生命的化學工業：化學反應與酵素

1. 生命的化學工業：化學反應與酵素 10-12-2015

2. 生物有別於非生物的特點 能量的吸收與利用 –結構的維持與更新 Life can only occur in an open system with continuous flux of energy andmaterial.

3. Thermodynamics • First law: energy is conserved.

4. 不能利用的動能轉變成可以利用的位能

5. 能量：生命運作的動力 能量的轉變

6. Energy transformation Make all living organisms on earth alive!

7. 食物分子中生命不能利用的化學能,經由細胞的代謝反應轉變成生命可以利用的化學能食物分子中生命不能利用的化學能,經由細胞的代謝反應轉變成生命可以利用的化學能

8. Metabolic Pathways

9. How to judge whether one chemical reaction will spontaneously occur or not?

10. But how to express it?  The road to equilibrium is down the free energy hill!

13. 自由能的大小决定化學反應的方向及容易的程度！自由能的大小决定化學反應的方向及容易的程度！

14. Some remarks on the Gibbs free energy • It's not necessarily "free“ • ΔG is the maximum amount of energy which can be “freed” from the system to perform useful work. • It's not energy! • it is not conserved. • It's not even "real"! • it has no physical reality as a property of matter • it is simply a useful construct that serves as a criterion for change and makes calculations easier

15. Gibb’s free energy is a state function that expresses the spontaneity of a chemical reaction in terms of enthalpy and entropy change of the system.

18. Thermodynamic aspect of chemical reaction Does the reaction occur? At which direction? Proceed to what extend? Enthalpy and equilibrium constant But it will not tell us how fast of the reaction!

19. Kenetic aspect of chemical reaction How fast (rate) of the reaction occur? Zero, first and second order kinetics

20. Hydrogen + Oxygen = Water + heat Explosion! 放熱反應：△G 為負值，反應能自動進行!

21. Hydrogen + Oxygen = Water + heat Will it happen? Never at room temperature! Why? You need match!

22. Hydrogen + Oxygen = Water + heat Match provides a little bite of energy (activation energy) to break the chemical bond between two hydrogen and oxygen atoms. Then the oxygen and hydrogen atom join to form a new (stronger) chemical bond. More energy will be released as heat to the environment. The total energy balance is positive. Do we have such reaction in our body? Can or how we utilize the heat released from this reaction?

23. hydrogen hydrogen

26. How to make a chemical reaction occurring faster? (活化能) 自由能 To keep temperature high; to put high pressure or to increase concentration of the reactants; or To reduce activation energy by catalyst

27. Catalyst can only accelerate reaction rate, but would not change the net energy balance or equilibriumof the chemical reaction. Every chemical reaction in living system needs catalyst to make reaction occurring possibleat room temperature and pressure!

28. The catalyst in living system is “enzyme”. Most of enzymes are made of protein.

29. 生命運作的主角 : 蛋白質To make chemical reaction (synthesis and degradation) occur in the cell

32. 04_09_Proteins.jpg

33. Enzyme binds specific molecules: substrate! Just like lock and key ?

34. Yes and No! 04_31_specific ligands.jpg

36. Hexokinase Undergoes Induced Fit on Substrate Binding

37. The rate accelerations caused by five different enzymes

38. How does enzyme accelerates reaction rate?

42. Turnover number of enzyme:一個enzyme分子每秒可以轉變幾個分子的 substrate into products.

43. Ribozyme: RNA can be an enzyme (catalysis) Why RNA but not DNA has catalytic power?

44. How enzyme activity can be regulated? • Amount of enzyme protein (gene expression) • Transcriptional rate • Stability of mRNA • Translational rate • Stability of protein • Post translational modification • Cleavage of proenzyme into active enzyme • Chemical modification such as phosphorylation • Environmental factors • Temperature, pH, inhibitors, activators etc.

46. Which amino acid may participate in pepsin’s catalysis?

48. Allosteric inhibitor or activator shares similar working mechanism.

50. Synthesize C, U and T 04_39_conform.change.jpg