Is it correct to say: Confusing peptide bond with glycosidic bond?

Peptide bond joins amino acids (−CO−NH−); glycosidic bond joins sugars (C−O−C).

Is it correct to say: Assuming DNA has uracil?

DNA has T (thymine); RNA has U (uracil). Interchanging them is a common error.

Is it correct to say: Writing α and β glucose as constitutional isomers?

They are anomers — stereoisomers differing at the anomeric C-1 only.

Is it correct to say: Confusing denaturation with degradation?

Denaturation: loss of 2°, 3°, 4° structure but not peptide bonds. Degradation breaks peptide bonds.

Is it correct to say: Using −COOH and −NH₂ as separate groups in isoelectric calculation?

At pI both are ionised — you must consider the zwitterion. pI = ½(pK₁ + pK₂) for neutral amino acid.

Is it correct to say: Assuming vitamins provide energy?

Vitamins are co-factors for enzymes; they do not directly provide energy.

Formula sheet (PDF) →

Chemistry · Chapter 14

Biomolecules

Carbohydrates, proteins, enzymes, vitamins, nucleic acids, hormones — Maharashtra HSC Chemistry Ch 14

10 formulas · 3 solved examples · 5 practice questions · Board weight: 4 marks · Maharashtra State Board Class 12 · 2025–26 syllabus

Board Exam Tips

→Distinguish clearly between α- and β-glucose Haworth projections — the C-1 OH orientation is often asked as a 2-mark diagram.
→Reactions of glucose (with HCN, HI/red P, Br₂ water, Fehling's, Tollens') and structure elucidation from these are a 3-mark HSC classic.
→Peptide bond formation and structure of proteins (primary, secondary, tertiary, quaternary) is a 3-marker every year.
→For nucleic acids, learn the base pairing (A=T, G≡C) — asked in short answer questions.
→Denaturation of proteins vs coagulation of proteins — Maharashtra Board often asks the difference.

Formulas(10)

Peptide BondBoard favourite

α -amino acid H_{2} N - C H R - C O O H + H_{2} N - C H R^{'} - C O O H \to H_{2} N - C H R - C O - N H - C H R^{'} - C O O H + H_{2} O

Zwitterion Form of Amino Acid

H_{3} N + - C H R - C O O^{-}

Isoelectric Point (pI)

p I = \frac{1}{2} (p K_{a 1} + p K_{a 2})

Glycosidic BondBoard favourite

Two sugars + glycosidic bond \to disaccharide + H_{2} O

Fischer to Haworth Conversion — Cyclisation

aldose or ketose ⇌ cyclic hemiacetal/hemiketal

Base Pairing in DNABoard favourite

A = T (2 H-bonds), G \equiv C (3 H-bonds)

DNA vs RNA — Sugar

DNA: 2-deoxyribose; RNA: ribose

Enzyme Rate — Michaelis-Menten (simplified)

v = \frac{V _{ma x} [ S ]}{K _{m} + [ S ]}

Optical Activity of GlucoseBoard favourite

[α]_{D}^{25 ° C} = + 52.7° (equilibrium)

Iodine Test for Starch

Starch + I_{2} \to Deep blue colour

Solved Examples

1Solved Exampleeasy4 steps

Draw the structures of α-D-glucose and β-D-glucose (Haworth projections) and identify the anomeric carbon.

Glucose forms 6-membered pyranose ring. C-1 becomes chiral (anomeric).

Anomeric C = C-1

2Solved Exampleboard4 steps

Explain briefly the primary, secondary, tertiary and quaternary structures of proteins.

Primary structure: linear sequence of amino acids joined by peptide bonds.

aa_{1} - aa_{2} - aa_{3} - \dots

3Solved ExampleHOTS4 steps

Glucose forms an oxime with hydroxylamine, but pentaacetate of glucose does not. Explain.

Oxime formation requires free carbonyl (−CHO in glucose).

R - C H O + N H_{2} O H \to R - C H = N - O H + H_{2} O

Traps & Common Mistakes

Common Mistakes6

1
Confusing peptide bond with glycosidic bond
✓Peptide bond joins amino acids (−CO−NH−); glycosidic bond joins sugars (C−O−C).
2
Assuming DNA has uracil
✓DNA has T (thymine); RNA has U (uracil). Interchanging them is a common error.
3
Writing α and β glucose as constitutional isomers
✓They are anomers — stereoisomers differing at the anomeric C-1 only.
4
Confusing denaturation with degradation
✓Denaturation: loss of 2°, 3°, 4° structure but not peptide bonds. Degradation breaks peptide bonds.
5
Using −COOH and −NH₂ as separate groups in isoelectric calculation
✓At pI both are ionised — you must consider the zwitterion. pI = ½(pK₁ + pK₂) for neutral amino acid.
6
Assuming vitamins provide energy
✓Vitamins are co-factors for enzymes; they do not directly provide energy.

Practice Yourself

Practice Yourself5 questions

Q1
Name the disease caused by deficiency of vitamin C.
Q2
Distinguish between DNA and RNA in three points.
Q3
Give one example of a fibrous protein and one of a globular protein.
Q4
Give the products of hydrolysis of sucrose.
Q5
Which vitamins are water-soluble?

Notes

Biomolecules — Maharashtra HSC Overview

Chapter 14 of the Balbharati Class 12 Chemistry textbook covers carbohydrates, proteins, amino acids, enzymes, vitamins, nucleic acids and hormones.

Maharashtra syllabus specifics

Structure elucidation of glucose from reactions (open chain vs cyclic; anomeric C-1) is explicitly asked as a 3-marker.
Denaturation vs coagulation of proteins — 2-mark distinction. Balbharati insists on the difference.
Enzyme catalysis — lock-and-key model, induced-fit model, and factors affecting enzyme activity — is asked as 2-marker with diagram.
Watson–Crick DNA double-helix structure with base pairing (A=T, G≡C) — 3-mark question.
Vitamin deficiency diseases — a Maharashtra staple 1-mark objective (e.g. rickets, beri-beri, scurvy, pellagra, night blindness).
Some editions of Balbharati also cover hormones briefly — steroid, peptide, amine — as a 2-marker.

Study tips

Learn Haworth projections for α and β glucose; the CHIRAL center at C-1 is key.
Draw peptide bond formation with proper arrow pushing.
Memorise vitamin sources, chemical names, deficiency diseases, and water/fat solubility.
For DNA/RNA questions, remember Chargaff's rule and the sugar-phosphate backbone.