lecturenoteschap6-10-1slide

lecturenoteschap6-10-1slide - BCMB/BIOL/CHEM 3100 Chapter...

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BCMB/BIOL/CHEM 3100 hapter 6 Mechanisms of Enzymes Chapter 6 Mechanisms of Enzymes Energy diagrams Chemical modes of enzyme catalysis Acid-Base catalysis Covalent catalysis Binding modes of enzyme catalysis roximity effect Proximity effect Transition state stabilization ransition state analogs Transition state analogs Induced fit erine Proteases 1 Serine Proteases
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Energy diagrams show the progress of a reaction : high _______________ g energy, unstable state in which a molecule is best it d t d suited to undergo a chemical reaction; state in which chemical bonds are being broken and formed. Lifetime ~ 10 -14 to 10 -13 sec Fig 6.1 Energy diagram 2 for a single-step reaction
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Fig 6.2 Energy diagram for reaction with intermediate • __________ occurs in the trough between the two transition states • Lifetime > ~10 -14 to 10 -13 sec • In this case, the rate determining step in the forward direction is formation of the first 3 transition state
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Fig 6.3 Enzymatic catalysis of the reaction A+B A-B Proximity effect: “proper” positioning of substrates Transition state stabilization : lowers activation energy 4
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hat is the enzyme active site? What is the enzyme active site? A few polar residues and H 2 O molecules are found at the otherwise hydrophobic active site of an enzyme ______________ : polar amino acids that ndergo changes during enzymatic catalysis undergo changes during enzymatic catalysis Ionic side chains are involved in two types of chemical catalysis: . 5 1. _______________ 2. _______________
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Table 6.1 Note: pKa of ionizable groups of amino acids in proteins vary 6 from pKa of free amino acids (compare Table 3.2 to Table 6.2)
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Table 6.2 pKa Values of amino acid ionizable groups in proteins Group pK a Terminal -carboxyl 3-4 Side-chain carboxyl 4-5 Imidazole 6-7 Terminal -amino 7.5-9 hiol 5 Thiol 8-9.5 Phenol 9.5-10 mino 10 -Amino ~10 Guanidine ~12 7 Hydroxymethyl ~16
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Chapter 6 Mechanisms of Enzymes Energy diagrams Chemical modes of enzyme catalysis Acid-Base catalysis Covalent catalysis Binding modes of enzyme catalysis roximity effect Proximity effect Transition state stabilization ransition state analogs Transition state analogs Induced fit erine Proteases 8 Serine Proteases
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Chemical modes of enzyme catalysis Acid-Base catalysis y Covalent catalysis 9
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_________________: acceleration of a reaction by transfer of a protein B: = base (proton acceptor) BH+ = conjugate acid (proton donor) •A general base ( B: ) can act as a proton acceptor to remove protons from OH, NH, CH or other XH his produces a stronger nucleophilic reactant (X: - This produces a stronger nucleophilic reactant (X: ) 10
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General base catalysis reactions (continued) • A _____________ ( B: ) can remove a proton from water and thereby generate the equivalent of OH - in neutral solution 11
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roton donors can also catalyze reactions Proton donors can also catalyze reactions •A ____________ ( BH + ) can donate protons
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lecturenoteschap6-10-1slide - BCMB/BIOL/CHEM 3100 Chapter...

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