Enzymes
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31 Terms
What is an enzyme?
A biological catalyst that speeds up chemical reactions without being used up.
What type of molecule are enzymes?
Proteins.
What does a catalyst do?
Increases the rate of a chemical reaction.
What is the active site?
The part of the enzyme where the substrate binds.
Why are enzymes specific?
Their active sites have a complementary shape to the substrate.
What is a substrate?
The molecule an enzyme acts on.
What is an enzyme–substrate complex?
A temporary structure formed when substrate binds to enzyme.
Lock-and-key model
Substrate fits exactly into a rigid active site.
Induced-fit model
Active site changes shape slightly when substrate binds.
Which model is more accepted?
Induced-fit model.
What is activation energy?
The minimum energy needed to start a reaction.
How do enzymes lower activation energy?
By bringing substrates together and weakening bonds.
Do enzymes change the overall energy of a reaction?
No.
What is the optimum temperature for human enzymes?
About 37°C.
What happens to enzymes at high temperatures?
They become denatured.
What is denaturation?
Permanent change in enzyme shape causing loss of function.
What is optimum pH?
The pH at which an enzyme works best.
Optimum pH of amylase
About pH 7.
Optimum pH of pepsin
About pH 2.
Effect of increasing substrate concentration
Rate increases until enzymes are saturated.
What is enzyme saturation?
All active sites are occupied.
Effect of increasing enzyme concentration
Reaction rate increases if substrate is available.
What is enzyme inhibition?
Reduction of enzyme activity.
Competitive inhibition
Inhibitor competes with substrate for the active site.
How to reduce competitive inhibition
Increase substrate concentration.
Non-competitive inhibition
Inhibitor binds away from active site and changes enzyme shape.
Can non-competitive inhibition be reversed?
No.
What is a cofactor?
An inorganic ion needed for enzyme activity.
Example of a cofactor
Magnesium ion (Mg²⁺).
What is a coenzyme?
An organic molecule that helps enzyme action.
Example of a coenzyme
NAD or FAD.