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
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
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
The enzyme changes sh