C1.1.5—Induced-fit binding
Induced-fit binding means substrate interaction changes active-site shape, aligning catalytic groups and straining substrate bonds during enzyme action in cells.
- Syllabus
- First assessment 2025
- Objective
- C1.1.5
- Level
- SL
Exam analysis
Chance of appearing4%of analysed past papers
Latest appearanceMay 2025
Most common paperPaper3
Typical marks2–3
Common command terms
- Describe
- Outline
Recent exam appearances
May 2025Paper1A ["SL"] · TZ15[ 1 ]C1.1.5—Induced-fit binding
November 2015Paper3 ["SL"] · TZ08(b)[ 3 ]C1.1.5—Induced-fit binding
May 2015Paper3 ["SL"] · TZ19(a)[ 3 ]C1.1.5—Induced-fit binding
May 2015Paper3 ["SL"] · TZ29(a)[ 3 ]C1.1.5—Induced-fit binding
May 2013Paper3 ["SL"] · TZ1C2(b)[ 2 ]C1.1.5—Induced-fit binding
Practice this objective
Coverage 2011–2025 · Updated 15 Jul 2026
Induced Fit Improves Catalysis
In the induced-fit model, substrate binding causes a small active-site shape change that positions reactants and catalytic groups.
The flexible fit stabilizes the transition state and can strain bonds or exclude water. Binding is therefore more than a rigid lock-and-key match.
A useful induced-fit explanation includes:
- initial recognition
- conformational change
- transition-state stabilization
- product release
When substrate enters an enzyme pocket, side chains can rotate into a catalytic arrangement; products then leave because their interactions are weaker.
Induced fit does not mean every substrate binds equally well or that the enzyme permanently changes shape.
Induced-fit binding
Assessment in practice
2–3 marksHow it is assessed
This objective is assessed through structured response, commonly using Describe / Outline.
Command terms
Describe / Outline
What earns marks
Build the answer around this relationship: Induced fit involves a shape change when substrate binds.
Representative question
Question 1
Describe the lock and key model of enzyme activity and how the induced fit model extends it.
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
- Induced fit involves a shape change when substrate binds.
- The active site is not a perfect rigid match before binding.
- Conformational change can weaken substrate bonds and lower activation energy.
- Products leave and the enzyme can return to its active form.