Study GuideBiochemistry I–Enzymes1.Chemical Mechanisms of Enzyme CatalysisEnzymes can speed up chemical reactions by anextraordinary amount—sometimes by as much asa billion times. However, there is a physical limit to how fast an enzyme can work. An enzyme cannotcatalyze reactions faster than it canencounter its substrate.In solution, enzymes collide with substrates at a rate of about10⁸–10⁹ times per second. Inside cells,enzymes that act in the same metabolic pathway are often positioned close together. Thisarrangement reduces the need for substrates to diffuse long distances and makes reactions evenmore efficient.Even so, enzymes remain incredibly powerful catalysts because they use several cleverchemicalmechanismsto speed up reactions.1.1The Transition StateFor any chemical reaction to occur, reactant molecules must pass through ahigh-energyintermediate formcalled thetransition state.•During a reaction, the energy of molecules temporarily increases•The transition state is unstable and short-lived•Once molecules pass this state, they can form productsThis explains why reactions usually happen faster at higher temperatures—more molecules can reachthe transition state.On an energy diagram, the transition state appears as anenergy barrier or hill.Catalysts, including enzymes, speed reactions by lowering this barrier, making it easier to reachthe transition state.Preview Mode
This document has 33 pages. Sign in to access the full document!