1 Chapter 6: pp Metabolism: Energy and Enzymes Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. solar energy heat Mechanical energy Chemical energy

6.1 Cells and Energy Flow What is energy? Ability to do work Allows LTs to carry out life process All depend on solar energy

3 A. Forms of Energy Kinetic: Energy of motion Mechanical Potential: Stored energy Chemical

4 Flow of Energy solar energy heat Mechanical energy Chemical energy Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

5 B. Laws of Thermodynamics First law: Law of conservation of energy Energy cannot be created or destroyed, but Energy CAN be changed from one form to another

6 Carbohydrate Metabolism Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. carbohydratemuscle contraction heat

Second law: Law of entropy When energy is changed from one form to another, there is a loss of usable energy Waste energy goes to increase disorder

8 6.2 Metabolic Reactions and Energy Transformations Metabolism: Sum of cellular chemical reactions in cell Free energy is the amount of energy available after a chemical reaction FE of reactants – FE of products → If (-) then reaction occurs spontaneously

Endergonic Reactions  Energy input required Product has more free energy than starting substances Anabolic Ex: protein synthesis, muscle contraction

Exergonic Reactions  Energy is released  Products have less free energy than starting substance  Catabolic

In which direction is this reaction anabolic? In which direction is the reaction catabolic? Where is the energy of the ATP molecule stored?

12 A. ATP and Coupled Reactions Adenosine triphosphate (ATP) High energy compound used to drive metabolic reactions Constantly being generated Composed of: Adenine and ribose (together = adenosine), and Three high energy phosphate groups Advantages Common and universal Little waste Breakdown coupled with endergonic

ATP/ADP Cycle

Coupled Reactions Rxns occur in same time and place so exergonic drives endergonic Usually exergonic = ATP hydrolysis because more energy released than consumed 2 ways to couple ATP hydrolysis ATP used to energize reactant (Cell. Resp) ATP used to change shape of reactant ( muscle contraction) Drives energetically unfavorable reactions to create order for life

Muscle Contraction

16 Work-Related Functions of ATP Primarily to perform cellular work Chemical Work - Energy needed to synthesize macromolecules Transport Work - Energy needed to pump substances across plasma membrane Mechanical Work - Energy needed to contract muscles, beat flagella, etc

Metabolic Pathways Reactions are usually occur in a sequence Products of an earlier reaction become reactants of a later reaction Such linked reactions form a metabolic pathway Begins with a particular reactant, Proceeds through several intermediates, and Terminates with a particular end product A  B  C  D  E  F  G “A” is Initial Reactant “G” is End Product B, C, D, E, and F are Intermediates

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19 Enzymes Protein molecules that function as catalysts The reactants are called substrates Regulate by eliminating side reactions Each reaction in a metabolic pathway requires a unique and specific enzyme End product will not appear unless ALL enzymes present and functional E 1 E 2 E 3 E 4 E 5 E 6 A  B  C  D  E  F  G

Four Features of Enzymes 1) Enzymes do not make anything happen that could not happen on its own. They just make it happen much faster. 2) Reactions do not alter or use up enzyme molecules. 3) The same enzyme usually works for both the forward and reverse reactions. 4) Each type of enzyme recognizes and binds to only certain substrates.

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How do enzymes lower the energy of activation?

23 A. Energy of Activation Energy must be added to at least one reactant to initiate the reaction Enzyme Operation: Enzymes operate by lowering the energy of activation Bring the substrates into contact with one another

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25 B. Enzyme-Substrate Complex Substrate = reactants Active site = small part that binds substrate specifically Induced fit modelInduced fit model – active site changes slightly for optimum fit Sometimes they participate Ex: Trypsin protein digestion

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What factors can affect the speed/rate of enzymatic reactions?

30 C. Factors Affecting Enzyme Activity Substrate concentration Increase substrate increase collisions until a max rate Amount of enzyme can also limit Temperature Enzyme activity increases with temperature Warmer temperatures cause more effective collisions between enzyme and substrate However, hot temperatures destroy enzyme

Optimal pH Normal configurations Globular structure dependent on HB between R groups Change pH will change ionization of side chains Extreme change will cause inactivity

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Temperature Increase temp, increase activity because of better collisions Will level out and then decline because of changed shape Exceptions: prokaryotes in hot springs Siamese coat color

34 Enzyme CoFactors Molecules required to activate enzyme Inorganic = Cu, Zn, Fe Coenzymes are organic cofactors Vitamins become part of conenzymes Phosphorylation – some require addition of a phosphate

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Specific Enzyme Inhibition  Irreversible Forms strong covalent bonds at active site React with -SH, -OH, or acid groups Ex: Ag, Hg, Pb Noncompetitive Reversible Changes shape, thus changing active site

37 Irreversible Inhibition Materials that irreversibly inhibit an enzyme are known as poisons Cyanides inhibit enzymes resulting in all ATP production Penicillin inhibits an enzyme unique to certain bacteria Heavy metals irreversibly bind with many enzymes Nerve gas irreversibly inhibits enzymes required by nervous system

Non-Competitive OR Allosteric Binds somewhere other than active site and changes shape of enzyme

Positive Feedback

Competitive  Inhibitor and substrate both go after active site  Example: Ethanol to acetaldehyde to acetic acid 2 nd rxn fast but Anatabuse block causing side effects Stop drinking

Negative Feedback

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What molecule does grass make available to an herbivore? What happens to this molecule during cellular respiration? Carbon dioxide is _____ to produce glucose during PS and glucose is ____ to produce ATP during CR.

6.4 Organelles and Energy Flow Photosynthesis Chloroplast capture solar energy Convert using electron transport chain to ATP Used to reduce CO 2 to glucose Cellular Respiration H atoms from C are bonded to O 2 Mitochondria breaks down carbs to produce ATP by an electron transport chain

45 Electron Transport Chain (ETC) Membrane-bound carrier proteins that pass e- from one to another Physically arranged in an ordered series Starts with high-energy e- and low-energy e- leave Each carrier is reduced and then oxidized as e- are transferred

46 A Metaphor for the Electron Transport Chain Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. high-energy electrons low-energy electrons electron transport chain ATP energy for synthesis of e e

ETCs a. are found in both mitochondria and chloroplasts b. release energy as e- are transferred c. are involved in ATP production d. are located in a membrane e. all of the above

ATP Production Chemosmosis Carriers found on thylakoid membrane of chloroplast and cristae of mitochondria H + collects on one side of the membrane Establishes an e- gradient ATP Synthase complexes

51 Chemiosmosis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. ATP synthase complex energy from electron transfers H + H + High H + concentration Low H + concentration H + pump in electron transport chain H + H + H+ H + H+ ATP ADP +P

Chemiosmosis is dependent on a. the diffusion of water across a differentially permeable membrane b. an outside supply of phosphate and other chemicals c. the establishment of an electrochemical H+ gradient

a. PS b. CR c. Both d. Neither 1. captures solar energy 2. requires enzymes and coenzymes 3. releases CO2 and H2O 4. utilizes an ETC 5. performed by plants 6. transforms one of energy into another form with the release of heat 7. creates energy for the living world