1 survey of biochemistry enzyme catalysis. 2 general properties of enzymes high reaction rates –10...
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SURVEY OF BIOCHEMISTRY
Enzyme Catalysis
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General Properties of Enzymes
• High reaction rates– 106 to 1012 times faster than uncatalyzed
reaction• Mild reaction conditions
– Temp < 100°C– Atmospheric Pressure– pH near 7
• High reaction specificity• Capacity for regulation
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Enzymes act on specific substrates
• Example of geometric specificity
Phenylalanine Tyrosine
TyrosineL-DOPA
(neurotransmitter)
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Classification of Enzymes
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Oxidoreductases
• Oxidoreductases catalyze redox reactions - those involving the transfer of electrons
M M+Oxidation
Loss of e-
XReduction
Gain of e-X-
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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 notdissociate from the enzyme
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Important Cofactors:NADH 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:
1. Positive2. Negative3. 04. ∆G does not relate to reaction
spontaneity
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PRS
• Which best describes heme?
1. Oxidoreductase2. Apoenzyme3. Prosthetic group4. 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