Is it correct to say: Saying sucrose is a reducing sugar because glucose is.?

Sucrose has both anomeric carbons locked in the glycosidic bond → NON-reducing. Only free anomeric –OH gives reducing behaviour.

Is it correct to say: Confusing DNA and RNA — writing thymine in RNA.?

DNA has thymine (T); RNA replaces T with URACIL (U). Also DNA uses deoxyribose (no OH at C-2), RNA uses ribose.

Is it correct to say: Treating all polysaccharides as digestible.?

α-1,4 linked (starch, glycogen) are digestible by humans; β-1,4 linked (cellulose) is not — humans lack the β-1,4 glucosidase enzyme.

Is it correct to say: Writing amino acid structure without the zwitterion in the solid state.?

Solid amino acids exist as ionic zwitterions (–NH₃⁺, –COO⁻), giving them high melting points and water solubility.

Is it correct to say: Confusing primary, secondary, tertiary and quaternary protein structure.?

Primary = amino acid sequence; secondary = local folding (α-helix, β-sheet, H-bonds); tertiary = overall 3-D shape; quaternary = assembly of multiple polypeptide subunits.

Is it correct to say: Assuming all vitamins are water-soluble.?

A, D, E, K are FAT-soluble (stored in body, deficiency slow to appear). B-complex and C are WATER-soluble (excreted, need daily intake).

Biomolecules

Carbohydrates, proteins, enzymes, vitamins, nucleic acids and hormones — NCERT Class 12 Chemistry Ch 10

📐 9 formulas✏️ 3 examples🎯 6 practice⚖️ 4-6 marks🏫 CBSE📚 Class 12✓ 2025–26 syllabus

💡

Board Exam Tips

→Classification of carbohydrates (mono-, di-, polysaccharides) and REDUCING vs NON-reducing sugars is a repeated MCQ.
→Peptide bond (–CO–NH–) formation, Zwitterion structure of amino acids, and isoelectric point — high-yield concepts.
→Distinguish α-helix and β-pleated sheet in protein secondary structure — repeats every year in 2-mark form.
→DNA vs RNA differences: sugar (deoxyribose vs ribose), pyrimidine (T vs U), strands (double vs single). Learn table.
→Learn one deficiency disease per vitamin: A → night blindness, B1 → beri-beri, C → scurvy, D → rickets, K → poor clotting.

📐 Formulas(9)

Molecular Formula of Glucose

C_{6} H_{12} O_{6}, M = 180 g/mol; aldohexose

Sucrose Hydrolysis (Inversion of Sugar)★ Board fav

C_{12} H_{22} O_{11} + H_{2} O H^{+} / invertase glucose + fructose

Reducing vs Non-reducing Sugars★ Board fav

Reducing: glucose, fructose, maltose, lactose; Non-reducing: sucrose

Peptide Bond Formation★ Board fav

R_{1} -COOH + H_{2} N-R_{2} - H_{2} O R_{1} -CO-NH-R_{2}

Zwitterion (Amino Acid at Isoelectric Point)

H_{2} N-CHR-COOH ⇌ H_{3} N + -CHR-COO^{-}

Chargaff's Rules (Base Pairing in DNA)★ Board fav

[A] = [T], [G] = [C], [A] + [G] = [T] + [C] = 50%

α-Amino Acid General Structure

H_{2} N-CH(R)-COOH (α -carbon bears -NH_{2}, -COOH, -H, -R)

Michaelis-Menten Equation

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

Symbol	Meaning
$v$	Reaction velocity
$v_{m a x}$	Maximum velocity (at saturating [S])
$[S]$	Substrate concentration
$K_{m}$	Michaelis constant

Glycosidic Linkage Classification

Maltose: α -1,4; Lactose: β -1,4; Sucrose: α -1, β -2; Starch amylose: α -1,4; Cellulose: β -1,4

✏️ Solved Examples

1Solved Exampleeasy3 steps

A DNA sample contains 20% adenine. Using Chargaff's rules, calculate the % of thymine, guanine and cytosine.

Chargaff: [A] = [T]

[T] = [A] = 20%

2Solved Exampleboard4 steps

Explain why sucrose is called a non-reducing sugar while maltose is a reducing sugar, though both are disaccharides.

In sucrose, C-1 (anomeric C) of α-glucose is linked to C-2 (anomeric C) of β-fructose

α -D-glucose-(1 \to 2)- β -D-fructose

3Solved ExampleHOTS4 steps

An amino acid has pKa₁ (–COOH) = 2.34 and pKa₂ (–NH₃⁺) = 9.60. (i) Calculate its isoelectric point. (ii) Predict the direction of migration in an electric field at pH 6.0 and at pH 12.0.

