What is meant by the term enzyme?
Reveal answer
A protein that acts as a biological catalyst.
Key words: enzyme
2(c) BIOLOGICAL MOLECULES · RECALL
2.10 Enzymes as biological catalysts
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What is meant by the term catalyst?
Reveal answer
A substance that increases reaction rate without being used up overall.
Key words: catalyst
What is meant by the term substrate?
Reveal answer
A reactant molecule upon which an enzyme acts.
Key words: substrate
What is meant by the term active site?
Reveal answer
The region of an enzyme where the substrate binds and catalysis occurs.
Key words: active site
What is meant by the term activation energy?
Reveal answer
The minimum energy barrier that reacting particles must overcome.
Key words: activation energy
What is meant by the term enzyme–substrate complex?
Reveal answer
The temporary association formed when substrate binds to an enzyme.
Key words: enzyme–substrate complex
Following one catalytic cycle: for 1. Collision, give the molecular event and the significance.
Reveal answer
Molecular event: Substrate reaches the active site in a suitable orientation. Significance: A successful collision becomes possible.
Key words: 1. Collision
Following one catalytic cycle: for 2. Binding, give the molecular event and the significance.
Reveal answer
Molecular event: An enzyme–substrate complex forms. Significance: Interactions position and strain reacting groups.
Key words: 2. Binding
Following one catalytic cycle: for 3. Catalysis, give the molecular event and the significance.
Reveal answer
Molecular event: Bonds break or form through a lower-activation-energy pathway. Significance: The reaction proceeds faster.
Key words: 3. Catalysis
Following one catalytic cycle: for 4. Release, give the molecular event and the significance.
Reveal answer
Molecular event: Products leave the active site. Significance: The unchanged enzyme is available again.
Key words: 4. Release
True or false, and why? “Enzymes give reactions energy.”
Reveal answer
False. They lower the activation-energy barrier; they do not create or supply energy.
True or false, and why? “An enzyme is used up each time it works.”
Reveal answer
False. It is regenerated after product release and can catalyse repeated cycles.
True or false, and why? “The lock-and-key model is a literal picture.”
Reveal answer
False. It is a simplified model; real proteins move and active sites can change conformation.
True or false, and why? “All enzymes break molecules down.”
Reveal answer
False. Enzymes catalyse both breakdown and synthesis reactions.
How does an enzyme speed up a reaction?
Reveal answer
Substrate binds to the active site → enzyme–substrate complex forms → less activation energy is needed.
Key words: active site · activation energy