JEE Main Chemistry Biomolecules 2027: Carbohydrates, Proteins, Vitamins & Nucleic Acids
Glucose structure, sucrose, maltose and lactose, protein structure levels, vitamins and DNA versus RNA, with the facts JEE Main tests most often.
Edurack
September 28, 2026
Biomolecules is almost entirely NCERT-driven. There is very little calculation and no long mechanism, which makes it one of the fastest chapters to prepare and one of the most reliable for quick marks when you revise it well.
This chapter rewards the student who has read NCERT twice. Precision beats depth here.
Chapter at a Glance
| Snapshot | Detail |
|---|---|
| NTA unit | Unit 19 of 20: Biomolecules |
| Priority (trend-based) | Moderate |
| Typical question style | Fact-based MCQs from NCERT on structures, linkages and classification |
| Best first step | Read NCERT line by line and make comparison tables |
Priority reflects past-paper trends, not an official NTA weightage.
What the NTA Syllabus Covers
- General introduction and importance of biomolecules
- Carbohydrates: classification, aldoses and ketoses, monosaccharides (glucose and fructose), constituent monosaccharides of sucrose, lactose and maltose
- Proteins: α-amino acids, peptide bond, polypeptides, primary, secondary, tertiary and quaternary structure, denaturation, enzymes
- Vitamins: classification and functions
- Nucleic acids: chemical constitution and biological functions of DNA and RNA; hormones (general introduction)
Master These Topics
1. Carbohydrates
Carbohydrates are polyhydroxy aldehydes or ketones, classified as monosaccharides, oligosaccharides and polysaccharides.
Glucose is an aldohexose (C₆H₁₂O₆), and fructose is a ketohexose. Evidence for glucose's open-chain structure:
- Reacts with HI to give n-hexane, showing a straight six-carbon chain.
- Forms a pentaacetate with acetic anhydride, showing five −OH groups.
- Gives Tollens' and Fehling's tests, showing a free aldehyde.
But glucose does not react with NaHSO₃ or Schiff's reagent, which shows it mainly exists in a cyclic hemiacetal form. Cyclisation creates a new stereocentre, giving α and β anomers, which interconvert in solution (mutarotation).
| Disaccharide | Units | Linkage | Reducing? |
|---|---|---|---|
| Sucrose | α-D-glucose + β-D-fructose | C1 to C2 | No |
| Maltose | Glucose + glucose | α C1 to C4 | Yes |
| Lactose | β-D-galactose + glucose | β C1 to C4 | Yes |
Sucrose is non-reducing because both anomeric carbons are tied up in the glycosidic bond. Hydrolysing sucrose gives an equimolar mixture of glucose and fructose called invert sugar, which is laevorotatory because fructose rotates more strongly to the left than glucose does to the right.
2. Proteins
Amino acids exist as zwitterions, with both −NH₃⁺ and −COO⁻ groups. A peptide bond (−CO−NH−) links amino acids into polypeptides.
| Level | What it is |
|---|---|
| Primary | Sequence of amino acids |
| Secondary | α-helix or β-pleated sheet held by hydrogen bonds |
| Tertiary | Overall 3D folding of one chain |
| Quaternary | Arrangement of multiple chains |
Denaturation destroys the secondary and tertiary structure (for example boiling an egg) without breaking peptide bonds, so the primary structure remains. Enzymes are biological catalysts, mostly proteins, and are highly specific.
Trap: Denaturation does not break peptide bonds. The primary structure is preserved.
3. Vitamins
Fat-soluble: A, D, E, K. Water-soluble: B complex and C. Key deficiency diseases:
- Vitamin A: night blindness
- Vitamin B₁: beri-beri
- Vitamin C: scurvy
- Vitamin D: rickets
- Vitamin K: delayed blood clotting
4. Nucleic Acids
DNA has deoxyribose sugar and bases A, T, G, C in a double helix. RNA has ribose and bases A, U, G, C, and is usually single-stranded (mRNA, tRNA, rRNA).
Base pairing: A pairs with T (two hydrogen bonds) and G pairs with C (three hydrogen bonds). Worked example: If a DNA sample has 30% adenine, it has 30% thymine, and the remaining 40% is split equally between guanine and cytosine (20% each).
Hormones are chemical messengers. Examples include insulin (a protein hormone), adrenaline (an amino acid derivative) and steroid hormones such as oestrogen.
Common Traps to Avoid
- Saying denaturation breaks peptide bonds.
- Calling sucrose a reducing sugar.
- Mixing up the linkage and monomers of maltose, lactose and sucrose.
- Forgetting that RNA has uracil in place of thymine.
60-Second Revision Sheet
- Glucose: aldohexose; fructose: ketohexose; α and β anomers form on cyclisation
- Sucrose non-reducing; maltose and lactose reducing
- Denaturation preserves the primary structure
- A-T two H-bonds; G-C three H-bonds; RNA has uracil
Your Study Plan
- Day 1: carbohydrate classification, glucose evidence and disaccharides.
- Day 2: amino acids, peptide bond and protein structure levels.
- Day 3: vitamins with deficiency diseases, then nucleic acids.
- Day 4: NCERT revision and a timed mixed set.
Practice Biomolecules Questions Free → (opens in a new tab)
Continue Your Chemistry Journey
- Previous chapter: Organic Compounds Containing Nitrogen
- Next chapter: Principles Related to Practical Chemistry
- All JEE Main Chemistry chapters
- Complete JEE Main Syllabus 2027 guide
Frequently Asked Questions
Why is sucrose a non-reducing sugar?
Its glycosidic bond links the anomeric carbons of both glucose and fructose, so neither has a free aldehyde or ketone group to reduce Tollens' or Fehling's reagent.
What is invert sugar?
The equimolar mixture of glucose and fructose formed on hydrolysis of sucrose. It is laevorotatory, so the optical rotation changes sign from dextro to laevo, which is why it is called invert sugar.