Enzyme kinetics
How reaction speed depends on substrate amount. Speed rises, then levels off at Vmax when every active site is busy. Km is the substrate level giving half of Vmax.
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Analogy
A bank with a fixed number of tellers: more customers help until all tellers are busy.
Example
Substrate low: speed climbs.Substrate high: speed flat at Vmax.Km = substrate at half Vmax.
In practice
A low Km means the enzyme grabs its substrate even when it is scarce.
Practice
Flashcards
- What do Vmax and Km mean?Vmax is the top speed when all active sites are busy. Km is the substrate level at half of Vmax.
Interview questions
- Compare competitive and non-competitive inhibition, saying how each shows up on a rate-versus-substrate curve.
- Competitive binds the active site
- Non-competitive binds elsewhere
- Competitive: Vmax same, apparent Km rises
- Non-competitive: Vmax falls
Questions people ask
What does the Michaelis-Menten equation describe?
It describes how reaction rate depends on substrate concentration for a simple enzyme. The rate equals Vmax times substrate, divided by Km plus substrate. It gives the curve that climbs and flattens. Biochemists use it to compare enzymes and to measure how drugs affect them.
Besides substrate, what else changes enzyme rate?
Enzyme concentration, temperature and pH all matter. More enzyme means a higher Vmax. Each enzyme has an optimum temperature and pH where its shape is best. Pepsin in the stomach works at about pH 2, while most enzymes in the blood work near pH 7.4.