Enzymatic Catalysis
• Enzymes do not affect equilibrium (Keq)...
• ...which means that enzymes cannot affect the free energy of the
reaction (ΔG°).
• Slow reactions face significant activation barriers (ΔG‡) that must be
overcome during the reaction.
• Enzymes increase reaction rates by decreasing the activation free
energy ΔG‡.
The energy required to form the transition state from the substrate is
called the activation energy, symbolized by ΔG‡
Rate Enhancement by selected Enzymes
Why Cells Need Enzymes?
• Under biologically relevant conditions, uncatalyzed reactions tend to
be slow.
• Most biological molecules are quite stable in neutral-pH, mild
temperature, aqueous environment inside cells.
, • Many common chemical processes are unfavorable or unlikely in
the cellular environment.
• Reactions required to digest food, send nerve signals, or contract
a muscle simply do not occur at a useful rate without catalysis.
Nomenclature of enzymes
• Adding the suffix “-ase” to the name of their substrate or to a word or
phrase describing their activity. e.g urease
• Early discovered enzymes were named for a broad function, before the
specific reaction catalyzed was known. e.g pepsin (from the Greek
pepsis, “digestion,”)
• Some early discovered enzymes were named for their source. e.g
trypsin (from Greek tryein, “to wear down,” since trypsin was obtained
by rubbing pancreatic tissue with glycerin)
• In some cases the same enzyme has two or more names, or two
different enzymes have the same name.
• Enzymes do not affect equilibrium (Keq)...
• ...which means that enzymes cannot affect the free energy of the
reaction (ΔG°).
• Slow reactions face significant activation barriers (ΔG‡) that must be
overcome during the reaction.
• Enzymes increase reaction rates by decreasing the activation free
energy ΔG‡.
The energy required to form the transition state from the substrate is
called the activation energy, symbolized by ΔG‡
Rate Enhancement by selected Enzymes
Why Cells Need Enzymes?
• Under biologically relevant conditions, uncatalyzed reactions tend to
be slow.
• Most biological molecules are quite stable in neutral-pH, mild
temperature, aqueous environment inside cells.
, • Many common chemical processes are unfavorable or unlikely in
the cellular environment.
• Reactions required to digest food, send nerve signals, or contract
a muscle simply do not occur at a useful rate without catalysis.
Nomenclature of enzymes
• Adding the suffix “-ase” to the name of their substrate or to a word or
phrase describing their activity. e.g urease
• Early discovered enzymes were named for a broad function, before the
specific reaction catalyzed was known. e.g pepsin (from the Greek
pepsis, “digestion,”)
• Some early discovered enzymes were named for their source. e.g
trypsin (from Greek tryein, “to wear down,” since trypsin was obtained
by rubbing pancreatic tissue with glycerin)
• In some cases the same enzyme has two or more names, or two
different enzymes have the same name.
