1. CHAPTER 6 Energy, Enzymes, and Metabolism

2. Energy and Energy Conversions
Energy is the capacity to do work
Potential energy is the energy of state or position; it includes energy stored in chemical bonds
Kinetic energy is the energy of motion
Potential energy can be converted to kinetic energy, which does work.

3. Energy Conversion
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Kinetic
Potential

4. First Law of Thermodynamics
Energy cannot be created or destroyed.

5. Second Law of Thermodynamics
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In a closed system, the quantity of energy available to do work decreases and unusable energy increases
Usable energy = free energy (G)
Unusable energy = product of entropy (S) and absolute temperature (T)
Total energy before transformation = enthalpy (H)

6. Energy and Energy Conversions
Organisms are open systems that are part of a larger closed system (universe)

7. Energy and Energy Conversions
Changes in free energy, total energy, temperature, and entropy are related
DG = DH – TDS
Exergonic reactions
Release free energy
Have a negative DG
Entropy increases, enthalpy decreases
Spontaneous
Endergonic reactions
Take up free energy
Have a positive DG
Entropy decreases, enthalpy increases
Non-spontaneous

8. Reactions
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9. Energy and Energy Conversions
G determines equilibrium point
Exergonic reactions
Equilibrium lies toward completion
Endergonic reacitons
Reaction will not occur without input of energy
G-1-P  G-6-P G=-1.7kcal/mol

10. ATP: Transferring Energy in Cells
ATP - an energy currency in cells
Hydrolysis of ATP releases free energy.

11. ATP: Transferring Energy in Cells
Reaction Coupling
couples exergonic and endergonic reactions

12. Coupling Reaction
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Glutamate

13. Enzymes: Biological Catalysts
Rates of reactions are independent of DG
Determined by the activation energy
Catalysts speed reactions by lowering the activation energy

14. Enzymes: Biological Catalysts
Highly specific for their substrates
Active site
determines specificity
where catalysis takes place
enzyme–substrate complex
Domains

15. Enzymes: Biological Catalysts
In the active site, the substrate is induced into a transition state
Transition state
temporary substrate configuration
Inducing & stabilizing the transition state decreases activation energy & increases reaction rate

16. Catalytic Mechanisms
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Lysozyme

17. Molecular Structure Determines Enzyme Function
Induced Fit
Enzyme conformation alters upon substrate binding

18. Enzymes: Biological Catalysts
Substrate concentration affects the rate of an enzyme-catalyzed reaction

19. Molecular Structure Determines Enzyme Function
The active sites of many enzymes contain special reactive molecules which mediate the chemical catalysis

20. Metabolism and Enzyme Regulation
Metabolic pathways
Upstream downstream sequence of reactions
Product of one reaction is a reactant for the next
Regulation of enzymes
Feedback inhibition
Downstream products inhibit upstream enzymes

21. Enzyme Regulation - Competitive Inhibition
Succinate  fumarate  malate  OAA
Build up of OAA inhibits succinate dehydrogenase

22. Enzyme Regulation - Competitive Inhibition
Thr  a-Ketobutyrate   Ile
Buildup of Ile inhibits threonine dehydratase

23. Enzyme Regulation - Suicide Inhibitors
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Inhibitor reacts with amino acids in the active site permanently inhibiting the enzyme
PMSF inhibits serine proteases such as trypsin

24. Metabolism and Enzyme Regulation
Allosteric enzymes,
reaction rate v substrate concentration is sigmoidal

25. Enzyme Regulation
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Allosteric inhibitors bind to sites different from the active site
Multiple catalytic subunits may interact cooperatively

26. Enzyme Regulation
End product of pathway may inhibit upstream allosteric enzymes

27. Enzyme Regulation
pH and temperature affect enzyme activity