Enzymes & Chemical Reactions

What is Energy???

LAWSFirst Law of Thermodynamics –

Energy is not created nor destroyed, just changed from one form to another

Second Law of Thermodynamics- Entropy always increases in a closed system. ie. Physical & chemical processes proceed in the direction that results in lower potential energy & increased disorder.

Free Energy ∆G - Change in free energy

Exergonic – Release of free energy. Spontaneous reactions and ∆G is less than zero.

Endergonic – Require input on energy. Non spontaneous and ∆G is greater than zero.

Enzymes & Catalysis

Transition state

Reactants

Products

Activation energy

Reactants

Products

Transition state

Ea with enzyme

∆G does not change

Induced Fit

Enzyme Substrate

Figure 3-22

A MODEL OF ENZYME ACTION

Substrates

Enzyme

Transition state

Shape changes

Products

1. Initiation: Reactants bind to the active site in a specific orientation, forming an enzyme-substrate complex.

2. Transition state facilitation: Interactions between enzyme and substrate lower the activation energy required.

3. Termination: Products have lower affinity for active site and are released. Enzyme is unchanged after the reaction.

Competitive Inhibition

Enzyme Substrate

Allosteric Regulation

Enzyme Substrate

Figure 3-25a

Enzymes from different organisms may function bestat different temperatures.

Glucose-6-phosphatase from bacterium that lives inside humans

Glucose-6-phosphatase from bacterium that lives in hot springs

Figure 3-25b

Enzymes from different organisms may function bestat different pHs.

Chitinase from bacterium that lives in acidic pools

Chitinase from soil-dwelling bacterium