What are the optimum pH values of salivary amylase and stomach protease?
Reveal answer
Salivary amylase about pH 7; stomach protease (pepsin) about pH 2.
Key words: pH 7 · pH 2
2(c) BIOLOGICAL MOLECULES · RECALL
2.13 pH and enzyme function
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Explain why extreme pH stops an enzyme working.
Reveal answer
pH changes the bonds holding the protein’s shape; the active site changes shape so the substrate no longer fits (denatured).
Key words: active site · denatured
What is the optimum pH?
Reveal answer
The pH at which an enzyme works fastest.
Key words: optimum
Does extreme pH increase kinetic energy like temperature does?
Reveal answer
No. pH only affects the shape of the enzyme (active site); temperature affects both collision rate and shape.
Key words: shape
What is meant by the term pH?
Reveal answer
A logarithmic measure related to hydrogen-ion concentration.
Key words: pH
What is meant by the term optimum pH?
Reveal answer
The pH producing the highest measured activity under specified conditions.
Key words: optimum pH
What is meant by the term tertiary structure?
Reveal answer
The overall three-dimensional folding of one protein chain.
Key words: tertiary structure
pH effects from particles to graph: for Solution, give the change and the consequence.
Reveal answer
Change: Hydrogen-ion concentration changes. Consequence: Amino-acid side-chain protonation changes.
Key words: Solution
pH effects from particles to graph: for Protein, give the change and the consequence.
Reveal answer
Change: Charges and stabilising interactions change. Consequence: Active-site shape or chemistry changes.
Key words: Protein
pH effects from particles to graph: for Binding/catalysis, give the change and the consequence.
Reveal answer
Change: Fewer productive enzyme–substrate complexes form. Consequence: Product formation per second decreases.
Key words: Binding/catalysis
pH effects from particles to graph: for Extreme pH, give the change and the consequence.
Reveal answer
Change: Tertiary structure is substantially disrupted. Consequence: The enzyme denatures and may not recover.
Key words: Extreme pH
True or false, and why? “pH changes the substrate into an enzyme.”
Reveal answer
False. pH changes molecular charge and can alter enzyme structure or binding.
True or false, and why? “Every enzyme works best at pH 7.”
Reveal answer
False. Optimum pH depends on the enzyme and its usual environment.
True or false, and why? “Any small pH change permanently denatures an enzyme.”
Reveal answer
False. Moderate changes may reduce binding reversibly; sufficiently extreme pH can cause denaturation.
True or false, and why? “Pepsin works in acid because acid digests the protein for it.”
Reveal answer
False. Pepsin itself catalyses protein hydrolysis; acidic conditions support its active-site structure and chemistry.