Biomolecules
Class 12 · Chemistry
4 ideas in Class 12 Chemistry, explained in plain words, with games and quizzes to practise.
Carbohydrates: From Glucose to Starch
Part of: Sugars and Proteins
Sugars are sweet polyhydroxy aldehydes or ketones. One unit means monosaccharide, a few mean oligosaccharide, and hundreds mean polysaccharide. Glucose proves its straight six-carbon aldehyde build through classic reactions, then curls into a ring with a twin form. Sucrose locks two units into a non-reducing pair, while starch, cellulose and glycogen store or build with glucose chains.
Why it matters. Sugars fuel the body and build plants, and structure-proof questions train scientific detective work.
Formulas
- Sucrose plus water gives one glucose plus one fructose
- Sucrose locks C1 of glucose to C2 of fructose, so it cannot reduce
- Starch stores glucose in plants; glycogen stores it in animals
Key words
- Monosaccharide
- : A single sugar unit that cannot be split smaller by hydrolysis.
- Disaccharide
- : Two sugar units joined by a glycosidic link.
- Reducing sugar
- : A sugar with a free aldehyde or ketone end that reduces metal reagents.
- Glycosidic linkage
- : An oxygen bridge between two sugar units formed by losing water.
- Anomer
- : A ring form of a sugar differing only at the first carbon.
- Invert sugar
- : The left-rotating glucose plus fructose mixture from sucrose hydrolysis.
Try it in two minutes
- Sort glucose, sucrose, maltose and starch cards into mono, di and poly piles.
- Ask which piles can reduce Fehling solution and why.
- Link glucose units with paper clips into straight and branched chains.
Try at home. Explain why honey gives instant energy but wood, though full of glucose units, cannot be digested.
Amino Acids and Proteins
Part of: Sugars and Proteins
Proteins are chains of alpha amino acids, each carrying an amino and an acid group on one carbon. In water they wear both charges as a zwitter ion, which explains high melting and solubility. Carboxyl of one plus amino of the next minus water makes a peptide link. Chains fold into helices and sheets, then into fibrous or globular balls; heat or acid scrambles the folds but keeps the sequence.
Why it matters. Proteins build and run the body, and structure levels plus denaturation recur in every exam.
Formulas
- Peptide bond: COOH of one amino acid joins NH2 of the next, minus water
- Denaturation breaks secondary and tertiary shapes; primary stays
- Fibrous proteins are insoluble; globular proteins dissolve
Key words
- Zwitter ion
- : A molecule carrying both a positive and a negative charge, neutral overall.
- Peptide bond
- : An amide link between the acid end of one amino acid and the amino end of the next.
- Essential amino acid
- : An amino acid the body cannot make, so diet must supply it.
- Denaturation
- : Loss of folds and activity while the amino acid sequence stays intact.
- Fibrous protein
- : A parallel-chain protein, usually strong and water-insoluble.
- Globular protein
- : A coiled ball-like protein, usually water-soluble.
Try it in two minutes
- Bead two colours for amino and acid ends and string them alternately.
- Remove a water slip between neighbours to show the peptide link.
- Coil the string, then tangle it to show helix versus ball.
Try at home. Explain why boiled egg white stays solid using folds versus sequence.
Enzymes and Vitamins
Part of: Helpers and Messengers
Enzymes are mostly globular proteins that catalyse body reactions in tiny doses by lowering activation energy. Each fits one substrate, and names often end in ase. Vitamins are tiny diet helpers: A, D, E and K dissolve in fat and store in liver, while B group and C dissolve in water and wash out daily. Shortage of each paints a signature disease.
Why it matters. Enzyme logic explains digestion and energy, and vitamin matching is pure scoring material.
Formulas
- Enzymes lower activation energy; sucrase cuts 6.22 to 2.15 kJ per mol
- Vitamins A, D, E and K dissolve in fat; B group and C dissolve in water
- Water-soluble vitamins leave in urine, except B12
Key words
- Activation energy
- : The energy hump reactants must cross before turning into products.
- Biocatalyst
- : A living-system catalyst, usually an enzyme, that speeds a reaction.
- Fat-soluble vitamin
- : A vitamin stored in liver and fat tissue, such as A, D, E or K.
- Water-soluble vitamin
- : A vitamin that washes out in urine and needs regular supply, like B or C.
- Scurvy
- : Bleeding-gum disease from missing vitamin C.
- Rickets
- : Bone deformity in children from missing vitamin D.
Try it in two minutes
- Act out a lock and key with hands for enzyme and substrate.
- Sort vitamin cards into fat-storing and daily-need piles.
- Match three deficiency cards to their missing vitamins.
Try at home. Check a home kitchen for vitamin C, D and A sources and name one each.
Nucleic Acids and Hormones
Part of: Helpers and Messengers
Nucleic acids chain nucleotides, each a base plus sugar plus phosphate. DNA uses deoxyribose with A, T, G and C in two complementary strands, while RNA uses ribose with U instead of T in one strand that sometimes folds. Hormones are distant messengers: insulin lowers sugar level while glucagon raises it, iodine builds thyroxine, and steroids steer growth and salt balance.
Why it matters. Heredity, protein building and body balance all hang on these two messenger systems.
Formulas
- Nucleoside plus phosphate at the 5 spot gives a nucleotide
- Adenine pairs thymine; cytosine pairs guanine
- Insulin lowers glucose level; glucagon raises it
Key words
- Nucleoside
- : A base joined to a sugar without any phosphate group.
- Nucleotide
- : A nucleoside carrying a phosphate group on the sugar.
- Complementary pairing
- : Strict A with T and C with G matching across DNA strands.
- DNA fingerprinting
- : Identifying a person by their unique DNA base sequence.
- Insulin
- : A protein hormone that lowers glucose levels in the body.
- Thyroxine
- : An iodine-built hormone that sets growth and metabolism pace.
Try it in two minutes
- Pair letter cards A with T and C with G to build a ladder.
- Swap T for U and drop a rail to turn DNA into RNA.
- Act out insulin and glucagon pulling sugar levels opposite ways.
Try at home. Write the complementary DNA strand for ATGCGT and name each pair.
What your child will practise
- Amino Acids and Proteins: Candy Quick Fire (Quick Fire)
- Carbohydrates: From Glucose to Starch: Desert Puzzle (Clue Puzzle)
- Carbohydrates: From Glucose to Starch: Desert Quick Fire (Quick Fire)
- Enzymes and Vitamins: Space Quick Fire (Quick Fire)
- Nucleic Acids and Hormones: Ocean Puzzle (Clue Puzzle)
- Quiz: Amino Acids and Proteins (8 questions)
- Quiz: Carbohydrates: From Glucose to Starch (8 questions)
- Quiz: Enzymes and Vitamins (8 questions)
- Quiz: Nucleic Acids and Hormones (8 questions)