Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. CHAPTER 6 LECTURE SLIDES To run the animations you must be in Slideshow View. Use the buttons on the animation to play, pause, and turn audio/text on or off. Please note: once you have used any of the animation functions (such as Play or Pause), you must first click in the white background before you advance the next slide.

Energy and Metabolism SWBAT: Explain enzyme function by their lowering activation energy. Demonstrate the catalytic cycle of an enzyme: how the enzyme is not permanently altered and how a product is produced from substrate(s). Report how various factors that affect enzyme function: enzyme concentration, substrate concentration, temperature, pH, salinity, competitive and non-competitive inhibitors, activators. Explain how enzymes can be regulated through feedback inhibition. Illustrate the structure of the ATP (or GTP) molecule. Explain how the structure of ATP enables it to transfer energy within the cell. 2

3 Flow of Energy Thermodynamics –Branch of chemistry concerned with energy changes Cells are governed by the laws of physics and chemistry

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 1 calorie = heat required to raise 1 gram of water 1ºC calorie or Calorie? 4

5 Weeeeee!

Energy flows into the biological world from the sun Photosynthetic organisms capture this energy Stored as potential energy in chemical bonds 6

7 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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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 9

10 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 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 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 Negative ΔG –Products have less free energy than reactants –H is lower or S is higher or both –Spontaneous (may not be instantaneous) –Exergonic 13

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 14

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 15

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17 Animation: How Enzymes Work Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at

18 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

19 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

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21 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

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 22

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25 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

26 Enzyme Action Metabolic pathways Series of enzyme-controlled reactions leading to formation of a product Each new substrate is the product of the previous reaction Enzyme names commonly: Reflect the substrate Have the suffix – ase Examples: sucrase, lactase, protease, lipase Substrate 1 Enzyme A Substrate 2 Enzyme B Substrate 3 Enzyme C Substrate 4 Enzyme D Product Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

27 Nonprotein enzymes Ribozymes 1981 discovery that certain reactions catalyzed in cells by RNA molecule itself 1.2 kinds 1.Intramolecular catalysis – catalyze reaction on RNA molecule itself 2.Intermolecular catalysis – RNA acts on another molecule

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 28

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30 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

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32 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

33 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

34 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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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 36

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