PYQ Vault

Playbook

Biomolecules

Carbohydrates, amino acids and proteins, vitamins, enzymes and nucleic acids. A recall chapter, with a few counts of peptides and stereocentres.

Questions in the bank
135
q/paper in 2025–26
1.15
Calculation
15%
Notes pages
7

Strand: Structure and recall

When you’ll see it

A sugar, its linkage or whether it reduces Tollens' reagent; an amino acid, its code or class; a peptide to count or read; a level of protein structure; an enzyme, a vitamin or a nucleic-acid base.

How this chapter is tested

It is a recall chapter. Most questions name a sugar, an amino acid, an enzyme or a vitamin and ask for one exact fact about it, often as a match-the-list where one swapped pair costs the mark. Learn the tables as pairs: sugar and linkage, amino acid and code, vitamin and deficiency disease.

The reasoning that remains is short and repeatable: read D or L from the last stereocentre of a Fischer projection, decide whether any anomeric carbon is still free, count peptide bonds (n − 1) and sequences (n! or kⁿ), and count the hydrogen bonds of DNA from one strand (two per A–T, three per G–C). This is where the numeric answers sit.

Carbohydrates, amino acids and proteins carry most of the chapter. NCERT's text is the reference; a few keys rest on facts outside it, such as the named colour tests from the practical manual, so learn those as stated.

The sub-skills

The distinct skills inside the chapter, in the order to learn them.

  • Classes and glucose reactions

    Every monosaccharide reduces Tollens' reagent, fructose included; HI gives n-hexane, bromine water gluconic acid, nitric acid saccharic acid, acetic anhydride a pentaacetate (five OH groups).

  • D/L, rings and anomers

    D or L from the OH on the last stereocentre, not from the sign of rotation; glucose is a pyranose, fructose a furanose; α and β differ at C-1 (anomers), glucose and galactose at C-4 (epimers).

  • Disaccharides and reducing sugars

    Sucrose α1–β2 is non-reducing; maltose α1–4 and lactose β1–4 reduce; invert sugar is laevorotatory because of fructose; amylose is soluble, amylopectin and glycogen branch at C-6, cellulose is β1–4.

  • Amino acids

    Ten essential: V, L, I, R, K, T, M, F, W, H; D aspartic acid, E glutamic acid, N asparagine, Q glutamine; dipolar ions are high-melting and water-soluble; all but glycine are chiral, threonine and isoleucine with two centres.

  • Peptides and protein structure

    n residues hold n − 1 peptide bonds; read from the free NH₂ end; the biuret test needs two peptide bonds; the primary structure is covalent, the rest held by hydrogen bonds, so denaturation keeps the sequence.

  • Enzymes and vitamins

    Invertase, zymase, diastase (starch to maltose), maltase, urease; A, D, E, K and B₁₂ are stored; B₁ beri-beri, B₂ cheilosis, B₆ convulsions, B₁₂ pernicious anaemia, C scurvy, D rickets, K a longer clotting time.

  • Nucleic acids

    DNA: β-D-2-deoxyribose with A, G, C, T; RNA: β-D-ribose with A, G, C, U; the base sits on C-1′, phosphodiester links join C-5′ to C-3′; A–T has two hydrogen bonds, G–C three.

Traps to expect

Distractor shapes this chapter reuses. The Traps page covers the ones that cut across chapters.

  • Sucrose called reducing, maltose not

    Sucrose uses both anomeric carbons, so it is non-reducing. Maltose leaves one C-1 free, so it reduces.

  • D and L read as + and −

    D-glucose is (+) but D-fructose is (−). D or L is structural; the sign comes from a polarimeter.

  • The Asp, Asn, Glu and Gln codes

    Aspartic acid is D, asparagine N, glutamic acid E, glutamine Q. Neither acid gets A, which is alanine.

  • Denaturation said to break peptide bonds

    Heat and pH break hydrogen bonds; the primary sequence survives. Quaternary structure is the packing of subunits, not the fold of one chain.

  • Both DNA strands counted

    Each base of the given strand already stands for one pair. Counting the complementary strand too doubles the hydrogen-bond total.

Learn it before you drill it

This chapter has full teaching notes — foundations, worked examples, self-checks and a mastery check for each page. Read the notes once, then drill page by page below.

Biomolecules notes

Drill every Biomolecules question

135 questions from the bank, across 7 subtopics.

Drill the 135 questions

Drill one subtopic at a time

The 7 subtopics, in teaching order.

Related playbooks

Often paired with this one — the technique or the trap overlaps. Drill these next.