Biological molecules and enzymes: every key term you need (+ practice quiz)
16 flashcard terms for A-Level Biology Topic 1, written to match the course framework. Study them here, then drill them as interactive flashcards, or test yourself with the 8-question quiz — free, no account needed.
Joins two monomers and releases one molecule of water. Builds every biological polymer — polysaccharides, polypeptides and polynucleotides.
Hydrolysis
Splits a bond between two monomers using a molecule of water. The reverse of condensation, and how digestion breaks polymers down.
Glycosidic bond
The covalent bond linking two monosaccharides, formed by condensation. 1,4 links give straight chains; 1,6 links create branches.
Starch vs glycogen
Both are glucose stores. Starch (plants) is amylose plus amylopectin; glycogen (animals) is more highly branched, so it is hydrolysed faster.
Cellulose
Beta-glucose polymer with alternate molecules inverted. Straight chains hydrogen-bond into microfibrils, giving plant cell walls tensile strength.
Triglyceride
One glycerol plus three fatty acids joined by ester bonds. Energy-dense and hydrophobic, so it stores energy without osmotic effect.
Phospholipid bilayer
Hydrophilic phosphate heads face the water, hydrophobic tails face inwards. This self-assembly is why membranes form spontaneously.
Peptide bond
Formed by condensation between the amine group of one amino acid and the carboxyl group of the next, releasing water.
Tertiary structure
The overall 3D fold of a polypeptide, held by hydrogen bonds, ionic bonds, disulfide bridges and hydrophobic interactions.
Induced fit model
The active site is not rigid — it changes shape slightly as the substrate binds, straining bonds and lowering activation energy.
Activation energy
The energy needed to start a reaction. Enzymes lower it, so reactions proceed far faster at body temperature.
Competitive inhibitor
Similar shape to the substrate; binds the active site. Its effect is reduced by raising substrate concentration.
Non-competitive inhibitor
Binds away from the active site and alters its shape. Raising substrate concentration does not overcome it.
Denaturation
Loss of tertiary structure when bonds break above the optimum temperature or away from optimum pH. The active site no longer complements the substrate.
Biuret test
Tests for protein. Add sodium hydroxide then copper(II) sulfate — a purple colour indicates peptide bonds are present.
Benedict's test
Tests for reducing sugar. Heat with Benedict's solution: blue to green to brick-red as concentration increases.