When an enzyme is blocked, its substrate piles up
- The idea
- Predict
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- Why
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The idea
“If an enzyme is blocked, the product it makes will build up.”
It's easy to picture the product jammed at the block. The jam actually forms before the block, the way cars stack up before a closed road.
The short version
The mistake: If an enzyme is blocked, the product it makes will build up.
What's actually true: The substrate of the blocked step builds up. Its product, and everything made from that product, runs low.
- In a metabolic pathway, the product of one step is the substrate of the next. A substrate is the molecule an enzyme acts on.
- Block one enzyme and its substrate is no longer used up. Earlier steps keep making it, so it builds up.
- Its product stops being made. As the cell uses what it had, that product runs low, and so does everything after it.
- So if one compound rises while the next falls, the step between them most likely slowed.
On the exam: Find the blocked step. What it uses piles up. What it makes runs low.