"What are the monomers of proteins" is searched about 2,700 times a month in the United States, and the same question for carbohydrates, nucleic acids and lipids follows it, because the four macromolecules open every high-school and AP Biology course (Unit 1) and the "monomer, bond, polymer" table is the first thing examined. This page gives the chart in full, the two reactions that build and break every macromolecule, the functions, the food tests, the trap questions (lipids are not polymers; ATP is a nucleotide), the curriculum placements and a printable chart with practice.
Download the macromolecules chart with practice (PDF) (A4, the chart, the reactions and the functions on page 1, the detail tables, the tests and the practice set with answers on page 2, free).
The chart
| Macromolecule | Monomer (building block) | Bond between monomers | Polymer (examples) | Elements | Main functions |
|---|---|---|---|---|---|
| Carbohydrates | monosaccharides: glucose, fructose, galactose (C₆H₁₂O₆); ribose, deoxyribose | glycosidic bond | disaccharides (sucrose, lactose, maltose); polysaccharides (starch, glycogen, cellulose, chitin) | C, H, O (in the ratio 1 : 2 : 1) | quick energy (glucose), energy storage (starch in plants, glycogen in animals), structure (cellulose in plant cell walls, chitin in fungi and insects) |
| Proteins | amino acids (20 kinds) | peptide bond | polypeptides, folded into proteins (enzymes, haemoglobin, collagen, keratin, antibodies, insulin) | C, H, O, N (some S) | enzymes, structure, transport, signalling, defence, movement (actin, myosin) |
| Nucleic acids | nucleotides (sugar + phosphate + base: A, T or U, G, C) | phosphodiester bond | DNA (deoxyribose, double helix), RNA (ribose, single strand) | C, H, O, N, P | store and transmit genetic information; RNA carries it to ribosomes; ATP (a nucleotide) carries energy |
| Lipids | not a polymer: fatty acids + glycerol (triglycerides, phospholipids); four fused rings (steroids) | ester bond (fatty acid to glycerol) | triglycerides (fats, oils), phospholipids, steroids (cholesterol, hormones), waxes | C, H, O (very little O); P in phospholipids | long-term energy storage, cell membranes (phospholipid bilayer), insulation, waterproofing, hormones |
The memory hook: proteins, peptide; carbs, glycosidic; nucleic, phosphodiester; lipids, ester (and not a polymer).
The two reactions that build and break everything
Dehydration synthesis (condensation): two monomers join and a molecule of water is removed (an OH from one, an H from the other). glucose + glucose → maltose + H₂O. amino acid + amino acid → dipeptide + H₂O. Every polymer in the chart is built this way, one monomer at a time, by enzymes.
Hydrolysis: a polymer is split and a molecule of water is added across the bond. maltose + H₂O → glucose + glucose. This is digestion: amylase hydrolyses starch to maltose, proteases hydrolyse proteins to amino acids, lipases hydrolyse triglycerides to fatty acids and glycerol. The products are small enough to be absorbed, then rebuilt by dehydration synthesis into the body's own polymers.
The names are the exam's: hydro water, lysis splitting; dehydration removing water.
Carbohydrates in more detail
| Level | Examples | Notes |
|---|---|---|
| Monosaccharides | glucose, fructose (fruit sugar), galactose; ribose and deoxyribose (5 carbons) | glucose, fructose and galactose are isomers: same formula C₆H₁₂O₆, different arrangement |
| Disaccharides | sucrose = glucose + fructose (table sugar); lactose = glucose + galactose (milk); maltose = glucose + glucose (malt) | one glycosidic bond each |
| Polysaccharides | starch (amylose and amylopectin; plant energy store), glycogen (animal energy store, in liver and muscle, highly branched), cellulose (plant cell walls; straight chains hydrogen-bonded into fibres; humans cannot digest it: fibre), chitin (fungal cell walls, insect exoskeletons) | all made of glucose; the bond orientation (alpha in starch and glycogen, beta in cellulose) decides digestibility |
Proteins in more detail
Each amino acid has a central carbon with an amino group (–NH₂), a carboxyl group (–COOH), a hydrogen and an R group (side chain) that makes it one of the 20 kinds: polar, non-polar, acidic, basic. The peptide bond forms between the carboxyl of one and the amino of the next, releasing water. The chain folds into four levels of structure: primary (the sequence of amino acids), secondary (alpha helices and beta pleated sheets held by hydrogen bonds), tertiary (the overall 3D fold, held by R-group interactions: hydrogen bonds, ionic bonds, disulfide bridges, hydrophobic interactions) and quaternary (several polypeptides together, as in haemoglobin's four chains). Shape is function: heat or pH change unfolds the protein (denaturation) and it stops working, which is why fevers are dangerous and eggs set.
Nine of the 20 amino acids are essential in the human diet (the body cannot make them).
