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Chapter 8.3 Notes EQ
What Are Enzymes ? - Catalysts: substances that speed up reactions without themselves being permanently altered. Catalysts increase the rate of reactions but does not cause a reaction to occur. - Biological catalysts are called enzymes. A biological catalyst is a framework or scaffold within which chemical catalysis takes place. The process does not permanently alter the structure.
Explain how the structure of an enzyme makes that enzyme specific.
To speed up a reaction, an energy barrier must be overcome - An exergonic reaction may release a great deal of free energy, but take place very slowly. Such reactions are slow because there is an energy barrier between reactants and products. -Propane is an example of an exergonic reaction, but the reaction will only occur if there is an input of energy; a spark of energy that starts the reaction. -The energy barrier thus represents the amount of energy needed to start the reaction, known as the activation energy (Ea). -Transition-state intermediates have higher free energies than either the reactants or the products. Their bonds may be stretched and therefore unstable. Figure 8.8 Enzymes bind specific reactants at their active sites - Catalysts increase the rates of chemical reactions. Most nonbiological catalysts are nonspecific. In contrast, most biological catalysts are highly specific.
Figure 8.9 - In an enzyme-catalyzed reaction, the reactants are called substrates. Substrate molecules bind to a particular site on the enzyme, called the active site, where catalysis takes place. - The names of enzymes reflect their functions and often end with the suffix “ase.” - The binding of a substrate to the active site of an enzyme produces an enzyme–substrate complex (ES) that is held together by one or more means, such as hydrogen bonding, electrical attraction, or temporary covalent bonding. The enzyme–substrate complex gives rise to product and free enzyme: Enzyme + Substrate → ES → Enzyme + Product
11/28/16
What is the Enzymes lower the energy barrier but do not affect equilibrium relationship between -When reactants are bound to the enzyme, forming an enzyme–substrate complex, they require less an enzyme and the activation energy than the transition-state species of the corresponding uncatalyzed reaction. equilibrium point of a reaction?
Figure 8.10 -When an enzyme lowers the energy barrier, both the forward and the reverse reactions speed up, so the enzyme-catalyzed overall reaction proceeds toward equilibrium more rapidly than the uncatalyzed reaction. -Enzymes can change the rate of a reaction substantially. Summary:
A chemical reaction requires a “push” over the energy barrier to get started. The energy barrier is also known as the activation energy. Enzymes provide this activation energy by binding specific reactants (substrates). The reactants, or substrates, binds to the active site of the enzyme to produce an enzyme-substrate complex. This process lowers the energy barrier, but doesn’t affect the equilibrium of the reaction.