Enzymes Organic Catalysts Chemical Reactions Every chemical reaction

Enzymes Organic Catalysts

Chemical Reactions �Every chemical reaction between molecules involves bonds breaking and bonds forming. �Changing one molecule into another generally involves contorting the starting molecule into a highly unstable state before the reaction can proceed. �To reach this state, reactant molecules must absorb energy from their surroundings. �When new bonds are formed, energy is released as heat and the molecules return to a stable conditions with lower energy.

�The Energy Profile of an Exergonic Reaction for a hypothetical reaction AB + CD To each rthis state AC + BD EA = activation energy

Enzymes �Enzymes are organic catalysts. �Involved in chemical reactions but not altered by them. �Many enzymes function by lowering the activation energy.

Enzymes decreases EA 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 Induced Fit Model

Enzyme (Lock & Key Model) �Enzymes bind temporarily to one or more of the reactants — the substrate(s) — of the reaction they catalyze. In doing so, they lower the amount of activation energy needed and thus speed up the reaction. �

How Enzymes Work �Enzymes lower the activation Energy (EA) by weakening bonds in the substrate molecule + energy

Factors that affect enzyme activity �The activity of enzymes is strongly affected by changes in �p. H �Temperature �Concentration of Enzyme �Concentration of Substrate �Each enzyme works best at a certain temperature and p. H, its activity decreasing at values above and below that point.

Figure 6. 16 Environmental factors affecting enzyme activity