Transcript SURVEY OF BIOCHEMISTRY - School of Chemistry and …

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
Tyrosine
L-DOPA
(neurotransmitter)
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Classification of Enzymes
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Oxidoreductases
• Oxidoreductases catalyze redox
reactions - those involving the transfer
of electrons
Oxidation
M
X
Loss of
e-
Reduction
Gain of e-
M+
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 wellformed, 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 Cofactors:
NADH and NADPH
Examples of
cosubstrates
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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.
2.
3.
4.
Positive
Negative
0
∆G does not relate to reaction
spontaneity
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PRS
• Which best describes heme?
1.
2.
3.
4.
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
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