Enzymes
Introduced| English |
|---|
| enzyme/ˈenzaɪm/ |
| catalyst/ˈkætəlɪst/ |
| active site/ˈæktɪv saɪt/ |
| substrate/ˈsʌbstreɪt/ |
| activation energy/ˌæktɪˈveɪʃn ˈenədʒi/ |
Speeding up life's reactions
- Most reactions that keep you alive would happen far too slowly on their own.
- Digesting a meal could take years without help.
- Cells use special proteins to make these reactions fast enough.
- These proteins are enzymes — the catalysts of life.
Enzymes are catalysts
- An enzyme 酶 is a biological catalyst 催化剂.
- A catalyst speeds up a reaction without being used up itself.
- One enzyme molecule can be reused thousands of times.
- Almost every reaction in a cell has its own enzyme.
An enzyme is a biological…
An enzyme is a biological catalyst — it speeds up a reaction without being used up.
The active site
- Each enzyme has a pocket called the active site 活性位点.
- The substrate 底物 — the molecule it works on — fits into this pocket.
- The fit is specific, like a key in a lock.
- This is why each enzyme works on only one kind of substrate.
The substrate binds to which part of the enzyme?
The substrate fits into the enzyme's active site, like a key in a lock.
Lowering the activation energy
- Every reaction needs a starting push of energy — the activation energy 活化能.
- An enzyme lowers this energy barrier.
- With a smaller barrier, the reaction happens far faster.
- It can now run quickly at the gentle temperature of a living cell.
Enzyme rate and substrate
rate = Vmax·[S] / (Km + [S])
Drag the substrate. The rate rises then levels off at Vmax as every active site becomes busy.
Enzymes speed up reactions by lowering the activation energy.
By lowering the activation energy, an enzyme lets the reaction happen faster and at body temperature.
Select all true statements about enzymes.
Enzymes are not used up — they are reused. The other three are correct.
An enzyme is not used up in the reaction. It grabs the substrate, helps it react, then lets the product go — unchanged and ready to work again. This is why a cell needs only a tiny amount of each enzyme.
Because an enzyme is not used up, one enzyme molecule can be used over and ____.
A catalyst is reused, so a tiny amount of enzyme can process a huge number of substrate molecules.
Catalase, an incredibly fast enzyme:
- Your cells make hydrogen peroxide, a toxic waste.
- The enzyme catalase breaks it into harmless water and oxygen.
- A single catalase molecule can handle millions of peroxide molecules every second.
An enzyme is a biological catalyst that speeds up a reaction without being used up. The substrate binds to the enzyme's active site (a specific, lock-and-key fit), and the enzyme lowers the reaction's activation energy so it runs fast at body temperature.