Energy and Metabolism Chapter 6

1. Energy and Metabolism Chapter 6 Topics you are not responsible for: How biochemical pathways evolve Read on your own about: Laws of thermodynamics End of Chapter questions: all Do all mQuiz questions Energy and Metabolism

2. How much “useable” energy exists in the molecules of a cell? G = H - TS G = usable energy (Gibbs free energy) Which equals … H = energy content in the molecular bonds (enthalpy)? … Less … S = disorder (entropy) x Temperature (Kelvin scale) Energy and Metabolism

3. What happens to the energy of a molecule during a chemical reaction? How does the energy content in the molecular bonds (enthalpy) change? ΔH How does the energy of disorder (entropy) change? ΔS (x Temperature) How does the total usable (‘Free’) energy (G) of the system change during the reaction? ΔG = ΔH– ΔST = -7 Kcal/mol “Catabolic”reaction “Exergonic” -- energy is released Energy and Metabolism

4. Catabolic (exergonic) reactions occur spontaneously… but often slowly. Why? What is activation energy? Energy and Metabolism

5. What happens if the reaction is reversed? Will ΔG (usable energy of the system) be increase or decrease? What happens to useable energy of the system? ΔG = ΔH– ΔST = +7 Kcal/mol Example of an Anabolic reaction (endergonic) -- energy must be added to the system Question Energy and Metabolism

6. How does an enzyme affect reaction energetics? How does it do so? “Catalytic site” Substrate orientation Enzyme movements Bond destabilization Question EPSP synthase binding to SP3 Catalysis Funke T et al. PNAS 2006;103:13010-13015 Energy and Metabolism

7. Enzyme reactions are reversible In a closed system. . . . . . will reach “equilibrium” -- what does this mean? -- Enzyme affinities Sucrase Activity Energy and Metabolism

8. In enzymatic reactions, energy can pass to or from ATP Glutamine synthase reaction Glutamate + NH3 + ATP  Glutamine + ADP + Pi Understand this if: Substrate +ATP  Product + ADP +Pi = endergonic / anabolic reaction if: Substrate +ADP+Pi  Product + ATP = exogonic / catabolic reaction Energy and Metabolism

9. Enzyme 1 Enzyme 2 Enzyme 3 What is a metabolic pathway? -- sequential series of enzymatic reactions -- e.g., Glycolysis, Krebs cycle, etc. Cellular “metabolism” = sum of all enzymatic activities Energy and Metabolism

10. If all enzymes are reversible, then why do molecules pass one way through metabolic pathways? What controls flow direction? 1) Reactant concentrations 2) Product removal Question Fig 6.13 in text is special case Energy and Metabolism

11. What controls the rate of enzyme activity? Various physical factors? pH Temperature Reactant & substrate concentrations Activators and Inhibitors Models Question Energy and Metabolism

12. Control of enzyme activity, con’t. Inhibitors competitive vs non-competitive Non-competitive = “allosteric regulation” Inhibitors Question Energy and Metabolism

13. What is feedback inhibition? Common regulatory mechanism Response to decreased demand for products

14. Understand this Substrate + NAD  Product + NADH = substrate oxidation Substrate + NADH  Product + NAD = substrate reduction In oxidation/reduction reactions, what serve as electron carrier? NADH, FADH, NADPH examples of “coenzymes” Lactate dehydrogenase Rx Question Energy and Metabolism