3.1.2Inquiry Process
Enzyme Action — IB Biology HL Revision Notes & Topical Questions
5 min read 4 parts Lesson 102 of 160
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Part 1 of 4The Active Site and Induced Fit
Enzymes work by binding a substrate and lowering the energy needed for the reaction.
Active site
- Active site A small region on the enzyme surface, shaped by folding of the polypeptide, where the substrate binds and the reaction is catalysed.
Enzyme-substrate complex
- Enzyme-substrate complex The temporary structure formed when a substrate binds to the active site, in which the reaction takes place.
Induced fit
- Induced fit The active site changes shape slightly as the substrate binds, which makes the fit tighter and strains bonds in the substrate.
Products released
- Products released Once the substrate is converted, the products no longer fit well and leave the active site, which becomes free again.
Collisions
- Collisions Reaction needs random collisions between substrate and active site in the correct orientation,
- so conditions that increase collisions increase rate.
Part 2 of 4Factors Affecting Rate
Temperature
- Temperature Rate rises as molecules gain kinetic energy and collide more often with more energy, until the optimum temperature is reached.
Above the optimum
- Above the optimum High temperature breaks bonds that hold the tertiary structure, the active site changes shape and the enzyme is denatured.
pH
- pH Each enzyme has an optimum pH;
- away from it, charges on R groups change, bonding alters and the enzyme may denature.
Substrate concentration
- Substrate concentration Rate rises with substrate concentration because collisions become more frequent,
- then levels off when all active sites are occupied.
Enzyme concentration
- Enzyme concentration If substrate is in excess, more enzyme means more active sites and a faster reaction.
| Factor | Low value | Optimum | Very high or extreme |
|---|---|---|---|
| Temperature | Slow, few collisions | Maximum rate | Denatured, rate falls to zero |
| pH | Reduced activity | Maximum rate | Denatured |
| Substrate | Rate increases steeply | Active sites nearly full | Plateau at maximum rate |
Part 3 of 4Denaturation
Denaturation
Meaning
- Meaning A permanent change in the three-dimensional shape of a protein so that the active site no longer fits the substrate.
Causes
- Causes Heat and extreme pH disrupt hydrogen bonds and ionic bonds between R groups, which unfolds the tertiary structure.
Effect on rate
- Effect on rate A denatured enzyme cannot bind substrate, so the rate of reaction falls sharply or stops.
Plateau explanation
- Plateau explanation The graph for substrate concentration levels off because the enzyme is saturated, not because it has been denatured.
Part 4 of 4Exam Checklist & Tips
3.1.2 – Key Points for the Exam
- Active site The region of an enzyme where the substrate binds.
- Induced fit Change in the shape of the active site as the substrate binds.
- Denaturation Permanent loss of an enzyme's three-dimensional shape and function.
- Optimum The temperature or pH at which an enzyme works fastest.
- Saturation The state in which all active sites are occupied by substrate.
Common Mistakes
- Saying that cold temperatures denature enzymes;
- low temperature only slows them, and activity returns on warming.
- Explaining the plateau in rate as denaturation instead of saturation of active sites.
- Writing that the active site is a rigid lock; the induced fit model describes a flexible change.
- Stating that the enzyme is killed by heat; enzymes are not alive, they are denatured.
Last updated:
\n