An Introduction to Metabolism

1. An Introduction to Metabolism A.P. Biology

4. Figure 8.1 The living cell Is a miniature factory where thousands of reactions occur • Converts energy in many ways Bioluminescence

5. Metabolism • Is the totality of an organism’s chemical reactions • Arises from interactions between molecules • An organism’s metabolism transforms matter and energy, subject to the laws of thermodynamics

6. Thermodynamics • Is the study of energy transformations • The first law of thermodynamics • Energy can be transferred and transformed • Energy cannot be created or destroyed • The second law of thermodynamics • Spontaneous changes that do not require outside energy increase the entropy, or disorder, of the universe

7. 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  1st Law of Thermodynamics

8. Heat co2 + H2O Second law of thermodynamics: Every energy transfer or transformation increases the disorder (entropy) of the universe. For example, disorder is added to the cheetah’s surroundings in the form of heat and the small molecules that are the by-products of metabolism. (b) Figure 8.3  2nd Law of Thermodynamics

10. Living systems • Increase the entropy of the universe • Use energy to maintain order

11. Enzyme 1 Enzyme 2 Enzyme 3 A D C B Reaction 1 Reaction 2 Reaction 3 Startingmolecule Product Metabolic Pathways • A metabolic pathway has many steps • That begin with a specific molecule and end with a product • That are each catalyzed by a specific enzyme

12. Types of Metabolic Pathways • Catabolic pathways • Break down complex molecules into simpler compounds • Release energy • Anabolic pathways • Build complicated molecules from simpler ones • Consume energy

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

15. Free Energy • Free energy measures the portion of a system’s energy that can perform work when the temperature & pressure are uniform throughout the system. (like in cells) • The free-energy change of a reaction tells us whether the reaction occurs spontaneously • A living system’s free energy • Is energy that can do work under cellular conditions

19. Change in free energy, ∆G • The change in free energy, ∆Gduring a biological process • Is related directly to the enthalpy change (∆H) and the change in entropy • ∆G = ∆H – T∆S T = Absolute temp in Kelvin (K)

20. ∆G • The value of ∆ G for a reaction at any moment in time tells us two things. • The sign of ∆ G tells us in what direction the reaction has to shift to reach equilibrium. • The magnitude of ∆ G tells us how far the reaction is from equilibrium at that moment.

21. More free energy (higher G) • Less stable • Greater work capacity • In a spontaneously 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 Gravitational motion. Objects move spontaneously from a higher altitude to a lower one. Chemical reaction. In a cell, a sugar molecule is broken down into simpler molecules. (a) (c) (b) Diffusion. Molecules in a drop of dye diffuse until they are randomly dispersed. Figure 8.5  • At maximum stability • The system is at equilibrium

22. Free Energy • During a spontaneous change • Free energy decreases and the stability of a system increases • For a spontaneous reaction to occur: • Loss of enthalpy (Heat) -or- • Loss of order (Gain in entropy) -or both

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

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

27. ∆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 Reactions in a closed system • Eventually reach equilibrium

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

29. ∆G < 0 ∆G < 0 ∆G < 0 (c) A multi-step open hydroelectric system. Cellular respiration is analogous to this system: Glucose is broken 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

30. ATP – Adenosine Tri-phosphate • ATP powers cellular work by coupling exergonic reactions to endergonic reactions • A cell does three main kinds of work • Mechanical • Transport • Chemical

31. 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 H Ribose Figure 8.8 OH OH The Structure and Hydrolysis of ATP • Provides energy for cellular functions

32. P P P Adenosine triphosphate (ATP) H2O Energy + P i P P Adenosine diphosphate (ADP) Inorganic phosphate Figure 8.9 Energy is released from ATPWhen the terminal phosphate bond is brokenand the negative charge on the PO4 groups repel

34. Endergonic reaction: ∆G is positive, reaction is not spontaneous NH2 NH3 + ∆G = +3.4 kcal/mol Glu Glu Glutamine Glutamic acid 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 hydrolysiscan be coupled to other reactions ATP hydrolysis

35. 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 ATP drives endergonic reactionsBy phosphorylation, transferring a phosphate to other molecules Three types of cellular work are powered by the hydrolysis of ATP

36. 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

37. ∆ G = +7.3 kcal/mol ∆ G = -7.3 kcal/mol

38. Enzymes • Enzymes speed up metabolic reactions by lowering energy barriers • A catalyst • Is a chemical agent that speeds up a reaction without being consumed by the reaction • An enzyme • Is a catalytic protein E + S  ES  E + P

40. CH2OH CH2OH CH2OH CH2OH O O O O H H H H H H H Sucrase H OH H HO OH H HO H2O O + H H OH O HO CH2OH CH2OH OH H H H OH H OH OH Fructose Glucose Sucrose Figure 8.13 C12H22O11 C6H12O6 C6H12O6 Every chemical reaction between moleculesInvolves both bond breaking and bond forming • Hydrolysis is an example of a chemical reaction

41. Activation Energy (EA) • The activation energy, EA • Is the initial amount of energy needed to start a chemical reaction • Is often supplied in the form of heat from the surroundings in a system • An enzyme catalyzes reactions • By lowering the EA barrier

43. A B D C Transition state B A EA D C Free energy Reactants B A ∆G < O C D Products Progress of the reaction Figure 8.14 Exergonic Reactions

44. Course of reaction without enzyme EA without enzyme EA with enzyme is lower Reactants Free energy ∆G is unaffected by enzyme Course of reaction with enzyme Products Progress of the reaction Figure 8.15

45. Substrate Active site Enzyme Figure 8.16 (a) Substrate Specificity of Enzymes • The substrate • Is the reactant an enzyme acts on • The enzyme • Binds to its substrate, forming an enzyme-substrate complex • The active site • Is the region on the enzyme where the substrate binds

46. Enzyme- substrate complex (b) Figure 8.16 Induced fit of a substrate • Brings chemical groups of the active site into positions that enhance their ability to catalyze the chemical reaction

47. Enzyme & Substrate fit like a lock & key (Shape specific) pH or temperature can change the active site shape on any enzyme Active site is where the reactants bind to the enzyme

48. 1 Substrates enter active site; enzyme changes shape so its active site embraces the substrates (induced fit). 2 Substrates held in active site by weak interactions, such as hydrogen bonds and ionic bonds. 3 Active site (and R groups of its amino acids) can lower EA and speed up a reaction by • acting as a template for substrate orientation, • stressing the substrates and stabilizing the transition state, • providing a favorable microenvironment, • participating directly in the catalytic reaction. Substrates Enzyme-substrate complex 6 Active site Is available for two new substrate Mole. Enzyme 5 Products are Released. 4 Substrates are Converted into Products. Figure 8.17 Products

49. The active site can lower an EA barrier by: • Orienting substrates correctly • Straining substrate bonds • Providing a favorable microenvironment • Covalently bonding to the substrate

50. Optimal temperature for typical human enzyme Optimal temperature for enzyme of thermophilic (heat-tolerant) bacteria Rate of reaction 80 0 20 100 40 Temperature (Cº) (a) Optimal temperature for two enzymes Figure 8.18 The activity of an enzyme • Is affected by general environmental factors • Temperature • pH