Energy and Metabolism Chapter 6

Section 6.1 Learning Objectives The Flow of Energy in Living Systems Differentiate between kinetic and potential energy. Identify the source of energy for the biosphere (Earth). Contrast oxidation and reduction reactions.

Flow of Energy Thermodynamics Branch of chemistry concerned with energy changes Study of energy flow or transformations Kinetic energy  potential energy Potential energy  kinetic energy Cells are governed by the laws of physics and chemistry

What is Energy? Energy – capacity to do work 2 states Kinetic – energy of motion 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? Calorie (1000 calories) how food energy measured

Copyright © The McGraw-Hill Companies, Inc Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. a. Potential energy b. Kinetic energy Stored energy based on her position (also think of a bolder on top of a hill) Energy in motion (she is able to slide down based on her previous position)

The Source of Energy on Earth Energy flows into the biological world from the sun Photosynthetic organisms (plants/algae) capture this energy Stored as potential energy in chemical bonds (in sugars made from photosynthesis) cell respiration photosynthesis

Redox reactions (how energy is transferred at molecular level) 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 LEO says GER (leo is a lion) Loss of e- is oxidation Gain of e- is reduction

To follow the energy, follow the e- Loss of electron (oxidation) LEO e- e – A B A + B A + + B – Gain of electron (reduction) GER Lower energy Higher energy

Question 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 Bloom’s level: Knowledge/Understanding

Section 6.2 Learning Objectives The Laws of Thermodynamics and Free Energy Explain the laws of thermodynamics. Relate free energy changes to the outcome of chemical reactions. Contrast the course of a reaction with and without an enzyme catalyst.

Laws of thermodynamics First law of thermodynamics Energy cannot be created or destroyed Energy 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

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

Disorder happens spontaneously Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Disorder happens spontaneously Organization requires energy © Jill Braaten

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 G

ΔG = ΔH – TS ΔG = change in free energy Positive ΔG Negative ΔG Products have more free energy than reactants Not spontaneous, requires input of energy Endergonic (photosynthesis) Negative ΔG Products have less free energy than reactants Spontaneous (may not be instantaneous) Exergonic (cell respiration)

Energy Released Energy Supplied Energy Released Energy Supplied Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Endergonic Products Energy must be supplied Energy Released Energy Supplied Free Energy (G)  G > 0 Reactants photosynthesis Course of Reaction a. Exergonic cell respiration Reactants Energy Released Energy Supplied Free Energy (G) Energy is released Products  G < 0 Course of Reaction b.

Activation Energy: How to Start a Reaction 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 Increasing energy of reacting molecules (heating) Lowering activation energy

Energy Released Energy Supplied Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. uncatalyzed catalyzed Activation energy Activation energy Energy Released Energy Supplied Free Energy (G) Reactant ΔG Product Course of Reaction

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

Energy Released Energy Supplied Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. uncatalyzed catalyzed Activation energy Activation energy Energy Released Energy Supplied Free Energy (G) Reactant ΔG Product Course of Reaction

Question The energy in a system that is able to do work is called Enthalpy Entropy Free energy Kinetic energy Potential energy Bloom’s level: Knowledge/Understanding

Question A reaction with a positive ∆G is – Exergonic Entropic Endergonic Enthalpic Energertic Bloom’s level: Knowledge/Understanding

Question A ball sitting atop a hill begins to roll down after getting a slight tap. This is analogous to an endergonic reaction. This is true This is false Bloom’s level: Application. This is exergonic. Ask how to make it endergonic

Section 6.3-6.4 Learning Objectives ATP: The Energy Currency of Cells Describe the role of ATP in short-term energy storage. Distinguish which bonds in ATP are “high energy.” Enzymes: Biological Catalysts Discuss the specificity of enzymes. Explain how enzymes bind to their substrates. List the factors that influence the rate of enzyme-catalyzed reactions.

ATP: Cell Energy 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

a. b. ATP Triphosphate group O– O P O– O ADP High-energy bonds O P O– Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. ATP Triphosphate group O– a. O P O– O ADP High-energy bonds O P O– Adenine NH2 N C O C N H C C C H N N AMP CORE O P O O CH2 O H H H H OH OH Ribose b.

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

photosynthesis cell respiration Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. + H2O ATP Energy from exergonic cellular reactions Energy for endergonic cellular processes photosynthesis + cell respiration ADP Pi

Enzymes: Biological Catalysts 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 (enzyme used to maintain blood pH) 200 molecules of carbonic acid per hour made without enzyme 600,000 molecules formed per second with enzyme

a. b. Active site Substrate Enzyme Enzyme–substrate complex Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Active site Substrate Enzyme Enzyme–substrate complex a. b.

