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17 Cards in this Set
- Front
- Back
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5 Types of Catalytic Mechanisms |
Acid-base catalysis Covalent catalysis Metal ion catalysis Proximity and orientation effects Preferential binding of the transition state complex |
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General Acid Catalysis |
A process in which proton transfer from an acid lowers the free energy of a reaction's transition state. |
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General base catalysis |
A reaction may also be stimulated by general base catalysis if its rate is increased by proton abstraction by a base. |
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Amino acids residues with pK's near the physiological pH range |
Asp, Glu, His, Cys, Tyr, Lys
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Why is acid-base catalysis a common enzymatic mechanism? |
Due to the ability of enzymes to arrange several catalytic groups around their substrates makes concerted acid-base catalysis a common enzymatic mechanism. |
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What is covalent catalysis? |
Covalent catalysis accelerates reaction rates through the transient formation of a catalyst-substrate covalent bond. |
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3 Stages of covalent catalysis |
1. The nucleophilic reaction between the catalyst and the substrate to form a covalent bond. 2. The withdrawal of electrons from the reaction center b the now electrophilic catalyst. 3. The elimination of the catalyst, a reaction that is essentially the reverse of stage 1. |
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3 major ways metal ions participate in the catalytic process: |
1. By binding to substrates to orient them properly for reaction. 2. By mediating oxidation-reduction reactions through reversible changes in the metal ion's oxidation state. 3. By electrostatically stabilizing or shielding negative charges. |
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Catalysis through Proximity and Orientation Effects |
1. Bring substrates into contact with catalytic groups. (inc. 5) 2. Bind substrates in the proper orientation for reactions. (inc. 100) 3. Charged groups stabilize the transition state. 4. Freeze out the relative translational and rotational motions ( inc. 10^7) |
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Enzymes catalyze reactions by preferentially binding the transition state |
An enzyme may bind the transition state of the reaction it catalyzes with greater affinity than its substrates or products. Enzymes that preferentially bind the transition state structure increase its concentration and therefore proportionally increase the reaction rate. |
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Lysozyme |
An enzyme that destroys bacterial cell walls. Hydrolyzes Beta(1->4) glycosidic linkages from N-acetylmuramic acid (NAM or MurNAc) to N-acetylglucosamine (NAG or GlcNAc) in cell wall peptidoglycans. |
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Lysozyme's Catalytic Site |
Determined through modeling. 30 X 30 X 45 A Most striking feature is a prominent cleft, the substrate-binding site, that traverses one face of the molecule. |
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What reaction is catalyzed by the lysozyme? |
The hydrolysis of a glycoside, the conversion of an acetal to a hemiacetal. |
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What are lysozymes catalytic residues? |
Glu 35 and Asp 52 |
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Schiff Base |
Is an electron sink. Electron sinks pull electrons towards them. |
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Nucleophiles |
Electron pair or negative charge Hydroxyl group(RO), sulfhydryl group (RS), Amino group(RNH2), Imidazole group |
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Electrophiles |
Electron-deficient atoms Protons (H+), Metal ions( M+), Carbonyl Carbon atom, Cationic imine (schiff base) |
