An Introduction to Metabolism

1. An Introduction to Metabolism A.P. Biology Chapter 8

2. Why do you eat?What is the purpose of a food chain? Answer: Energy and Organic Building Blocks

3. Bioenergetics • Bioenergetics- how energy behaves and changes in living systems (food chains). • Metabolism = Anabolism (require energy to make new bonds) + Catabolism (release energy from bonds)

4. Energy-The Stuff of Life! • Energy – the capacity to do work. • Two States of Energy: • Kinetic Energy- energy of motion. • Potential Energy- stored energy. Potential  Kinetic  Potential

5. Forms of energy? • Chemical • Mechanical • Electrical • Light • HEAT • Nuclear • Biology – potential chemical and kinetic chemical; light; heat (from chemical bonds)

6. Figure 8.1 • Some organisms • Convert chemical energy to light, as in bioluminescence

7. Measuring Energy in Biology • In terms of heat changes (thermodynamics). • Unit of heat in biology – calorie. • 1.0 calorie = amount of heat req’d to raise 1.0g of H20, 1° C. • In biology, 1.0 kilocalorie (kcal) = 1,000.0 calories (cal) • 1,000 cal = 1.0 kcal. = 1.0 Calorie

8. On the platform, a diver has more potential energy. Diving converts potential energy to kinetic energy. In the water, a diver has less potential energy. Climbing up converts kinetic energy of muscle movement to potential energy. Figure 8.2 • Energy can be converted from one form to another

9. Photosynthesis • Conversion of unusable light energy into usable chemical energy. C6H12O6

10. Redox Reactions

11. Photosynthesis Light 6 CO2 + 12 H2O  6 O2 + 6 H2O C6H12O6 Stores 686 kcal/mol

12. Photosynthesis is a Redox Reaction 6 CO2 + 12 H2O  6 O2 + 6 H2O C6H12O6 H

13. Cellular Respiration C6H12O6 + 6 O2 6 CO2 + 6 H2O + ENERGY (ATP) 686 kcal/mole glucose

14. Cellular Respiration is a Redox Reaction C6H12O6 + 6 O2 6 CO2 + 6 H2O + ENERGY (ATP) 686 kcal/mole glucose H

15. First Law of Thermodynamics • Energy cannot be created nor destroyed, but it can be converted from one form to another. • Ex. Food chains

16. Chemical energy (a) First law of thermodynamics: Energy can be transferred or transformed but Neither created nor destroyed. For example, the chemical (potential) energy in food will be converted to the kinetic energy of the cheetah’s movement in (b). Figure 8.3  An example of energy conversion

17. First Law of Thermodynamics Producers (Light Energy  Potential Chemical) 1st Order Consumer or Herbivore (Potential Chemical Potential, Kinetic Chemical) 2nd Order Consumer or Carnivore (Potential Chemical Potential, Kinetic Chemical) HEAT HEAT

18. Heat co2 + H2O (b Figure 8.3  The Second Law of Thermodynamics • According to the second law of thermodynamics • Spontaneous changes that do not require outside energy increase the entropy, or disorder, of the universe

19. 50µm Figure 8.4 Biological Order and Disorder • Living systems • Increase the entropy of the universe • Use energy to maintain order

20. 2nd Law of Thermodynamics • As energy is transformed from one state to another, some of the energy is lost as heat (random molecular motion) and the ability to do work decreases. • Disorder (Entropy) in the universe is increasing. • Order  Disorder

21. Free-Energy Change, G • A living system’s free energy • Is energy that can do work under cellular conditions

22. More free energy (higher G) • Less stable • Greater work capacity • In a spontaneous change • The free energy of the system decreases (∆G<0) • The system becomes more stable • The released free energy can • be harnessed to do work . • Less free energy (lower G) • More stable • Less work capacity (a) (c) (b) Gravitational motion. Objects move spontaneously from a higher altitude to a lower one. Diffusion. Molecules in a drop of dye diffuse until they are randomly dispersed. Chemical reaction. In a cell, a sugar molecule is broken down into simpler molecules. Figure 8.5  • At maximum stability • The system is at equilibrium

23. Chemical Bonds have Potential Energy • When bonds are broken, some of the energy is lost as heat and is not available to do work (form new chemical bonds). • Free Energy (G) – the amt. of energy in a bond available to do work. • In a molecule, the amt. of Free Energy (G) = the amt. of energy in chemical bond (Enthalpy, H) – the energy lost as disorder (Entropy, S). G = H - TS

