SURVEY OF BIOCHEMISTRY Enzyme Catalysis

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SURVEY OF BIOCHEMISTRYEnzyme Catalysis
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General Properties of Enzymes

• High reaction rates
• 106 to 1012 times faster than uncatalyzed
  reaction
• Mild reaction conditions
• Temp lt 100C
• Atmospheric Pressure
• pH near 7
• High reaction specificity
• Capacity for regulation

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Enzymes act on specific substrates

• Example of geometric specificity

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Classification of Enzymes
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Oxidoreductases

• Oxidoreductases catalyze redox reactions - those
  involving the transfer of electrons

Oxidation
M
M
Loss of e-
X-
Reduction
X
Gain of e-
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Oxidoreductases
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Transferases

• Transferases catalyze the transfer of a specific
  group from one molecule to another.

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Hydrolases

• Hydrolases break down chemicals through the use
  of water.

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Lyases

• Cleave C-C, C-O, C-N, and other bonds by
  elimination, leaving double bonds or rings

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Isomerases

• Catalyze geometric or structural changes within a
  molecule

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Ligases

• Catalyze the joining of 2 molecules coupled with
  the hydrolysis of ATP or some similar
  triphosphate.

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Enzyme bind substrates
Binding of E to S usually involves noncovalent
interactions Binding pocket is well-formed, but
induced fitting can occur Substrate or inhibitor
binding is usually based on complementarity
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Types of Cofactors
Holoenzyme protein its cofactor Apoenzyme
protein without its cofactor Prosthetic group
tightly bound cofactor that does
not dissociate from the enzyme
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Important CofactorsNADH and NADPH
Examples ofcosubstrates
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Thermodynamics Energy for Reaction Chemistry
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Thermodynamics Energy for Reaction Chemistry
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PRS
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PRS

• A chemical reaction can occur spontaneously if ?G
  is
• Positive
• Negative
• 0
• ?G does not relate to reaction spontaneity

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PRS

• Which best describes heme?
• Oxidoreductase
• Apoenzyme
• Prosthetic group
• Holoenzyme

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Reminders

• No office hours today - Mon, Jun 9
• Exams to be returned on Wed
• Read Chapter 11
• Practice drawing structures
• All 20 amino acids
• All 5 nucleotides (A, T, G, C, U)
• NADH and NADPH