I. Flow of Energy in Living Things II. Laws of Thermodynamics & Free Energy III. Activation Energy IV. Enzymes V. Reaction Coupling VI.

Transcription

1 Chapter 6 Energy & Metabolism I. Flow of Energy in Living Things II. Laws of Thermodynamics & Free Energy III. Activation Energy IV. Enzymes V. Reaction Coupling VI. Metabolism I. Flow of Energy in Living Things Energy = the capacity to do work Ultimately, all of the energy for living systems comes from the sun. Energy can be considered to exist in two states: A. Potential energy: stored energy! In chemical bonds! In batteries! In position Potential Energy B. Kinetic energy: energy of movement! Light (photons)! Heat (molecules)! Electricity (charged particles) Kinetic Energy! Can transfer one to the other... 1

2 Oxidation Reduction Reactions Play a Key Role in the Flow of Energy in Biological Systems Oxidation Reduction Chemistry! Oxidation: atom/molecule loses an electron or a hydrogen atom! Reduction: atom or molecule gains an electron or a hydrogen atom! Redox reactions electron lost must be gained *Energy is transferred with electrons! Oxidation Reduction Reactions Loss of electron (oxidation) A o B o e A B + A* B* Low energy High energy Gain of electron (reduction) 2

3 Nicotinamide Adenine NAD + Dinucleotide = Enzyme A major player in redox reactions NAD + = Coenzyme = Electron Carrier Molecule NAD + = oxidized = low energy NADH = reduced = high energy II. Laws of Thermodynamics & Free Energy A. First Law of Thermodynamics Energy cannot be created or destroyed, but only converted from one form to another. The total amount of energy in the universe remains constant 3

4 B. Second Law of Thermodynamics Disorder (entropy) is increasing in the universe. which is important to us because of the impacts on the transformation of Energy Energy transformations:! proceed spontaneously! more ordered to less ordered! less stable to more stable! energy dissipates as heat Heat = random motion of molecules Free Energy A Chemical reaction makes and breaks chemical bonds Convert: Reactants! Products Exergonic reactions: Energy out Reactants have more E than products Reaction liberates E Endergonic reactions: Energy in Products have more E than reactants Requires influx of E 4

5 A. Endergonic Reactions! Products of the reaction contain more energy than the reactants! These reactions will not proceed spontaneously! Require an input of energy to proceed Energy supplied Energy released Reactant Product Energy must be supplied. B. Exergonic Reactions! Products of the reaction contain less energy than the reactants! These reactions tend to proceed spontaneously! Release energy Reactant Product Energy released 5

6 IV. Activation Energy! Most reactions require an input of energy to get started; this energy is used to break existing chemical bonds and initiate chemical reactions. Energy Hurdle! The RATE of an exergonic reaction depends on the activation energy required for the reaction to begin Energy supplied Activation energy! The higher the activation energy, the slower the reaction will proceed Energy released Reactant Product! Catalysts can lower the activation energy, by helping to break chemical bonds! Catalysts can NOT change the reaction equilibrium and can NOT make an endergonic reaction proceed spontaneously! Catalysts can only lower the required activation energy Uncatalyzed Energy supplied Activation energy Catalyzed Reactant Reactant Energy released Product Product 6

7 V. Enzymes! The bulk of all catalysts used by cells are proteins called Enzymes Reactants = Substrates Substrates bind to enzymes at active site Usually a groove or depression in enzyme Enzymes are highly specific Forms enzyme-substrate complex (ES) Enzyme orients, adds charges, or strains substrate Lowering activation energy Enzymes are biological catalysts!enzyme specificity is due to the 3D shape of the active site! Induced fit Active site Substrate 7

8 ! An Enzyme can: A. Orient reactants and/or B. Add Charge 6.15 and/or C. Strain Substrate Fig. Enzyme 8.9 (TEArt) Structure and Function 1 Substrate = sucrose Bond 2 Enzymesubstrate complex H 2 O Glucose Fructose 4 Products released Active site Enzyme 3 Enzyme Stresses Substrate 8

9 Enzymes lower the activation energy of a reaction 6.14 Figure 6.14 Enzymes increase the rate of a reaction saturation point 6.16 Figure

10 Factors Affecting Enzyme Activity! Temperature! ph Temperature Effect on Enzyme Activity Rate of reaction Human Enzyme Hotsprings prokaryote Temperature of reaction ( C) ph Effect on Enzyme Activity Pepsin Trypsin Rate of reaction ph of reaction 10

11 VI. Reaction Coupling and ATP How is cellular E carried between coupled rxns? Exergonic reactions provide E for Endergonic reactions In a runner, breakdown of sugar releases E Coupled to input E to contract muscles How is E transferred between rxns? Energy Carrier molecules = Rechargable batteries Pick up E in one place in cell carry to another place in cell 1) Adenosine Triphosphate (ATP) *** Energy stored in high energy bonds Short term energy storage (versus Fats and Carbs) 2) Electron Carriers (e.g., NADH) (Nicotinamide adenine dinucleotide (NADH)) Energy is transferred with electrons Adenosine triphosphate: ATP 6.8 Figure

12 VI. Reaction Coupling and ATP [cont.] The ATP cycle ATP Phosphorylation Strongly Endergonic Hydrolysis Strongly Exergonic Energy from exergonic reactions ADP+ P Energy for endergonic reactions How is cellular E carried between coupled rxns? Example: Using glucose E to build a protein 12

13 ATP Synthesis A. ADP + Phosphate! ATP B. Mechanisms of ATP synthesis 1. Substrate Level Phosphorylation 2. Chemiosmosis = Chemiosmotic Coupling ATP Synthesis 1. Substrate-Level Phosphorylation PEP P P Enzyme P Adenosine ADP Pyruvate P P ATP P Adenosine 13

14 ATP Synthesis 2. Chemiosmosis Intermembrane space H + H + H + H + H + H + H + H+ Rotor Rod ADP + P i Enzyme=ATP Synthase Catalytic head ATP Mitochondrial matrix H + VII. Metabolism Background: Metabolism of a cell = Sum of all chemical reactions in cell Chemical reactions linked in metabolic pathways Cells couple exergonic and endergonic reactions Cells regulate chemical rxns through enzymes 14

15 Cells regulate enzyme activity (to regulate reactions) 1. Regulate synthesis synthesize enzyme only when product needed 2. Regulate active state synthesize in inactive state activate when needed 3. Noncompetitive Inhibition (Allosteric) molecule binds to other site changes active site shape 4. Competitive inhibition molecule binds to active site prevents substrate binding Cells regulate enzyme activity (to regulate reactions) 5. Feedback inhibition - Works on complex, pathway reactions - Final product feeds back and inhibits early enzyme in pathway 15

16 END Energy What is this? A major player in redox reactions NMP reactive group O H N + O CH 2 O P O H H H H OH OH O C O NH 2 AMP group O P O H O CH 2 O N N NH 2 N N H H H H H OH OH 16