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Unformatted text preview: Lecture 5 Lecture 5: Enzyme Catalysis and Regulation Catalytic Power and Specificity of Enzymes F.G on enzyme form transient covalent bonds with a substrate and activate it for reaction; or group is transiently transferred from the substrate to the enzyme These covalent interactions lower the activation energy Formation of weak interaction in the ES complex is accompanied by release of small amt. of free energy that stabilizes; this energy is the binding energy ( G b ) Binding energy is the main source of free energy used by enzymes to lower the activation energies of reactions How enzymes use noncovalent binding energy: a) free energy released in forming many weak bonds and interactions between enzyme and substrate b) enzyme active sites are complementary to transition states, not substrates Transition State Lock and key model is poor because the ES complex is more stable and has less free energy in the ground state than substrate alone Pauling: enzyme must be complementary to the reaction transition state The free energy (binding energy) released by the formation of these interactions partially offsets the energy required to reach the top of the energy hill Weak binding interactions between the enzyme and substrate provide a strong driving force for catalysis Decent binding achieved by positioning substrate in a cavity where it is effectively removed from water The binding energy gives an enzyme its specificity: derived from formation of many weak interaction between the enzyme and its specific substrate- physical and thermodynamic factors contribute to G (barrier to reaction): o reduction in entropy (decreased freedom of motion of 2 molecules in solution) o solvation shell of hydrogen-bonded water that surrounds and stabilizes most biomolecules in solution o distortion of substrates that must occur in reactions o need for proper alignment of F.G on enzyme- Entropy reduction is obvious benefit of binding to enzyme; Binding energy holds the substrates in the proper orientation o When two reacting groups are in a single molecule, the reaction is much faster o The more rigid and closely aligned reaction groups are, the more likely they will react- Desolvation: weak bonds between substrate and enzyme- Enzyme-substrate interactions replace most or all of Hbonds between substrate and water Lecture 5- Binding energy with weak interactions formed only in transition state compensate thermodynamically for any distortion, primarily electron redistribution- Enzyme undergoes conformation change after binding: induced fit: specific F.G Enzyme undergoes conformation change after binding: induced fit: specific F....
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