Enzymes

Enzymes are catalysts:

• Catalysts are agents that increase the rate of chemical reactions.
• They reduce the activation energy.
• These reactions would happen anyway.
• Enzymes increase the rates millions of times.
• Enzymes are very specific for the substrate on which the act.
• Substrate is the specific molecule that the enzyme acts on.

Enzyme Cycle

• Physical conformation (shape) of enzyme is crucial.
• On the enzyme is the active site into which the substrate fits.
• The substrate fitting into the enzymes causes the enzyme to change its shape, an induced fit.
• This also induces stress on the substrate and allows for bonds to be broken easier.

Factors Affecting Enzyme Action

• Enzymes function within a narrow range of pH and temperature.
• May require nonprotein cofactors.
• Competitive inhibitors will block the active site.
• Noncompetitive inhibitors bind to enzyme and cause shape change. Examples: some pesticides and antibiotics.
• Some enzymes have allosteric sites. When an allosteric regulator binds to this site the entire conformation of the enzyme changes.

Feedback regulation

• Think of the enzyme cycle as a pathway.
• A metabolic end product can act as an inhibitor for an earlier enzyme path.