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Lecture 5

Biochemistry 2280A Lecture 5: 5 - Enzyme Catalysis

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Biochemistry 2280A
Eric Ball

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find more resources at Tuesday, September 22, 2015 Enzyme Catalysis Meakin Lecture 6 By the end of today: - describe what an enzyme is and how it accelerates biochemical reactions - understand the different types of reactions that enzymes can perform - understand what catalysts do Enzyme Catalysis - biological catalysts • perform nearly all chemical transformations in cells • accelerate, but are unchanged by, a reaction - most enzymes are proteins - name often ends in 'ase‘ (eg. protease) - often extremely specific • they have ‘targeted’ or restricted ligands (called substrates) • substrate: the molecule on which an enzyme acts - enzymes carry out a limited number of chemical reactions Types of Chemical Reactions Carried Out by Enzymes - hydrolytic — cleavage using water • nucleases, proteases, phosphatases - condensation — connect molecules together • polymerases, synthases - isomerization — rearrange bonds • isomerases - oxidation-reduction — gain or loss of electrons • oxidases, reductases, dehydrogenases - group transfer — transfer chemical group • phosphorylation, sumolyation, acetylation, glycosylation Enzymes Act On But Are Unchanged By Substrates Active Site of Enzymes - part of the enzyme where the reaction takes place • small part of enzyme surface (5% or less) • often a cleft or crevice between domains - substrate binds in active site • multiple weak bonds • dissociates from enzyme ▯1 find more resources at find more resources at Tuesday, September 22, 2015 How Do Enzymes Catalyze Reactions? - must understand a transition state - the transition state of a chemical reaction is defined as the state corresponding to the highest energy along the reaction coordinate - at this point, assuming a perfectly irreversible reaction, colliding reactant molecules will always go on to form products - the transition state is: • an intermediate form between reactants and products • a transient, high-energy state • a form different from reactants & products Enzyme Catalysis - the speed of a reaction is determined by how difficult it is to get to the transition state - enz
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