Endergonic reaction: requires energy, usually ATP Exergonic reaction: releases energy, occurs spontaneously energy + reactants products + Endergonic and Exergonic Reactions energy products + + ∆G > 0 reactants ∆G < 0
An exergonic reaction If exergonic reactions occur spontaneously, why isn’t the paper in front of you on fire?
Just as the person may need a push to get started down a hill, many of the exergonic reactions that living organisms depend on for survival may need a “push”. ∆G < 0
Figure 6.12 Energy profile of an exergonic reaction EA = activation energy
Example of an enzyme-catalyzed reaction: Hydrolysis of sucrose energy +
In living organisms the “somethings” that provide that push are called enzymes Without enzyme: With enzyme:
Most enzymes are protein molecules with a specific 3-dimensional shape Active site substrate enzyme “induced fit”
Enzymes catalyze reactions in living organisms: 1. Bring reactant molecules close together 2. Make bonds easier to break/form
Enzymes only increase the rate of exergonic reactions, they can’t cause non-spontaneous reactions to occur Only the substrate will be altered, the enzyme will be released to work again Enzymes are one type of catalyst Notes about enzymes
Binding of enzyme and substrate Temperature at which the enzyme functions What determines how well an enzyme works?
Does the same enzyme show variation from one individual to another? Is the form of enzyme an individual produce a heritable trait? Does the form of enzyme individual produce affect its survival/reproduction? Can a species’ enzymes be shaped by natural selection?