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19 Cards in this Set
- Front
- Back
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Enzymes require cofactors such as..
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1.) iorganic ions: Fe2+, Mg2+, Mn2+ etc..
2.) organic/metallorganic molecules: coenzymes |
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Coenzymes
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transient carriers or specific atoms or functional groups
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Types of coenzymes
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prosthetic group: coenzyme/ metal tightly or covalently bonded to the enzyme protein
derived from vitamins |
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How do enzymes work?
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An enzyme like chymotrypsin has an active sit or pocket with amino acid residues. The residues have substituent groups that bind the substrate and catalyze its chemical transformation. The active site then encloses the substrate.
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favorable equilibrium: more P than S... however, it does not mean that..
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conversion will occur at a detectable rate
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activation energy
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difference between the free energy of the ground state and the transition state
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transition state
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fleeting moment where bond breakage, bond formation, and charge development have preceded to a point at which decay to either substrate or product is equally likely
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with no enzyme
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substrate: metal stick
transition state: bent stick products: broken stick |
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enzyme complementary to substrate
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enzyme (stickase) with a magnet-lined pocket complementary in structure to the stick (the substrate) stabilizes the substrate
bending doesnt happen because magnetic attraction between the stick and stickase enzyme |
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enzyme complementary to transition state
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an enzyme with a pocket complementary to the reaction transition state helps destabilize the stick, contributing to catalysis
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induced fit
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brings specific functional groups on the enzyme into a proper position to catalyze the reaction. the conformational change of the enzyme to fit the substrate permits formation of additional weak bonding interactions in the transition state.
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after substrate is bound to an enzyme, catalytic functional groups aid cleavage and formation of bonds by these mechanisms:
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1.) acid-base catalysis
2.) covalent catalyst 3.) metal ion catalyst they involve covalent interaction with a substrate to or from a substrate |
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general acid-base catalyst
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charged intermediates can be stabilized. -- transfer of protons to or from the substrate to form a species that breaks down more readily to products
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general acid-base catalyst
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definition: proton transfer mediated by other molecules
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general acid-base catalyst
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amino acid side chains can bind to the active site of the enzyme and act as proton donors or acceptors.. they allow proton transfers and provide rate enhancements.
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covalent catalysis
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covalent bond is formed between the enzyme and the substrate.
A--B +X:--> A--X +B (H2O)--> A+ X: +B amino acid side chains / functional groups of enzyme cofactors= nucleophiles |
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metal ion catalysis
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ionic interaction between enzyme bound material and substrate can stabilize charged reaction transition states
metals can change oxidation state |
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example of catalytic strategies combo
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chymotrypsin uses covalent /acid base catalysis
-- cleave peptide bond -- forms covalent linkage between a Ser residue on the enzyme and part of the substrate -- general base catalysis : other groups on the enzyme |
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SUMMARY
1) what are enzyme catalyzed reactions characterized by? 2) what is the function of enzymes? 3) is the equilibrium of a rxn affected by the enzyme? 4) energy used for enzymatic rate enhancements is derived from? 5.) catalysis involves what? |
1) formation of a complex between substrate and enzyme (ES complex)
2.) lower activation energy and speed reaction rate 3.) nope] 4) weak interactions (hydrogen bonds and hydrophobic and ionic interactions) between the substrate and enzyme. 5.) transient covalent interactions between the substrate and the enzyme or group transfers to and from the enzyme to provide a new lower energy reaction path |
