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Metabolism

Metabolism. Campbell and Reece Chapter 8. Metabolism. total sum of all chemical reactions in an organism. Metabolic Pathways. begin with specific molecule which is altered in series of defined steps, resulting in certain product(s) each step has own specific enzyme

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Metabolism

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  1. Metabolism Campbell and Reece Chapter 8

  2. Metabolism • total sum of all chemical reactions in an organism

  3. Metabolic Pathways • begin with specific molecule which is altered in series of defined steps, resulting in certain product(s) • each step has own specific enzyme • mechanisms that regulate enzymes balance metabolic supply & demand

  4. Pathways can have >1 starting material &/or product)

  5. Catabolic Pathways • break down complex molecules into simpler one releasing nrg • example: cellular respiration

  6. Anabolic Pathways • build complex molecules out of simpler ones • require nrg • example: protein synthesis • nrg released from catabolic pathways used to fuel anabolic pathways

  7. Bioenergetics • study of how energy flows through living organisms

  8. Forms of Energy(capacity to do work) • KE • Thermal Energy • PE • Chemical Energy

  9. KE(energy of motion)

  10. Thermal Energy(heat) • KE ass’c with random movement of atoms or molecules

  11. Light Energy

  12. PE(energy matter possesses due to its position)

  13. Chemical Energy(type of PE) • in catabolic pathways

  14. Laws of Energy Transfer • thermodynamics: study of energy transfer that occurs in a system • system: matter being studied • surroundings: everything else in the universe • isolated or closed system: has no interaction with surroundings • open system: energy & matter can be transferred between system & surroundings

  15. 1st Law of Thermodynamics(Law of Conservation of Energy) • amt of energy in universe is constant • Energy can neither be created or destroyed

  16. 1st Law of Thermodynamics

  17. 2nd Law of Thermodynamics(Entropy) • in most nrg transfers, some nrg is lost to the system, usually in form of heat nrg • in case of digesting food, most of chemical nrg is lost as heat • logical consequence of losing nrg with each transfer: universe is becoming more disordered

  18. 2nd Law of Thermodynamics • entropy : a measure of the disorder or randomness of the universe • 2nd Law: every nrg transfer or transformation increases the entropy of the universe • (there is an unstoppable trend toward randomization of the universe)

  19. 2nd Law of Thermodynamics • spontaneous process: a process that can occur w/out input of energy • will always increase entropy of the universe

  20. Biologists use the Laws of Thermodynamics to predict which chemical reactions will happen spontaneously & which one require an input of nrg

  21. J. Willard Gibbs • Yale professor, 1878

  22. Gibbs Free-Energy (G) • is the part of a system’s nrg that can perform work when the T & P are uniform thru out the system (living cell fits this description)

  23. Gibbs Free Energy • system is the chemical reaction • enthalpy = total energy (in biologic systems) • ΔH = change in system’s enthalpy • ΔS = change in system’s entropy • absolute temperature (K) = ºC + 273

  24. Free-Energy Change (ΔG)ΔG = ΔH - TΔS • 0nce you know ΔG you can say whether a reaction will be spontaneous or require an input of nrg • *to be spontaneous ΔG must be (-) • for ΔG to be (-), either ΔH must be (-) (enthalpy decreases) or TΔS must be (+) (entropy increases)

  25. Spontaneous Reactions • all spontaneous reactions have a –ΔG which decreases the system’s free nrg • reactions with a (+) G or G = 0 are never spontaneous

  26. Another Way to Look at ΔG • ΔG = G (final state) + G(initial state) • because G(final state) has less free nrg it will be less likely to change thus the system will be more stable • think of free nrg as a measure of a system’s instability • unstable systems have higher G tend to change in such a way as to end with a more stable, lower G

  27. example Less Stable More Stable

  28. Equilibrium • state of maximum stability • as a chemical reaction moves toward equilibrium the free nrg of reactants & products gradually decreases • free nrg increases if reactants & products somehow pulled away from equilibrium (removing products from system)

  29. for a system @ equilibrium, G is @ its lowest possible value in that system • any change from that equilibrium position will have a (+) ΔG & so will not be spontaneous

  30. *because a system @ equilibrium cannot spontaneously change, it cannot do work • A process is spontaneous & can do work only when it is moving toward equilibrium.

  31. Free Energy & Metabolism • exergonic reaction: energy outward • proceeds with net release of free nrg • endergonic reaction: energy inward • proceeds only if absorption of free nrg • reversible chemical reactions must be endergonic in one direction & exergonic in the other direction

  32. Exergonic Reactions • reactions that occur spontaneously • ΔG is always (-) (reaction loses free nrg) • example: • 1M C6H12 O6 + 6 O2  6 CO2 + 6 H2O + 686 kcal (2,870 kJ)

  33. BREAKING BONDS OF REACTANTS DOES NOT RELEASE ENERGY… (IT REQUIRES ENERGY)

  34. ENDERGONIC REACTIONS • absorbs free energy from surroundings • G increases so can think of it as reaction that stores free energy • ΔG is always (+) (amount of G tells you how much energy needed to drive reaction) • nonspontaneous reactions

  35. Endergonic Reactions • example: • if cellular respiration of glucose yielded 686 kcal of energy then…. • plants had to add 686 kcal energy to make the glucose

  36. Equilibrium & Metabolism • reactions that have reached equilibrium cannot do work • chemical reactions of metabolism would reach equilibrium if they occurred in isolation (like in a test tube)

  37. If a cell reaches equilibrium it is dead!

  38. How do Cells Avoid Equilibrium? • products of reactions do not accumulate because they are used as reactants in the next reaction

  39. How do Cells Avoid Equilibrium? • Sequence of reactions keeps going because there is a large free-energy difference between the original reactant(s) and final product(s)

  40. Catabolic Pathways • energy released in “little packets” • if reaction simply started with original reactant(s ) final product(s) in a single step releasing all the energy at once would probably be catastrophic for the cell (and maybe the body)

  41. ATP Couples Exergonic Reactions with Endergonic Reactions

  42. 3 Kinds of Work Done by Cells • Chemical Work • Transport Work • Mechanical Work

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