1 SURVEY OF BIOCHEMISTRY Enzyme Catalysis

2 General Properties of Enzymes High reaction rates –10 6 to times faster than uncatalyzed reaction Mild reaction conditions –Temp < 100°C –Atmospheric Pressure –pH near 7 High reaction specificity Capacity for regulation

3 Enzymes act on specific substrates Example of geometric specificity Phenylalanine Tyrosine L-DOPA (neurotransmitter)

4 Classification of Enzymes

5 Oxidoreductases Oxidoreductases catalyze redox reactions - those involving the transfer of electrons M M+M+ Oxidation Loss of e - X Reduction Gain of e - X-X-

6 Oxidoreductases

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

8 Hydrolases Hydrolases break down chemicals through the use of water.

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

10 Isomerases Catalyze geometric or structural changes within a molecule

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

12 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

13 Types of Cofactors Holoenzyme: protein + its cofactor Apoenzyme: protein without its cofactor Prosthetic group: tightly bound cofactor that does not dissociate from the enzyme

14 Important Cofactors: NADH and NADPH Examples of cosubstrates

15 Thermodynamics: Energy for Reaction Chemistry

16 Thermodynamics: Energy for Reaction Chemistry

17 PRS

18 PRS A chemical reaction can occur spontaneously if ∆G is: 1.Positive 2.Negative ∆G does not relate to reaction spontaneity

19 PRS Which best describes heme? 1.Oxidoreductase 2.Apoenzyme 3.Prosthetic group 4.Holoenzyme

20 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