24. Free Energy of Chemical Rxns. • ΔG = difference in bond energies between reactants and products of a chemical reaction. • Δ G = ΔH – TΔS • If ΔG is negative (products contain less energy than reactants) = Exergonic Reactions. Ex. Cellular Respiration • If ΔG ispositive (products contain more energy than reactants) = Endergonic Reactions. Ex. Photosynthesis

25. C6H12O6 + O2 HEAT Free Energy  G CO2 + H2O Cellular Respiration Rxn Time

26. C6H12O6 + O2 Light Energy Supplied Free Energy  G Photosynthesis CO2 + H2O Rxn Time

27. Reactants Amount of energy released (∆G <0) Free energy Energy Products Progress of the reaction (a) Exergonic reaction: energy released Figure 8.6 Exergonic and Endergonic Reactions in Metabolism • An exergonic reaction • Proceeds with a net release of free energy and is spontaneous

28. Products Amount of energy released (∆G>0) Free energy Energy Reactants Progress of the reaction Figure 8.6 (b) Endergonic reaction: energy required An endergonic reaction: • Is one that absorbs free energy from its surroundings and is nonspontaneous

29. ∆G < 0 ∆G = 0 (a) A closed hydroelectric system. Water flowing downhill turns a turbine that drives a generator providing electricity to a light bulb, but only until the system reaches equilibrium. Figure 8.7 A Equilibrium and Metabolism • Reactions in a closed system • Eventually reach equilibrium

30. ∆G < 0 (b) An open hydroelectric system. Flowing water keeps driving the generator because intake and outflow of water keep the system from reaching equlibrium. Figure 8.7 • Cells in our body • Experience a constant flow of materials in and out, preventing metabolic pathways from reaching equilibrium

31. ∆G < 0 ∆G < 0 ∆G < 0 (c) A multistep open hydroelectric system. Cellular respiration is analogous to this system: Glucoce is brocken down in a series of exergonic reactions that power the work of the cell. The product of each reaction becomes the reactant for the next, so no reaction reaches equilibrium. Figure 8.7 An analogy for cellular respiration

32. Concept 8.3: ATP powers cellular work by coupling exergonic reactions to endergonic reactions • A cell does three main kinds of work: • Mechanical • Transport • Chemical • Energy coupling • Is a key feature in the way cells manage their energy resources to do this work

33. Adenine NH2 C N C N HC O O O CH C N - N O O O O CH2 O - - - O O O H H Phosphate groups H Ribose H Figure 8.8 OH OH The Structure and Hydrolysis of ATP • ATP (adenosine triphosphate) • Is the cell’s energy shuttle • Provides energy for cellular functions

34. P P P Adenosine triphosphate (ATP) H2O + Energy P i P P Adenosine diphosphate (ADP) Inorganic phosphate Figure 8.9 • Energy is released from ATP • When the terminal phosphate bond is broken

35. Endergonic reaction: ∆G is positive, reaction is not spontaneous NH2 NH3 + ∆G = +3.4 kcal/mol Glu Glu Glutamic acid Glutamine Ammonia Exergonic reaction: ∆ G is negative, reaction is spontaneous ∆G = + 7.3 kcal/mol + P ADP H2O ATP + Coupled reactions: Overall ∆G is negative; together, reactions are spontaneous ∆G = –3.9 kcal/mol Figure 8.10 ATP hydrolysis: Can be coupled to other reactions

36. How ATP Performs Work • ATP drives endergonic reactions: • By phosphorylation, transferring a phosphate to other molecules

37. P i P Motor protein Protein moved (a) Mechanical work: ATP phosphorylates motor proteins Membrane protein ADP + ATP P i P P i Solute Solute transported (b) Transport work: ATP phosphorylates transport proteins P NH2 + + NH3 P i Glu Glu Reactants: Glutamic acid and ammonia Product (glutamine) made Figure 8.11 (c) Chemical work: ATP phosphorylates key reactants The three types of cellular work • Are powered by the hydrolysis of ATP

38. ATP hydrolysis to ADP + P i yields energy ATP synthesis from ADP + P i requires energy ATP Energy from catabolism (exergonic, energy yielding processes) Energy for cellular work (endergonic, energy- consuming processes) ADP + P i Figure 8.12 The Regeneration of ATP • Catabolic pathways • Drive the regeneration of ATP from ADP and phosphate