BIOL 1441 1st Edition Lecture 14 Outline of Last Lecture I. Metabolisma. Metabolic pathwaysb. Metabolic enzymesII. Forms of energyIII. Laws of energy transformationIV. 1st law of thermodynamicsV. 2nd law of thermodynamicsVI. Free energyOutline of Current Lecture I. Exergonic ReactionsII. Endergonic ReactionsIII. Equilibrium and MetabolismIV. Energy Couplinga. ATPV. Enzymes Regulate MetabolismCurrent LectureI. Exergonic Reactionsa. Lose free energy, G decreasesb. ∆G is negative (energy being removed)These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.c. Magnitude of ∆G represents the maximum amount of work the reaction can performd. Greater the decrease in free energy, greater amount of work can be donee. Spontaneous, catabolicf. C6H12O6 + 6 O2 = 6 CO2 + 6 H2Oi. Breaking down glucoseii. ∆G = -686 kcal/moliii. For each mol of glucose (180 g) broken down by respiration, 686 kcal of energy are released that can be then used to do workII. Endergonic Reactionsa. Absorbs (consumes) free energyi. “storing” free energyb. G increases, ∆G is positivec. Nonspontaneous, anabolicd. Magnitude of ∆G is the quantity of energy required to drive the reactione. Plants use 686 kcal from sunlight to make a mol of glucosef. Convert light energy into chemical energyIII. Equilibrium and Metabolisma. Reactions in a closed system eventually reach equilibrium and then do no workb. Cells are not in equilibriumi. Open systems experiencing a constant flow of materialsc. Catabolic pathway in a cell releases free energy in a series of reactionsi. Prevent reaching equilibrium, product does not accumulateIV. Energy Couplinga. Mange energy resources to do cellular workb. Use of an exergonic process to drive an endergonic onei. Exergonic- spontaneous (release energy)ii. Endergonic- nonspontaneous (requires energy)c. Cellular Worki. Three main kinds of work use energy:1. Mechanical- beating of cilia, muscle contraction2. Transport- pump substances across membrane against the concentration gradient3. Chemical- endergonic rxn’s, synthesis of polymers from monomersd. Adenosine Triphosphate- ATPi. Provides energy for cellular functionsii. Mediates energy couplingiii. Break bonds between the phosphate groups by hydrolysis1. Hydrolysis rxn’s- add water, breaking apart polymers2. Exergonic spontaneous rxniv. Terminal phosphate bond is broken- energy is released from ATPv. ATP- “High Energy” Bonds1. Reactants (ATP & H2O) have high energy relative to the energy of the products (ADP & Pi)2. Release of energy due to chemical change to a state of lower free energy a. Complex structure-high energyb. Simple structures- lower energy 3. Physical rearrangement of molecules to lower energy statesvi. ATP- why so much energy?1. Phosphate groups negative charges2. Crowded together- repulsion- B/C NEGATIVE CHARGES3. Contributes to instability- more unstable, higher energyvii. How does ATP do work?1. Cells harness the energy released during ATP hydrolysis to performcellular work2. Energy released from ATP hydrolysis is used to drive endergonic rxn’s (nonspontaneous)a. Specific enzymes help3. When endergonic rxn requires less energy than is released by ATP hydrolysis- couple reactions a. Coupled rxn becomes exergonicviii. Coupled Rxn Exergonic1. Transfer phosphate group from ATP to another moleculea. Phosphorylation2. Key is formation of phosphorylated intermediate- more reactive, less stable, more energyix. Cellular Work1. Transport & mechanical- ATP hydrolysis leads to a change in a protein’s shape & affects it ability to bind another moleculex. Regeneration of ATP1. ATP- renewable resource 2. Regenerated by adding a phosphate group to ADP (ATP synthase)3. Energy to phosphorylate ADP comes from catabolic reactions in the cell (cellular respiration)4. ATP cycle- couples exergonic processes to endergonic processesV. Enzymes regulate metabolisma. Enzymes & Rxn Ratei. Spontaneous rxn’s will move forward on their own (exergonic rxn)1. Ex. garbage in landfill2. Takes lots of timeii. Why? Reactants (or bond) must become slightly more unstable (higher energy) before the rxn will proceed1. Absorb heat from surroundings- STRAINS BONDS=HIGH ENERGY  BREAKDOWN2. Enzyme can catalyze the rxniii. Spontaneous rxn no outside energy requirement1. Need input of energy to begin rxn- absorb from surroundings2. Occur very slowlyiv. Enzymes speed up chemical rxn’sv. Catalyst- chemical agent that speeds up a reaction without being consumed by the reaction1. Enzyme- catalytic proteinvi. Every chemical reaction between molecules involves bond breaking & bond formingvii. Changing 1 molecule into another involves contorting the starting molecule into a highly unstable state before the rxn can occurviii. To reach this unstable state, absorb energy from surroundings1. New bonds form, energy is released, return to stable shapes- lower energyb. Free Energy of Activation (EA) i. Initial energy needed to start a chemical reactionii. Often supplied in the form of heat from the surroundingsiii. Activation energy determines the rate of the rxn1. Reactants must absorb enough energy before rxn occuriv. Most rxn’s have a high activation energy & would take a very long time to proceedv. Enzymes catalyze rxn’s by lowering activation energy1. ENZYMES CANT CHANGE FREE ENERGY OF REACTANTS/PRODUCTSc. Heat & Activation Energyi. Complex molecules (protein, DNA) rich in free energyii. Have potential to decompose spontaneously1. Laws of thermodynamics favor their breakdowniii. Persist b/c at cellular temp, molecules do not absorb enough energy to overcome activation energyiv. Heat- denature proteins, kill cell, speed up all rxn’s d. Enzymes Lower Activation Energyi. Enable reactant molecules to absorb enough energy to reach the transition state even at mild temperaturesii. Enzymes do NOT affect ∆G 1. Cannot make endergonic rxn exergoniciii. They hasten reactions that would occur eventuallyiv. Very specific, only certain pathways “turned on” at any one time1. Shape determines function!e. Substrate Specificity of Enzymesi. Substrate- reactant that an enzyme acts onii. Active site- region where substrate binds enzymeiii. Forms enzyme-substrate complex (when substrate is in active site)f. Enzyme Active Sitei. Induced fit of a substrate brings chemical groups of the active site into positions that enhance their ability to catalyze the