MCB 450 1st Edition Lecture 10 Outline of Last Lecture I Membrane Proteins a peripheral b integral c lipid anchored II Membrane Transport Outline of Current Lecture I Principles of Enzyme Catalysis a Free Energy and Equilibria b Keq and G in Living Cells c Activation Energy d Enzyme Substrate Interaction Current Lecture Chemical reactions in cells In a living cell thousands of reaction have to go on 7 10 fold rate enhancement by carbonic anhydrase One of the fastest enzymes known o Very important in our physiology Rate enhancements by enzymes Don t have to know all of these rates and rate enhancements by emphasizes a number of different points More about enzymes Activity of enzymes can be turned up or turned down as needed Classes of enzymes Enzymes have classification numbers o E g trypsin 2 4 21 4 chymotrypsin 3 4 21 1 Exam questions may have to do with recognizing a reaction and labeling it Enzyme cofactors Not required to memorize the list of enzyme cofactors at this point Some thermodynamic considerations Two different thermodynamic properties that we must consider o Delta G free energy change o The free energy Predicting spontaneity of a reaction from delta G These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Reaction is written to be reversible Have to define in which direction you are going with the reaction Progress curve for an exergonic reaction Exergonic reaction release energy o Will proceed spontaneously Progress curve for endergonic reaction Endergonic reaction input of energy needed o Will not proceed spontaneously Delta G indicates whether the reaction will be spontaneous or not but will not tell us anything about the rate of the reaction More thermodynamic considerations Want to relate delta G to the equilibrium constant How do we measure free energy change delta G You ll be given the value of R on the exam R the gas constant Biochemical standard free energy change Delta G zero prime is more realistic in its use in biochemistry Relation between delta G zero prime and K eq Product formation favored Talking about the standard free energy under a set of standardized conditions Actual concentrations of A B can modify delta G in living cells Under non equilibrium conditions In a living cell it is normally away from equilibrium or at non equilibrium Enzymes accelerate the reaction rate but do not affect the position of the equilibrium Enzyme allows the reaction to reach equilibrium much faster Enzymes facilitate formation of the transition state Transition state least stable intermediate in the reaction Concepts Know definitions o Active site o Enzyme substrate complex o Binding energy Binding energy key to lowering activation energy Active site amino acids may include amino acids that are widely separate in the 1 sequence Shows N to C terminus Makes a point that side chains tend to be positioned on the loops Lock and key model of substrate binding Aren t a rigid lock and key arrangement The active site will change shapes Enzymes are complementary to transition state not substrate Metal stick analogy Groups that will interact with the substrate are shown in red Enzymes are complementary to transition state Can we use this to develop drugs