Lecture 6.docx

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Biology - Biological Sciences
BSC 2010

Lecture 6 Concept 3.3 Some Proteins Act as Enzymes to Speed up Biochemical Reactions  Enzymes may use one or more mechanisms to catalyze a reaction: o Inducing Strain—bonds in the substrate are stretched, putting it in an unstable transition state. o Are Substrate orientation —substrates are brought together so that bonds can form. o —R groups may be directly involved in the reaction.  Maximum rate is used to calculate enzyme efficiency—molecules of substrate converted to product per unit time (turnover). o It ranges from 1 to 40 million molecules per second! Concept 3.4 Regulation of Metabolism Occurs by Regulation of Enzymes  Enzyme catalyzed reactions are part of metabolic pathways- the product of one reaction is a substrate for the next.  Homeostasis- the maintenance of stable internal conditions  Cells can regulate metabolism by controlling the amount of an enzyme.  Cells often have the ability to turn synthesis of enzymes off or on.  Chemical inhibitors can bind to enzymes and slow reaction rates.  Natural inhibitors regulate metabolism; artificial inhibitors are used to treat diseases, kill pests, and study enzyme function.  Irreversible inhibition—inhibitor covalently binds to a side chain in the active site. The enzyme is permanently inactivated.  Reversible inhibition (more common in cells): o A competitive inhibitor competes with natural substrate for active site. o A noncompetitive inhibitor binds at a site distinct from the active site—this causes change in enzyme shape and function.  Allosteric regulation-non-substrate molecule binds a site other than the active site (the allosteric site)  The enzyme changes sh
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