Introduction to Metabolism

1. Introduction to Metabolism

2. I. The Flow of Energy A. Laws of Thermodynamics 1. First Law -energy can be transferred or transformed, but not created or destroyed

3. I. The Flow of Energy A. Laws of Thermodynamics 2. Second Law -predicts the direction of all energy exchanges -every energy change increases the Entropy of the universe OR -in every energy change, potential energy decreases

4. I. The Flow of Energy A. Laws of Thermodynamics 2. Second Law a. Organisms and the Second Law -Living things are Ordered but the Universe is increasing in Disorder? 1) Open System vs Closed Systems -Open: energy/matter exchanged with surroundings -Closed: isolated from surroundings (Universe) 2) Organisms are Open Systems -take in ordered energy; release disordered -increasing Entropy => second law

5. I. The Flow of Energy B. Spontaneous Change/Reactions and Free Energy 1. Spontaneous Change/Reaction -occurs without outside help a. Reactants -unstable/ordered (low entropy) -high energy b. Products -stable/disordered (high entropy) -less energy (exergonic)

6. I. The Flow of Energy B. Spontaneous Change/Reactions and Free Energy 2. Free Energy – energy available to do work -indicator of spontaneous change/reactions -involves changes in heat and entropy ΔG = ΔH - TΔS - ΔG < 0 in spontaneous change

7. I. The Flow of Energy B. Spontaneous Change/Reactions and Free Energy 3. Free Energy and Equilibrium -reactions are reversible a. Equilibrium -products = reactants -“Energy Valley” - ΔG = 0

8. I. The Flow of Energy B. Spontaneous Change/Reactions and Free Energy 4. Free Energy and Metabolism a. Exergonic Reactions -free energy released -spontaneous -cell respiration b. Endergonic Reactions -free energy is absorbed -nonspontaneous -photosynthesis

9. I. The Flow of Energy B. Spontaneous Change/Reactions and Free Energy 4. Free Energy and Metabolism c. Metabolic Disequilibrium -Cell at equilibrium (ΔG = 0) = Death -Cells maintain Disequilibrium -Open Systems -Energy Flows in and out

10. II. Metabolism -sum of all chemical reactions occurring in living systems A. Metabolic Pathways -groups of ordered reactions 1. Catabolic Pathways -breakdown substances -release free energy(Exergonic) -cell respiration 2. Anabolic Pathways -synthesis -photo, protein synthesis -free energy absorbed (Endergonic)

11. III. ATP (Adenosine Triphosphate) -“energy currency” A. Structure -similar to RNA Nucleotide -Adenine plus 2 phosphate groups

12. III. ATP (Adenosine Triphosphate) -“energy currency” B. Hydrolysis of ATP -terminal phosphate bond broken => energy released -ATP => ADP + Pi + Energy - ΔG = -13kcal/mole

13. III. ATP (Adenosine Triphosphate) -“energy currency” C. Energy Coupling by ATP -ATP couples Exergonic process to a Endergonic process 1. Phosphorylation -hydrolysis of ATP; enzymes transfer P group to another molecule => “Phosphorylated Intermediate” -less stable -more free energy -molecule can now do work

16. III. ATP (Adenosine Triphosphate) -“energy currency” D. The ATP Cycle – Regeneration of ATP - ADP is phosphorylated => ATP - hydrolysis of ATP => ADP + Pi + Energy

17. IV. Enzymes A. Characteristics -catalysts – speed up reactions without being used up -globular proteins

18. IV. Enzymes B. Free Energy of Activation -reactions require breaking of bonds in reactants -absorb energy (usually heat) from surroundings; makes bonds unstable 1. Activation Energy (EA) -energy needed to break bonds in reactants; start reaction -makes bonds unstable => Transition State -inc. Free Energy of reactants

19. IV. Enzymes B. Free Energy of Activation 2. Significance of the Activation Energy Barrier -prevents cellular molecules from breaking down spontaneously -typical cell temps prevent reaching transition state (barrier) -However, EA barrier must be overcome for reactions to take place -Heat will cause denaturing – damage cells -Enzymes lower EA w/out raising temps. -Do Not affect ΔG

20. IV. Enzymes C. Enzyme Functioning 1. Substrate Specific -due to shape of active site 2. Induced Fit Model -substrate enters active site – weakly bonds -bonding causes enzyme to “clasp” around substrate

21. IV. Enzymes D. Effect of pH and Temperature 1. Temp affects molecular motion -high temps denature enzyme -30oC -40oC in humans 2. pH -optimum for different enzymes

22. IV. Enzymes E. Cofactors -nonprotein “helpers” -may bind to active site or to substrate -many are inorganic (zinc, Fe, Cu) -Coenzymes: organic cofactors -vitamins

23. IV. Enzymes F. Enzyme Inhibitors -reversible (weak bonds) or irreversible (covalent) 1. Competitive Inhibitors -compete with substrate for active site -reverisble -overcome by increasing conc. of substrate 2. Noncompetitive Inhibitors -bind to location other than active site -changes shape of active site -ex. DDT, penicillin

24. V. Control of Metabolism -control of enzyme activity and location A. Allosteric Regulation 1. Allosteric Sites -receptor site on enzyme for binding of regulatory molecules -binding may inhibit or stimulate enzyme

25. V. Control of Metabolism -control of enzyme activity and location A. Allosteric Regulation 2. Allosteric Enzymes -two or more polypeptides => enzyme complex -oscillates between active and inactive forms a. Allosteric Activator -stabilizes active form b. Allosteric Inhibitor -stabilizes inactive form

26. V. Control of Metabolism B. Feedback Inhibition -switching off of metabolic pathway by its end product -end product acts as inhibitor somewhere in pathway

28. V. Control of Metabolism C. Cooperativity -similar to allosteric enzymes -enzymes with multiple active sites -binding of substrate in one active site makes functional allothers