Nucleic acids in more detail
A nucleotide is a pentose sugar (deoxyribose in DNA, ribose in RNA), a phosphate group and a nitrogenous base: adenine (A), guanine (G), cytosine (C) and thymine (T) in DNA or uracil (U) in RNA. The phosphodiester bond links the phosphate of one nucleotide to the sugar of the next, making the sugar-phosphate backbone; the bases hang off it and pair across the two strands of DNA (A with T, G with C) by hydrogen bonds. DNA is a double helix; RNA is single-stranded (mRNA, tRNA, rRNA). ATP (adenosine triphosphate) is a nucleotide with three phosphates, the cell's energy currency, which is why "ATP is a nucleic acid monomer" is a true statement that surprises students.
Lipids in more detail
Lipids are the macromolecules that are not polymers: they are not chains of repeating monomers but assemblies of a few parts, held together because they are all hydrophobic.
- Triglycerides (fats and oils): one glycerol and three fatty acids joined by ester bonds (dehydration synthesis again, three waters out). Saturated fatty acids have no C=C double bonds, pack tightly and are solid at room temperature (butter, lard); unsaturated have double bonds that kink the chain, so they are liquid (olive oil). Twice the energy per gram of carbohydrate.
- Phospholipids: glycerol, two fatty acids and a phosphate group. The phosphate head is hydrophilic and the tails hydrophobic, so in water they form the bilayer of every cell membrane.
- Steroids: four fused carbon rings; cholesterol (in membranes), testosterone, oestrogen, cortisol.
- Waxes: long fatty acids and alcohols; waterproofing on leaves and feathers.
The food tests
| Test | For | Reagent | Positive result |
|---|---|---|---|
| Benedict's test | reducing sugars (glucose, maltose) | Benedict's solution, heated | blue → green → yellow → brick red |
| Iodine test | starch | iodine solution | yellow-brown → blue-black |
| Biuret test | proteins | sodium hydroxide then copper sulfate (biuret reagent) | blue → purple (lilac) |
| Emulsion (ethanol) test | lipids | ethanol, then water | clear → cloudy white emulsion |
The trap questions
- "What is the monomer of lipids?" None; lipids are not polymers. Write fatty acids and glycerol if forced.
- "Starch, glycogen and cellulose are all made of what?" Glucose. The difference is the bond and the branching.
- "Is ATP a nucleic acid?" It is a nucleotide, the monomer, not a nucleic acid.
- "Which macromolecule contains nitrogen?" Proteins and nucleic acids (both); carbohydrates and most lipids do not. Phosphorus: nucleic acids and phospholipids.
- "What type of reaction builds a polymer?" Dehydration synthesis (condensation), not hydrolysis.
- "Are enzymes carbohydrates?" No: enzymes are proteins.
Where it sits in each curriculum
| Curriculum | When | What is expected |
|---|---|---|
| US | high-school biology (HS-LS1-6: carbon-based molecules), AP Biology Unit 1, Chemistry of Life (the four macromolecules, monomers, dehydration and hydrolysis, structure and function) | the chart in full, the two reactions, protein structure |
| England | GCSE Biology (digestion: carbohydrates, proteins and lipids and their building blocks; the food tests required practical), A-level Biology (biological molecules: monosaccharides to polysaccharides, amino acids and protein structure, lipids, nucleotides and DNA) | GCSE: building blocks, enzymes, tests; A-level: bonds and structures |
| Australia | Year 11 Biology (cells and multicellular organisms: biomacromolecules), Year 12 (DNA, proteins) | the four groups and their roles |
| India (CBSE) | Class 11 (Biomolecules: primary and secondary metabolites, amino acids, lipids, nucleotides, polysaccharides, protein structure), Class 12 (Molecular Basis of Inheritance) | the chapter in full |
| IB Biology | Topics B1.1 (carbohydrates and lipids) and B1.2 (proteins), A1.2 (nucleic acids) | monomers, condensation and hydrolysis, structure |
Practice (answers in the PDF)
- Complete the row for each macromolecule: monomer, bond, one example polymer, one function.
- Write a word equation for two glucose molecules joining, and name the reaction and the bond.
- Why are lipids not classed as polymers?
- A food sample turns blue-black with iodine and purple with biuret reagent, and gives no colour change with Benedict's solution. What does it contain?
- Name the three parts of a nucleotide and the two differences between a DNA nucleotide and an RNA nucleotide.
- Explain what happens to an enzyme at high temperature and why it stops working.
Download the chart and the practice set (PDF)
Where to get help
A 1-on-1 online biology class with a tutor who teaches AP Biology, GCSE, A-level and IB biology, CBSE Class 11 and 12 and the Australian Years 11 and 12 every week: the macromolecules taught from the chart outward, with the dehydration-hydrolysis pair drawn until it is automatic and the trap questions rehearsed. The biology page lists the courses; the free 30-minute first class is a real lesson on this week's topic. Related pages: the light-dependent reactions of photosynthesis and the 100 common compounds chart.
Questions parents ask
1What are the monomers of proteins?
2What are the monomers of carbohydrates?
3What are the monomers of nucleic acids?
4What is the monomer of lipids?
5How do monomers join to make polymers?
See how we teach this, 1-on-1 online →
Shobha
Founder and lead tutor, Science with Shobha
Teaching maths, science and English to children online since 2018. 500+ students, 20+ tutors, families in nine countries.