Inorganic Phosphate Enzymes Harnessing Energy The key to effective use of

Inorganic phosphate enzymes harnessing energy the key

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Inorganic Phosphate
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Enzymes-- Harnessing Energy The key to effective use of energy in metabolism is to harness as much energy as possible at every step of a catabolic pathway A B C D Enzyme 1 Enzyme 2 Enzyme 3 substrate substrate substrate substrate energy energy energy energy At the top, all the energy is expended in one step. At the bottom the energy is captured in a series of steps, analogous to an enzymatic pathway.
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Energy profile of a reaction Because large molecules are unstable, they must be protected against spontaneous breakdown. Without the required input of activation energy, all exergonic reactions would occur at once. Activation energy enables cells to control the timing of exergonic reactions. Activation energy (E A ) Activation Energy is energy required to break bonds in reactants and initiate a spontaneous reaction E A repaid in exergonic reactions
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Cells use enzymes to lower Energy of Activation With an enzyme mediating, less activation energy is required to start a reaction, but there is no change in the ΔG (i.e., no loss of output energy) Enzymes are catalysts: they speed-up spontaneous reactions, but they are not consumed in the process
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Catalytic cycle of an enzyme Enzyme terms: Substrate : reactant molecule Active site : area of the enzyme to which the substrate attaches To reduce the activation energy of a spontaneous reaction, an enzyme may… 1. Stress key bonds 2. Orient the substrate with other reactants (that’s what’s happening here) 3. Provide a microenvironment conducive to reaction (that could also be happening here) 4. React briefly with a substrate to form a reactive intermediate induced fit-- squeezably snug
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Factors influencing enzyme "activity" Temperature Heat speeds enzyme activity (up to a point). Too much heat could deactivate the enzyme. A change in pH May activate or deactivate enzymes Cofactors These are non-protein enzyme helpers. Coenzymes are organic cofactors
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Enzyme inhibition competitive inhibitor non-competitive inhibitor Enzymes promote reactions, so they must be turned off when reactions are undesirable . Biological purpose of enzyme inhibition—to control enzyme expression—i.e., to turn enzymes either on or off. Practical purposes of enzyme inhibition— Artificial inhibition of enzymes can be useful in medicine and agriculture. E.g., DDT inhibits enzymes of an insect’s nervous system.
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allosteric site Allosteric regulation causes changes in the active site by binding enzymes at a site other than the active site. Sometimes allosteric binding increases enzyme activity, e.g., when a cell requires more of some kind of product. Allosteric regulation
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Feedback inhibition Feedback inhibition occurs when the end product inhibits an enzyme pathway. In this case, the enzymatic pathway is anabolic ; it is constructing isoleucine from threonine via a series of enzymatic steps, each of which requires energy input in the form of ATP . However, when the cell has enough isoleucine, it needs to shut down the anabolic pathway to save ATP and threonine. Thus, the end product, isoleucine, interferes with enzyme 1, shutting down the pathway that makes it. ATP ATP ATP ATP ATP
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