast |
| Urease | Urea | Ammonia and carbon dioxide | Soya bean |
| Pepsin | Proteins | Peptides | Stomach |
| Trypsin | Peptides and proteins | Amino acids | Pancreas, acting in the intestine |
Starch goes to maltose (diastase), then to glucose (maltase), then to ethanol (zymase).
Vitamins: chemical names, deficiency diseases and sources9 rows
| Vitamin | Chemical name | Deficiency disease | Main sources |
|---|---|---|---|
| A | Retinol | Xerophthalmia (hardening of the cornea) and night blindness | Fish liver oil, carrots, butter, milk |
| B1 | Thiamine | Beri-beri (loss of appetite, retarded growth) | Yeast, milk, green vegetables, cereals |
| B2 | Riboflavin | Cheilosis (fissures at the corners of the mouth and lips), digestive disorders | Milk, egg white, liver, kidney |
| B6 | Pyridoxine | Convulsions | Yeast, milk, egg yolk, cereals, grams |
| B12 | Cyanocobalamin | Pernicious anaemia | Meat, fish, egg, curd |
| C | Ascorbic acid | Scurvy (bleeding gums) | Citrus fruits, amla, green leafy vegetables |
| D | Calciferol | Rickets in children, osteomalacia in adults | Sunlight, fish, egg yolk |
| E | Tocopherol | Increased fragility of red blood cells, muscular weakness | Vegetable oils such as wheat germ and sunflower oil |
| K | Phylloquinone | Increased blood clotting time | Green leafy vegetables |
B1, B2 and B6 are the pairs most often swapped: thiamine, riboflavin, pyridoxine.
Watch out for (7)
- Maltase, not oxidase, hydrolyses maltose→ Enzymes and the reaction each one catalyses
- Diastase stops at maltose→ Enzymes and the reaction each one catalyses
- Enzymes are specific→ Enzymes and the reaction each one catalyses
- B12 is water soluble but stored→ Fat-soluble and water-soluble vitamins: which are stored
- Thiamine and ascorbic acid are not stored→ Fat-soluble and water-soluble vitamins: which are stored
- Thiamine, riboflavin, pyridoxine in order→ Vitamins: chemical names, deficiency diseases and sources
- Vitamin K deficiency slows clotting→ Vitamins: chemical names, deficiency diseases and sources
Test yourself on Biomolecules
20 past JEE Mains questions from this chapter, timed at 48 minutes and marked the way the exam marks it. You see your score and every answer the moment you finish. Free to start.