ENZYMEShandouts - ENZYMES as biological catalysts in...

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ENZYMES as biological catalysts in chemical reactions
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Three criteria must be met for a chemical reaction to occur: The reactants, called substrates must collide The molecular collision must occur with the correct orientation The reactant must have sufficient energy. This energy is called the activation energy
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Enzymes are Biological Catalysts Enzymes are proteins that: Increase the rate of reaction by lowering the energy of activation. Catalyze nearly all the chemical reactions taking place in the cells of the body. Have unique three-dimensional shapes that fit the shapes of reactants.
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The formation of the enzyme-substrate complex (ES) decreases the activation energy for the reaction by placing the substrates in a position that is accessible to the catalytic apparatus
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Enzyme Catalyzed Reaction
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The active site : Is a region within an enzyme that fits the shape of molecules called substrates . Contains amino acid R groups that align and bind the substrate. Releases products when the reaction is complete. Active Site
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Some key features of the active site The active site takes up a relatively small part of the total volume of an enzyme The active site is a three-dimensial entity Substrates are bound to enzymes by multiple weak attraction Active sites are clefts or crevices The specificity of binding depends on the precisely defined arrangement of atoms in an active site
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The substrate binding site The substrate binding site is a particular arrangement of chemical groups on the enzyme surface that is specially formulated to bind a specific substrate The substrate binding site may have been integrated within it the active site or in some cases the active site may not be within the substrate binding site
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The allosteric site The allosteric site is not at the active site or substrate binding site, but is somewhere else on the molecule The allosteric site is the site where small molecules bind and affect a change in the active site or the substrate binding site The binding of this specific molecule causes a change in the conformation of enzyme what cause the active site to become either more or less active It may cause the binding site to have a greater affinity for substrate or have less affinity for substrate
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