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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