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3.1.43 · Enzymes

Measuring Enzyme Activity — Cambridge AS & A Level Biology 9700 Revision Notes & Topical Questions

5 min read 7 parts Lesson 6 of 17 1 quiz

📚 Cambridge AS & A Level Biology 9700 Hub / Topical Revision
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Lesson summary

3.1.4 Measuring Enzyme Activity — CAMBRIDGE AS & A LEVEL BIOLOGY 9700 — REVISION NOTES notes: Describe investigations of catalase and amylase activity and the variables to control.Product formation — measure how fast a product appears, as with catalase.Substrate disappearance — m…

  • Keep constant
  • Initial rate
  • Hypothesis
  • Colorimeter
  • Transmission
  • Absorbance

Part 1 of 5Two ways to follow a reaction

Product formation
  • Product formation measure how fast a product appears, as with catalase.
Substrate disappearance
  • Substrate disappearance measure how fast a substrate is used, as with amylase.

Part 2 of 5Catalase investigation

1
Hydrogen peroxide is a toxic by-product of metabolism, so catalase breaks it down to water and oxygen.
2
Combine hydrogen peroxide and catalase.
3
Measure the volume of oxygen produced in a set time.
4
Calculate the rate of reaction.

Part 3 of 5Amylase investigation

1
Amylase hydrolyses starch into maltose and glucose, working best at pH 7 and 37 °C.
2
Mix amylase and starch.
3
Take samples at regular intervals and add each to iodine solution.
4
A blue-black colour shows starch is still present; the time taken for it to disappear is measured.
5
Repeat under different conditions such as pH or temperature and compare rates.

Part 4 of 5Control variables

Keep constant
  • Keep constant temperature, pH, enzyme concentration and substrate concentration, except the factor being tested.
Reason
  • Reason otherwise a change in rate cannot be linked to the factor tested.
Initial rate
  • Initial rate compare initial rates by drawing a tangent at t = 0.

Part 5 of 5More from the specification

More from the specification
Catalytic substrate turnover function
  • Catalytic substrate turnover function colorimetric assays monitor product accumulation over time, directly assessing active enzyme catalytic function.
Enzyme Catalytic Action and Activation Energy
  • Enzymes are globular proteins acting as biological catalysts that accelerate biochemical reactions by lowering the activation energy barrier without being consumed in the process.
Induced-Fit Hypothesis and Enzyme-Substrate Complex
  • The induced-fit hypothesis proposes that the enzyme active site adjusts its shape slightly upon contact with the specific substrate,
  • forming an enzyme-substrate complex that strains substrate bonds.
Colorimetric Measurement of Reaction Rates
  • A colorimeter measures changes in light absorbance or transmission over time as colored reactants or products change, calibrated with a blank solution to ensure accurate transmission baselines.
Active Site Saturation and Vmax
  • At high substrate concentrations, all enzyme active sites become saturated with substrate molecules,
  • causing the initial reaction rate to reach maximum velocity (Vmax) where enzyme concentration is limiting.
Activation energy
  • The energy needed for a substrate to become unstable enough to react.
Enzyme-substrate complex
  • The temporary structure formed when a substrate binds to an enzyme's active site.
Induced-fit hypothesis
  • The active site changes shape to fit the substrate.
Lock-and-key hypothesis
  • Rigid enzyme and substrate fit exactly.
Globular protein
  • A rounded, usually soluble protein, such as an enzyme or insulin.
Extracellular enzyme
  • An enzyme secreted to work outside cells.
Specific
  • Able to act on only one type of substrate.
Complex
  • Two or more molecules joined, such as an antibody and antigen.
Hypothesis
  • A testable prediction with a scientific explanation.
Colorimeter
  • An instrument that measures light absorbed by a solution.
Transmission
  • The amount of light passing through a sample.
Protein
  • A long chain of amino acids containing carbon, hydrogen, oxygen and nitrogen.
Absorbance
  • A measure of the light absorbed by a sample.

Key terms

TermMeaning
CatalaseAn enzyme that breaks hydrogen peroxide into water and oxygen.
AmylaseAn enzyme that hydrolyses starch to maltose.
Rate of reactionThe amount of product formed or substrate used per unit time.
Control variableA variable kept constant in an investigation.
Hydrogen peroxideA toxic by-product of metabolism.
Iodine solutionA reagent that turns blue-black with starch.

Avoid these mistakes

1
Failing to control variables — changes in rate then cannot be attributed to the tested factor.
2
Using one sample only — repeat each condition and calculate a mean.
3
Reading the iodine test at one time only — sample at regular intervals.
4
Saying catalase makes oxygen from water — it breaks hydrogen peroxide into water and oxygen.

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