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Enzymes
Enzymes are proteins that catalyze biochemical reactions.
- They have the ability to change the rate of the reaction (i.e. they make slow reactions faster).
- Enzymes are types of catalysts. This means they help a reaction, but they are not used up in the process of the reaction.
- The name of an enzyme ends with "ase." Example: Synthase, lactase.
- Enzymes lower the activation energy of reactions (EA) which means they lower the energy required for the reaction to occur.
- They DO NOT change a reactions free energy (ΔG).
- They work by stabilizing the transition state:
(transition state)
Enzymes Specificity
Enzymes are specific to one (or a few) substrates, and have an active site that binds to its particular substrate.
- Induced fit – active site changes upon substrate binding for better fit/catalysis.
- The active site holds the molecules in a position that promotes a reaction to occur.
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Enzyme Activity
Enzyme Activity And Its Effect On the Rate of a Reaction
The activity of an enzyme can be affected by other factors in the body.
- Substrate concentration ––> the more substrate (substance reacting), the faster the reaction rate is going to be. Analogy: a cashier is only busy when there are customers around.
- Temperature and pH ––> Enzymes often only work at a specific temperature and pH. If they don't have the correct environment, they will denature (loose its shape). Example: pepsin (stomach enzyme) works best at pH 2.0.
- Enzyme activity can be helped by cofactors or coenzymes (small helper molecules). Example: cofactors include vitamin B6, zinc, and magnesium (these are NOT proteins).
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Example: Enzyme Catalysis
Which line below represents the enzyme-catalyzed reaction, blue or pink?
The blue line shows an enzyme catalyzed reaction. The activation energy has been lowered.
Practice: Enzymes and Delta G
Enzymes lower the overall delta G of a reaction, true or false?