Energetics

1. Energetics Chapter 6 Adapted by G. Cornwall, Ph.D. From Raven’s Biology, McGraw Hill Publishing

2. Flow of Energy • Thermodynamics • Branch of chemistry concerned with energy changes • Cells are governed by the laws of physics and chemistry

3. Energy – capacity to do work • 2 states • Kinetic – energy of motion • Potential – stored energy • Many forms – mechanical, heat, sound, electric current, light, or radioactivity

4. Heat the most convenient way of measuring energy. • 1 calorie = heat required to raise 1 gram of water 1ºC • calorie or Calorie? • Energy flows into the biological world from the sun • Photosynthetic organisms capture this energy • Stored as potential energy in chemical bonds

5. Redox reactions • Oxidation • Atom or molecule loses an electron • Reduction • Atom or molecule gains an electron • Higher level of energy than oxidized form • Oxidation-reduction reactions (redox) • Reactions always paired

6. Laws of thermodynamics • First law of thermodynamics • Energy cannot be created or destroyed • Can only change from one form to another • Total amount of energy in the universe remains constant • During each conversion, some energy is lost as heat

7. Second law of thermodynamics • Entropy (disorder) is continuously increasing • Energy transformations proceed spontaneously to convert matter from a more ordered/ less stable form to a less ordered/ more stable form

8. Free energy • G = Energy available to do work • G = H – TS • H = enthalpy, energy in a molecule’s chemical bonds • T = absolute temperature • S = entropy, unavailable energy ΔG = ΔH - TS

9. ΔG = change in free energy • Positive ΔG • Products have more free energy than reactants • H is higher or S is lower • Not spontaneous, Requires input of energy • Endergonic • Neagtive ΔG • Products have less free energy than reactants • H is lower or S is higher or both • Spontaneous (may not be instantaneous) • Exergonic

10. Activation energy • Extra energy required to destabilize existing bonds and initiate a chemical reaction • Exergonic reaction’s rate depends on the activation energy required • Larger activation energy proceeds more slowly

11. Rate can be increased 2 ways • Increasing energy of reacting molecules (heating) • Lowering activation energy

12. Catalysts • Substances that influence chemical bonds in a way that lowers activation energy • Cannot violate laws of thermodynamics • Cannot make an endergonic reaction spontaneous • Do not alter the proportion of reactant turned into product

13. ATP • Adenosine triphosphate • Chief “currency” all cells use • Composed of • Ribose – 5 carbon sugar • Adenine • Chain of 3 phosphates • Key to energy storage • Bonds are unstable • ADP – 2 phosphates • AMP – 1 phosphate – lowest energy form

14. ATP cycle • ATP hydrolysis drives endergonic reactions • Coupled reaction results in net –ΔG (exergonic and spontaneous) • ATP not suitable for long term energy storage • Fats and carbohydrates better • Cells store only a few seconds worth of ATP

15. Card Quiz A Oxidation is the ____________ and reduction is the ________. • loss of electrons, gain of electrons • gain of protons, loss of protons • loss of protons, gain of protons • loss of electrons, gain of protons

16. Card Quiz A The first law of thermodynamics states that energy can be – • Created • Destroyed • Converted • Lost

17. Card Quiz A The energy in a system that is able to do work. • Enthalpy • Entropy • Free energy • Kinetic energy

18. Card Quiz A A reaction with a positive ∆G is – • Exergonic • Endergonic • Enthalpic • Energertic

19. Card Quiz A Spending ATP involves hydrolyzing it into ADP and inorganic P. The energy released can drive other chemical reactions. • This is true • This is false

20. Card Quiz A A catalyst speeds up chemical reactions. How do catalysts do this? • Decreasing entropy • Altering ∆G • Consuming reactants • Lowering activation energy

21. Card Quiz Answers • Green • Red • Red • Red • Green • Red

22. Enzymes • Most enzymes are protein • Some are RNA • Shape of enzyme stabilizes a temporary association between substrates • Enzyme not changed or consumed in reaction • Carbonic anhydrase • 200 molecules of carbonic acid per hour made without enzyme • 600,000 molecules formed per second with enzyme

23. Active site • Pockets or clefts for substrate binding • Forms enzyme-substare complex • Precise fit of substrate into active site • Applies stress to distort particular bond to lower activation energy • Induced fit

24. Enzymes may be suspended in the cytoplasm or attached to cell membranes and organelles • Multienzyme complexes – subunits work together to form molecular machine • Product can be delivered easily to next enzyme • Unwanted side reactions prevented • All reactions an be controlled as a unit

25. Nonprotein enzymes • Ribozymes • 1981 discovery that certain reactions catalyzed in cells by RNA molecule itself 2 kinds • Intramolecular catalysis – catalyze reaction on RNA molecule itself • Intermolecular catalysis – RNA acts on another molecule

26. Enzyme function • Rate of enzyme-catlyzed reaction depends on concentrations of substrate and enzyme • Any chemical or physical condition that affects the enzyme’s 3 dimensional shape can change rate • Optimum temperature • Optimum pH

27. Inhibitors • Inhibitor – substance that binds to enzyme and decreases its activity • Competitive inhibitor • Competes with substrate for active site

28. Noncompetitive inhibitor • Binds to enzyme at a site other than active site • Causes shape change that makes enzyme unable to bind substrate

29. Cofactors & Coenzymes • Cofactors: assist in enzyme function • Often metal ions found in active site • Zinc in corboxypeptidase • Required in the diet in small amounts • Coenzymes: a cofactor that is an organic molecule (non-protein) • Many are vitamins essential in our diets • Often coenzymes and cofactors are involved in capturing and transferring electrons

30. Allostery • Allosteric enzymes – enzymes exist in active and inactive forms • Most noncompetitive inhibitors bind to allosteric site – chemical on/off switch • Allosteric inhibitor – binds to allosteric site and reduces enzyme activity • Allosteric activator – binds to allosteric site and increases enzyme activity

31. Metabolism • Total of all chemical reactions carried out by an organism • Anabolic reactions / anabolism • Expend energy to build up molecules • Catabolic reactions/ catabolism • Harvest energy by breaking down molecules

32. Biochemical pathways • Reactions occur in a sequence • Product of one reaction is the substrate for the next • Many steps take place in organelles

33. Feedback inhibition • End-product of pathway binds to an allosteric site on enzyme that catalyses first reaction in pathway • Shuts down pathway so raw materials and energy are not wasted

34. Card Quiz B Small organic molecules that assist in enzymatic functions are – • Coprolites • Cofactors • Activators • Coenzymes

35. Card Quiz B Feedback inhibition occurs when the final product acts as an inhibitor to the first enzyme in the pathway. • This is true • This is false

36. Card Quiz B Carbon monoxide (CO) binds to the hemoglobin protein at the oxygen binding site. Once the CO binds, the oxygen can no longer be transported. What does this describe? • Non-competitive inhibition • Feedback inhibition • Allosteric inhibition • Competitive inhibition

37. Card Quiz B Increasing the temperature increases the rate of an enzyme-catalyzed reaction. Once a critical temperature is reached, the reaction stops. Why does this happen? • The concentration of reactants drop • The enzymes have all been consumed in the reaction • The increase in temperature alters the pH • The polypeptide chains in the enzyme denature

38. Card Quiz Answers • Yellow • Blue • Red • Red