Isoelectric point for a monoamino monocarboxylic acid

pI = \frac{pK _{a 1} + pK _{a 2}}{2} = \frac{2.34 + 9.60}{2}

⚠️ Traps & Common Mistakes

⚠️Common Mistakes6

1
Saying sucrose is a reducing sugar because glucose is.
✓Sucrose has both anomeric carbons locked in the glycosidic bond → NON-reducing. Only free anomeric –OH gives reducing behaviour.
2
Confusing DNA and RNA — writing thymine in RNA.
✓DNA has thymine (T); RNA replaces T with URACIL (U). Also DNA uses deoxyribose (no OH at C-2), RNA uses ribose.
3
Treating all polysaccharides as digestible.
✓α-1,4 linked (starch, glycogen) are digestible by humans; β-1,4 linked (cellulose) is not — humans lack the β-1,4 glucosidase enzyme.
4
Writing amino acid structure without the zwitterion in the solid state.
✓Solid amino acids exist as ionic zwitterions (–NH₃⁺, –COO⁻), giving them high melting points and water solubility.
5
Confusing primary, secondary, tertiary and quaternary protein structure.
✓Primary = amino acid sequence; secondary = local folding (α-helix, β-sheet, H-bonds); tertiary = overall 3-D shape; quaternary = assembly of multiple polypeptide subunits.
6
Assuming all vitamins are water-soluble.
✓A, D, E, K are FAT-soluble (stored in body, deficiency slow to appear). B-complex and C are WATER-soluble (excreted, need daily intake).

🎯 Practice Yourself

🎯Practice Yourself6 questions

Q1
State the difference between an α-helix and a β-pleated sheet.
Q2
Give one example each of a monosaccharide, disaccharide, and polysaccharide.
Q3
The isoelectric point of an amino acid is 5.5. At pH 8, will it move to the anode or the cathode?
Q4
What is the difference between essential and non-essential amino acids? Give one example of each.
Q5
Give two differences between DNA and RNA.
Q6
Name the vitamins whose deficiencies cause: (a) night blindness (b) scurvy (c) rickets (d) beri-beri.

📝 Notes

Biomolecules

Chemistry of the four classes of molecules that make up living cells — carbohydrates, proteins, nucleic acids, and lipids — plus vitamins, hormones and enzymes that regulate biological processes.

Carbohydrates — the energy currency

Polyhydroxy aldehydes / ketones (or compounds that hydrolyse to them). Classified by hydrolysis:

Monosaccharides (glucose, fructose, ribose): cannot be hydrolysed further.
Oligosaccharides (sucrose, maltose, lactose): 2–10 monosaccharide units.
Polysaccharides (starch, glycogen, cellulose): many monomer units in a chain.

Reducing vs non-reducing: a sugar is reducing if it has a free hemiacetal / hemiketal that can regenerate the open-chain –CHO or C=O form. Glucose, fructose, maltose, lactose reduce Tollens' / Fehling's / Benedict's reagents. Sucrose does NOT.

α vs β anomers: in cyclic pyranose form, C-1 –OH can be below (α) or above (β) the ring plane. α-D-glucose ⇌ β-D-glucose interconverts through the open chain — a process called mutarotation.

Proteins — polymers of α-amino acids

Amino acids are joined by peptide (–CO–NH–) bonds. 20 standard α-amino acids in nature; all except glycine are chiral, and all natural ones are of L-configuration. Essential amino acids must come from diet.

Four levels of protein structure:

Primary — amino acid sequence.
Secondary — α-helix or β-pleated sheet held by H-bonds along backbone.
Tertiary — overall 3-D shape (globular, fibrous), stabilised by disulfide bridges, H-bonds, ionic and hydrophobic interactions.
Quaternary — multiple polypeptide chains assembled (e.g. haemoglobin = 4 subunits).

Denaturation = loss of secondary/tertiary structure by heat, pH, urea → protein becomes biologically inactive (boiled egg).

Enzymes — biocatalysts

Enzymes are globular proteins that catalyse specific reactions with lock-and-key or induced-fit binding of substrate. Michaelis–Menten kinetics describes rate vs [S]. Small K_m ⇒ enzyme has HIGH affinity for its substrate.

Vitamins

Organic compounds required in small quantities for normal metabolism. Fat-soluble: A, D, E, K. Water-soluble: B-complex, C.

Nucleic acids — DNA and RNA

DNA (deoxyribonucleic acid): double helix (Watson-Crick, 1953). Deoxyribose sugar, bases A, T, G, C. Stores genetic information.
RNA (ribonucleic acid): single-stranded. Ribose sugar, bases A, U, G, C. Types: mRNA, tRNA, rRNA — carry out protein synthesis.
Nucleotide = base + sugar + phosphate. Bases: purines (A, G, larger) and pyrimidines (C, T, U, smaller). Chargaff's rule enforces base pairing in DNA.