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What happens to an enzyme when it is denatured?
Its tertiary structure (3D shape) changes, particularly the active site, so it can no longer bind substrate effectively The enzyme has died because enzymes are alive
Its tertiary structure (3D shape) changes, particularly the active site, so it can no longer bind substrate effectively.
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Key concepts Triglyceride Glycerol + 3 fatty acids joined by ester bonds
Ester bond Bond between -OH (glycerol) and -COOH (fatty acid), releasing water
Phospholipid Glycerol + 2 fatty acids + phosphate group — forms bilayers
Peptide bond Bond between amino group and carboxyl group of two amino acids
R group Variable side chain that defines each amino acid's properties
Quaternary structure Multiple polypeptide chains joined into a functional protein (e.g. haemoglobin)
Active site Region of enzyme where substrate binds — shape is complementary
Induced fit Active site flexes around substrate, straining its bonds
Km Substrate concentration at ½ Vmax — low Km = high affinity
Vmax Maximum reaction rate when enzyme is saturated with substrate
Competitive inhibitor Similar to substrate — blocks active site, raises Km
Non-competitive inhibitor Binds allosteric site, changes enzyme shape — lowers Vmax
Monomer Small repeating unit (e.g. glucose, amino acid, nucleotide)
Polymer Long chain of monomers joined by condensation
Show all 14 key concepts What your exam board covers Where Biological Molecules sits in each exam board's specification. Tap a board to see what it lists.
AQA Biological molecules Spec 7402 Monomers and polymers Carbohydrates Lipids Proteins Nucleic acids: DNA and RNA ATP Water Inorganic ions Source: AQA A-level Biology (7402) specification — Subject content , accessed 23 June 2026.
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Common mistakes to avoid Questions where students often pick the tempting wrong answer — make sure you know the right one:
What happens to an enzyme when it is denatured? ✗ The enzyme has died because enzymes are alive. ✓ Its tertiary structure (3D shape) changes, particularly the active site, so it can no longer bind substrate effectively.
Why are enzymes specific to certain substrates? ✗ Each enzyme can react with any substrate, but works fastest with one type. ✓ Only substrates with complementary shape and chemistry to the active site can bind effectively.
How does a competitive inhibitor affect enzyme kinetics? ✗ Lowers Vmax, Km unchanged ✓ Raises Km, Vmax unchanged
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