MHT-CET Chemistry · Biomolecules

Lipids, Enzymes and Other Biomolecules

Fats and oils are triglycerides — triesters of glycerol with three fatty acids, hydrolysed by three water molecules and saponified to soap, the sodium or potassium salt of a higher fatty acid; the common fatty acids are counted by carbons and double bonds (linolenic 18:3), enzymes are globular protein catalysts named for their substrate and site, and haemoglobin is the biological coordination compound.

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Why this matters

16 PYQs, none HARD — a short page, though 2026 alone added eleven. Of the five set from 2021 to 2025, two ask the number of C=C bonds in linolenic acid (three), one the water needed to hydrolyse n mol of triglyceride (3n), one what a soap is (K or Na salt of a higher fatty acid), one the enzymes in saliva; haemoglobin as a coordination compound sits here too. One card.

Concept 1 of 1: Triglycerides, Fatty Acids, Soap and Enzymes

A triglyceride has three ester bonds, so complete hydrolysis needs three waters per molecule and returns glycerol plus three fatty acids; done with NaOH or KOH it gives the salts instead — soap. A fatty acid is described by two numbers, carbons and C=C: palmitic 16:0 and stearic 18:0 are saturated (solid fats), oleic 18:1, linoleic 18:2 and linolenic 18:3 are unsaturated (oils). Enzymes are proteins that speed one reaction each; the name usually says what they act on (amylase on starch, lipase on fats, pepsin and trypsin on proteins).

Definition

Triglyceride = glycerol + 3 fatty acids (3 ester links). Hydrolysis: $n$ mol triglyceride needs $3n$ mol $\text{H}_2\text{O}$ → glycerol + 3 RCOOH.
Soap = sodium or potassium salt of a higher fatty acid (C12–C18); Na gives hard soap, K soft soap. Formic-acid or ammonium salts are not soaps.
Fatty acids: palmitic $\text{C}_{15}\text{H}_{31}\text{COOH}$ (16:0), stearic $\text{C}_{17}\text{H}_{35}\text{COOH}$ (18:0), oleic 18:1, linoleic 18:2, linolenic 18:3 (9,12,15-octadecatrienoic acid — three C=C).
Enzymes: globular proteins, highly specific, work at body temperature and pH. Saliva: amylase (ptyalin), lysozyme, lingual lipase; stomach: pepsin (with HCl); intestine: trypsin, lactase; invertase hydrolyses sucrose.
Haemoglobin: Fe(II) held by the porphyrin ring — a coordination compound in blood; chlorophyll (Mg) is the plant counterpart, and vitamin B12 holds cobalt.

Triglyceride hydrolysis

\text{triglyceride} + 3\,\text{H}_2\text{O} \to \text{glycerol} + 3\,\text{RCOOH};\qquad \text{linolenic acid: } \text{C}_{18},\ 3\ \text{C=C}

Worked example

How many moles of NaOH saponify 2 mol of a triglyceride completely, and what are the products?

Practise this conceptself-check · 4 quick reps

The same idea in a real exam question:

MHT-CET · 2025 · 19 April Shift II · Q72Moderate

Example 1 · Biomolecules · Lipids, Enzymes and Other Biomolecules

What is the number of

> C = C <

bonds present in a linolenic acid molecule?

Linoleic for linolenic

One letter apart: linoleic acid has TWO C=C, linolenic THREE. The '-trien-' in 9,12,15-octadecatrienoic acid gives the count.

Drill 3 more on triglycerides, fatty acids, soap and enzymes

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.

Formulas (1)

Triglycerides, Fatty Acids, Soap and Enzymes
Triglyceride hydrolysis
$\text{triglyceride} + 3\,\text{H}_2\text{O} \to \text{glycerol} + 3\,\text{RCOOH};\qquad \text{linolenic acid: } \text{C}_{18},\ 3\ \text{C=C}$

Watch out for (1)

Linoleic for linolenic
→ Triglycerides, Fatty Acids, Soap and Enzymes

Test yourself on Biomolecules

20 past MHT-CET questions from this chapter, timed at 18 minutes and marked the way the exam marks it. You see your score and every answer the moment you finish. Free to start.

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