Interactions between substrate and active site to allow induced-fit binding
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Question
What type of molecule is an enzyme?
Answer
A **globular protein** that acts as a **biological catalyst**.
Question
Define a catalyst.
Answer
A substance that **speeds up a reaction** without being used up, so it can be **reused**.
Question
What is the active site?
Answer
The specific **pocket on an enzyme's surface** where the substrate binds; its shape is **complementary** to the substrate.
Question
What is a substrate?
Answer
The **reactant molecule** that an enzyme acts on.
Question
What is an enzyme-substrate complex?
Answer
The temporary structure formed when a **substrate is bound** to an enzyme's **active site**, just before the reaction.
Question
Why is each enzyme specific?
Answer
Its **active site is complementary** in shape to **only one substrate**, so only that substrate can fit and bind.
Question
What does the induced-fit model state?
Answer
As the substrate binds, the **active site changes shape slightly** to **mould around it**, helping the reaction occur.
Question
How does induced fit differ from lock-and-key?
Answer
Lock-and-key has a **rigid** active site; induced fit has a **flexible** active site that **moulds** around the substrate.
Question
Which binding model does the IB accept as current?
Answer
**Induced fit** — the lock-and-key model is older and superseded.
Question
What happens to an enzyme after the reaction?
Answer
It is **unchanged** — the products leave and the enzyme can be **reused**.
Question
Name three features shared by all enzymes.
Answer
They are **globular proteins**, **biological catalysts**, and each has a **specific active site** (also: specific, reusable/unchanged).
Question
If an enzyme forms a product with only one of several molecules, why?
Answer
Only that molecule's shape is **complementary** to the **active site**, so only it can bind and react.
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Topic 3.1 hub
Enzymes and metabolism
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