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C1.1.7—Relationships between structure and function

Enzyme function depends on active-site structure, chemical attraction and tertiary shape that allow only suitable substrates to bind effectively during catalysis.

Syllabus
First assessment 2025
Objective
C1.1.7
Level
SL

Exam analysis

Chance of appearing1%of analysed past papers
Latest appearanceMay 2018
Most common paperPaper2
Typical marks3–6

Common command terms

  • Explain

Recent exam appearances

May 2018Paper2 ["SL"] · TZ24(b)[ 3 ]C1.1.7—Relationships between structure and function
November 2013Paper2 ["SL"] · TZ07(b)[ 6 ]C1.1.7—Relationships between structure and function
Practice this objective

Coverage 2013–2018 · Updated 15 Jul 2026

Small Structural Changes Can Alter Enzyme Function

Enzyme function depends on the relationship between amino-acid sequence, three-dimensional shape and active-site chemistry.

A mutation, pH shift or temperature change can alter bonds maintaining the fold. If substrate contacts or catalytic residues move, binding and reaction rate change even when the protein is still present.

Trace a structure–function effect:

  • structural change
  • active-site geometry
  • substrate binding
  • rate or specificity

Replacing a charged residue in an active site with a non-polar one can remove an ionic interaction and lower catalytic activity.

A smaller enzyme band or unchanged concentration does not prove that its active site still works.

Relationships between structure and function

Assessment in practice

2–6 marks
How it is assessed

This objective is assessed through structured response, commonly using Explain.

Command terms

Explain

What earns marks

Build the answer around this relationship: Active-site structure determines which substrates can bind.

Representative question

Question 1

[Maximum number: 6]

Some proteins in membranes act as enzymes. Outline enzyme-substrate specificity.

Enzyme Catalysis and Rate

Enzymes are biological catalysts that lower activation energy and remain unchanged. Their globular protein shape creates active-site specificity; induced fit aligns substrates; molecular motion and collisions affect rate; temperature, pH, and substrate concentration change activity; assays measure substrate loss or product formation over time.

  • Define enzyme as biological catalyst, effective in small amounts and unchanged.
  • Use active site, specificity, induced fit, ES complex, and activation energy in mechanism answers.
  • Use curve shapes: temperature optimum/denaturation, pH optimum, and substrate saturation plateau.
  • For practicals, state what is measured per unit time and use initial rate, controls, and replicates.

Concept essentials

  • Active-site structure determines which substrates can bind.
  • Specificity depends on shape and chemical properties.
  • Denaturation changes tertiary structure and active-site function.
  • Enzyme-substrate complex formation depends on structural compatibility.
ConceptIB Biology SL