1. CHAPTER 6 Energy and Metabolism 1

2. 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 1.Kinetic – energy of motion 2.Potential – stored energy –Many forms – mechanical, heat, sound, electric current, light, or radioactivity –Heat the most convenient way of measuring energy 3

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5. Energy flows into the biological world from the sun Photosynthetic organisms capture this energy Stored as potential energy in chemical bonds 5

6. 6 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

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8. 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 8

9. 9 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

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12. 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 Rate can be increased 2 ways 1.Increasing energy of reacting molecules (heating) 2.Lowering activation energy 12

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14. Catalysts Substances that influence chemical bonds in a way that lowers activation energy Cannot violate laws of thermodynamics Do not alter the proportion of reactant turned into product 14

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16. 16 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

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18. 18 ATP cycle ATP hydrolysis drives endergonic reactions –ATP hydrolysis is an exergonic reaction ATP not suitable for long term energy storage –Cells store only a few seconds worth of ATP

19. The triphosphate tail of ATP is unstable. The bonds between the phosphate groups can be broken by hydrolysis releasing chemical energy (EXERGONIC); A molecule of inorganic phosphate (P i ) and ADP are the products of this RXN: ATP --------------> Adenosine Diphosphate (ADP) + P i ; The inorganic phosphate from ATP can now be transferred to some other molecule which is now said to be "phosphorylated"; ADP can be regenerated to ATP by the addition of a phosphate in a endergonic RXN; Adenosine Diphosphate (ADP) + P i --------------> ATP 19

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21. 21 Enzymes Most enzymes are protein Shape of enzyme stabilizes a temporary association between substrates Enzyme not changed or consumed in reaction

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23. Active site Pockets or clefts for substrate binding Precise fit of substrate into active site Location - Enzymes may be suspended in the cytoplasm or attached to cell membranes and organelles 23

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26. Enzyme function Rate of enzyme-catalyzed 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 26

27. The cellular environment affects enzyme activity. A. Factors such as temperature, pH, salt concentration, and the presence of cofactors often affect the way enzymes work. Recall- denaturation B. The active site of an enzyme may not always be exposed (recall the 3-dimentional conformation of proteins), and a cofactor or coenzyme may be necessary to "activate" the enzyme so it can react with its substrate. a. Cofactor = an ion of a metal (mineral like Fe ++, Cu ++, Zn ++ ). b. Coenzyme = vitamin (primarily B vitamins). 27

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29. 29 Inhibitors Inhibitor – substance that binds to enzyme and decreases its activity Competitive inhibitor –Competes with substrate for active site Noncompetitive inhibitor –Binds to enzyme at a site other than active site –Causes shape change that makes enzyme unable to bind substrate

30. Many poisons, pesticides, and drugs are enzyme inhibitors. A.For example, cyanide inhibits the production of ATP during respiration and the nerve gas sarin inhibits the enzyme acetylcholinesterase. B.The pesticide malathion also inhibits the enzyme acetylcholinesterase but is used at doses too low to be harmful to humans. C.The antibiotic penicillin interferes with an enzyme that helps build bacterial cell walls. D.Pain killers such as aspirin and ibuprofen inhibit the enzyme used to induce pain. Other therapeutic drugs used to combat HIV and cancer are also enzyme inhibitors. 30

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32. 32 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

33. 33 Biochemical pathways Reactions occur in a sequence Product of one reaction is the substrate for the next Many steps take place in organelles

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