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

consists of glucose and fructose bonded together. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 1. The substrate, sucrose, consists of glucose and fructose bonded together. 3. The binding of the substrate and enzyme places stress on the glucose– fructose bond, and the bond breaks. 2. The substrate binds to the active site of the enzyme, forming an enzyme– substrate complex. Glucose Bond Fructose H2O 4. Products are released, and the enzyme is free to bind other substrates. Active site Enzyme sucrase

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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

Enzyme function Small molecules can affect function Coenzymes Cofactors Rate of enzyme-catalyzed reaction depends on concentrations of substrate and enzyme Any chemical or physical condition that affects the enzyme’s three-dimensional shape can change rate

Optimum temperature for enzyme from hotsprings prokaryote Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Optimum temperature for human enzyme Optimum temperature for enzyme from hotsprings prokaryote Rate of Reaction 30 40 50 60 70 80 Temperature of Reaction (˚C) a. Optimum pH for pepsin Optimum pH for trypsin Rate of Reaction 1 2 3 4 5 6 7 8 9 pH of Reaction b.

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

Competitive inhibitor interferes with active site of enzyme so Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Substrate Substrate Inhibitor Inhibitor Active site Active site Enzyme Enzyme Allosteric site Competitive inhibitor interferes with active site of enzyme so substrate cannot bind Allosteric inhibitor changes shape of enzyme so it cannot bind to substrate a. Competitive inhibition b. Noncompetitive inhibition

Allosteric Enzymes 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

Question If inhibition is to be competitive, which of the following must be true? There must be more than one binding site The substrate and the inhibitor must be similar The reaction can not require a cofactor The reaction must be endergonic The allosteric and active sites must be near each other Bloom’s level: Application. Thnk in competitive, they bind the same actie site

Question 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 Substrate inhibition Allosteric inhibition Competitive inhibition Bloom’s level: Application

Question 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 Bloom’s level: Application

Section 6.5 Learning Objectives Metabolism: The Chemical Description of Cell Function Explain the kinds of reactions that make up metabolism. Discuss what is meant by a metabolic pathway. Describe mechanisms to control a metabolic pathway

Metabolism Catabolism Metabolism Anabolism Total of all chemical reactions carried out by an organism Anabolic reactions/anabolism Expend energy to build up molecules Anabolic Steroids=build muscle Catabolic reactions/catabolism Harvest energy by breaking down molecules Starvation=breakdown muscle Catabolism Anabolism Metabolism Large molecules Small molecules

Biochemical pathways Chemical reactions that create/store or produce other chemical products for daily function. Reactions occur in a sequence Product of one reaction is the substrate for the next reaction A Enzyme 1 B Enzyme 2 C Enzyme 3 D

Basic metabolic pathway chart http://upload.wikimedia.org/wikipedia/commons/1/11/Metabolism_wip.png

Initial substrate Enzyme1 Intermediate substrate A Enzyme2 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Initial substrate Enzyme1 Intermediate substrate A Enzyme2 Intermediate substrate B Enzyme3 Intermediate substrate C Enzyme4 End product

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

a. b. Initial substrate Initial substrate Enzyme 1 Enzyme 1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Initial substrate Initial substrate Enzyme 1 Enzyme 1 Intermediate substrate A Enzyme 2 Enzyme 2 Intermediate substrate B Enzyme 3 End product Enzyme 3 End product a. b.

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Question Feedback inhibition occurs when the final product acts as an inhibitor to the first enzyme in the pathway. This is true This is false Bloom’s level: Knowledge/Understanding

Question Catabolic reactions expend energy to form or transform chemical bonds. This is true This is false Bloom’s level: Knowledge/Understanding.

Final Review

Question The First Law of Thermodynamics states that energy can be – Created Destroyed Converted Lost None of the above Bloom’s level: Knowledge/Understanding

Question Small organic molecules that assist in enzymatic functions are – Coprolites Cofactors Activators Coenzymes Intermediates Bloom’s level: Knowledge/Understanding

Question Spending ATP involves hydrolyzing it into ADP and inorganic P. The energy released can drive other chemical reactions. This is true This is false Bloom’s level: Knowledge/Understanding

Question Enzymes are consumed by reactions. This is true This is false Bloom’s level: Knowledge/Understanding

Question A catalyst speeds up chemical reactions. How do catalysts do this? Decreasing entropy Altering ∆G Consuming reactants Lowering activation energy Making different products Bloom’s level: Application

Question A muscle contraction is ________, but as the muscle contracts heat is released which is ___________. Exergonic, endergonic Exergonic, exergonic Endergonic, endergonic Endergonic, exergonic Bloom’s level: Application

Question Study this metabolic pathway: A -E1  B -E2  C -E3  D. Which of the following statements is NOT correct? (E represents enzymes) C is the substrate for enzyme E1 and D is the product A is the substrate for enzyme E1 and B is the product Enzyme E2 can catalyze the substrate B but not A, C and D B is the product formed by enzyme E1 but the substrate for enzyme E2 Bloom’s level: Application

Question When muscles contract, chemical energy is converted to mechanical energy with the loss of heat. This conversion of energy is an example of the ______ Law of Thermodynamics. First Second Third Fourth Bloom’s level: Application

Question Which of the following is defined as the amount of heat required to raise one gram of water one degree Celsius? Tesla Joule Newton Calorie calorie Bloom’s level: Knowledge/Understanding