Temperature, pH and substrate concentration
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Flip to reveal answersWhat three factors affect the rate of an enzyme-controlled reaction?
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All 12 Flashcards — Temperature, pH and substrate concentration
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Question
What three factors affect the rate of an enzyme-controlled reaction?
Answer
**Temperature**, **pH** and **substrate concentration**.
Question
What is the optimum temperature of an enzyme?
Answer
The temperature at which the enzyme works **fastest** — the peak of the rate-versus-temperature graph.
Question
Why does enzyme rate rise as temperature increases (below the optimum)?
Answer
Molecules move **faster**, so the substrate **collides with the active site more often**, increasing the rate.
Question
Why does enzyme rate fall above the optimum temperature?
Answer
The enzyme is **denatured** — the **active site changes shape**, so the substrate no longer fits.
Question
What is denaturation?
Answer
A (usually permanent) change to the **shape of the active site**, caused by high temperature or extreme pH, that stops the enzyme working.
Question
What does a rate-versus-pH graph look like, and why?
Answer
A single **peak** at the **optimum pH**; the rate falls either side because the wrong pH **denatures** the enzyme (distorts the active site).
Question
Why does the rate plateau at high substrate concentration?
Answer
All the **active sites are occupied** (the enzymes are **saturated**), so extra substrate cannot speed up the rate.
Question
What is saturation?
Answer
The point where **every active site is occupied** by substrate, so adding more substrate does not increase the rate.
Question
At the plateau on the substrate graph, what is the limiting factor?
Answer
The **number of enzyme molecules** (active sites) — not the amount of substrate.
Question
How is denaturation different from saturation?
Answer
**Denaturation** changes the active-site **shape** (rate falls, enzyme ruined); **saturation** means all sites are **full** (rate plateaus, enzyme unharmed).
Question
On a temperature graph, how do you score the explanation of the falling part?
Answer
Name **denaturation** AND give the mechanism: the **active site changes shape so the substrate no longer fits**.
Question
When explaining a data graph, what two things must your answer contain?
Answer
The **trend** read off the graph **and** the biological **reason** for it.
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Topic 3.1 hub
Enzymes and metabolism
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