Big Idea #2 Biological Systems utilize free energy and molecular building blocks to grow, to reproduce and to maintain dynamic homeostasis Life runs on chemical reactions rearranging atoms transforming energy organic molecules ATP & organic molecules Metabolism organic molecules ATP & organic molecules 1 solar energy 2ATP & organic molecules Energy Types of Potential Energy 3 Very difficult to define quantity The ability to do something (i.e. move) 2 general types: Potential energy- stored energy Kinetic energy moving energy 4 Gravitational Elastic Nuclear Electrical (separation of charges) Chemical (energy stored in chemical bonds) Chemical Potential Energy Kinetic Energy Moving objects Radiation (movement of light particles/waves) Thermal (heat, movement of particles) Electrical (movement of electrons) 5 6 1
7 1 st Law of Thermodynamics Energy is never created or destroyed Energy is, however, transformed from one form to another i.e. wind s motion is converted to electricity, which is converted to heat and light energy in a light bulb 8 2 nd Law of Thermodynamics The entropy of an isolated system is always increasing Entropy is the amount of energy in an unusable form usually heat Systems are always losing usable forms of energy In every conversion of energy- a lot of energy is lost as heat I.e. when you burn gas in your car- you lose a lot of energy as heat 9 What This Means 10 Put Another Way Energy will be spread from areas of high energy to low energy I.e. heat will transfer from a hot pan to the air around it A moving object will lose its kinetic energy to other objects and heat Chemicals with a lot of potential energy tend to explode releasing heat and movement of other objects 11 12 2
13 Why Do Biologists Care About This Physics Stuff? Because living things obey these laws! Living things are always losing energy to their surroundings 14 We Require an Energy Input For living things to remain whole they must have an energy input I.e. organisms must get energy from sun, deep thermal vents or eating 15 Order and Organization Require Energy Things naturally break down to keep them from breaking down or to put them together requires an input of energy 16 Energy Coupling Processes that release energy are coupled to ones that require an input of energy More energy must be released than is required for the next reaction due to entropy (energy loss) Example Exergonic Reactions 17 Flexing a muscle requires an energy input Breaking down food releases energy 18 Release free energy Used in living things to provide energy for other processes 3
The Most Significant Exergonic Reaction ATP + H 2 O ADP + Pi + Energy Hydrolysis of one of its phosphate bonds releases ADP, INORGANIC PHOSPHATE, AND FREE ENERGY Making ATP is an Endergonic Reaction It requires an input of energy Made in cellular respiration (input of chemical energy in food) This is the main molecule the body uses to transfer energy to where it is needed 19 ATP drives endergonic reactions by transfer of the phosphate group to specific reactants. 20 Energy Rxns are Coupled Living Energy Economy catabolic/anabolic ATP/ADP ADP 21 endergonic/exergonic oxidation/reduction (redox) Metabolism fuels the body s economy eat high energy organic molecules carbohydrates, lipids, proteins, nucleic acids break them down digest = catabolic; exergonic capture released energy in a form the cell can use Requires an energy currency a way to move energy around need a short term energy carrier molecule 22 ATP ATP: Adenosine Triphosphate A modified nucleotide adenine + ribose + P i AMP AMP + P i ADP ADP + P i ATP Negative PO 4 makes for unstable bonds 3rd P i is hardest to keep bonded to molecule most energy stored in 3rd P i P i group pops off easily, releasing energy ATP is unstable 23 Adding phosphates phosphorylation is endergonic Removing phosphates is exergonic energy available for cell work 24 Instability of its P i bonds makes ATP an excellent energy donor 4
ADP ATP ATP ADP releases energy 7.3 kcal/mole ATP Phosphorylation PO O O PO O O PO O O O OP O + Cal O O O O P i transferred to other molecules requires kinase ATP transfers energy Energy transferred as ATP -> ATP/ADP are cycled ATP (redox) ADP is recycled via monosaccharide metabolism (respiration) polysaccharides, lipids, not ATP, for storing energy Energy for cell work Energy from catabolism 25 26 A working muscle recycles over 10 million ATPs per second! Uses of Free Energy Maintain body temperature (some organisms) Reproduction Growth Movement reproduction movement temperature regulation Fuel for Life Bulk transport 27 28 and more Body Temperature Regulation Reproduction Endothermy Use heat released by metabolic reactions to keep a stable temp I.e. humans Ectothermy Use external sources to try to maintain body temperature I.e. snakes/reptiles Requires a huge amount of energy! Many species only reproduce when energy is available I.e. most plants flower in the spring when sunlight energy is abundant 29 30 5
Extra free energy not needed for cellular processes like movement and reproduction can be put to growth I.e. extra calories become stored fat 31 Growth 32 Energy Deprivation Mass is broken down to provide energy Eventually death will occur if there is no energy input 33 Smaller Organisms Require More Food Per Body Mass Smaller organisms have more surface area relative to volume, so they lose more heat So they must replenish that energy loss by eating more (relative to their body size) than larger animals do QUANTIFYING ENERGY total energy = useable energy* + unusable energy available for work random atomic motion OR *point of interest for biologists useable energy = total energy - unusable energy available for work random atomic motion 34 This relationship can be used to determine the energy change of a rxn: exergonic or endergonic? To Know useable = total _ unuseable energy energy energy GIBBS FREE ENERGY = ENTHALPY - ENTROPY As entropy increases, free energy decreases 35 Gibbs = enthalpy - (Temp K) disorder IfG < 0, the reaction is exergonic; occurs spontaneously; disorder is increased G is negative If G > 0, the reaction is endergonic; order/complexity is increased G is positive requires coupling with an exergonic rxn* to drive the process * usually ATP -> ADP + P 36 6
Energy released Spontaneous Exergonic G is negative 2H 2 O 2 -> 2H 2 O + 0 2 Building or breaking down molecules? Decreasing or increasing complexity? Catabolic or anabolic? Energy required Nonspontaneous Endergonic G is positive Energy stored or released? Endergonic or exergonic? Increasing or decreasing disorder? Change in G positive or negative? 37 Spontaneous or coupled with ATP? 38 Building or breaking down molecules? Decreasing or increasing complexity? Catabolic or anabolic? Energy stored or released? Gibbs Free Energy Problems Endergonic or exergonic? Increasing or decreasing disorder? Change in G positive or negative? Spontaneous or coupled with ATPrxn? 39 40 II. ENZYMES ENZYMES SPEED UP METABOLIC REACTIONS BY LOWERING ENERGY BARRIERS ENZYMES: PROTEINS THAT SERVE AS BIOLOGICAL CATALYSTS SPEED REACTIONS BY LOWERING ACTIVATION ENERGY 42 41 7
ENZYMES ARE SUBSTRATE-SPECIFIC 43 EACH TYPE OF ENZYME HAS A UNIQUE ACTIVE SITE THAT COMBINES SPECIFICALLY WITH ITS SUBSTRATE SUBSTRATE: THE REACTANT MOLECULE ON WHICH AN ENZYME ACTS UPON MECHANISM (INDUCED FIT): THE ENZYME CHANGES SHAPE SLIGHTLY WHEN IT BINDS THE SUBSTRATE 44 THE ACTIVE SITE IS AN ENZYME S CATALYTIC CENTER THE ACTIVE SITE CAN LOWER ACTIVATION ENERGY BY ORIENTING SUBSTRATES CORRECTLY, STRAINING THEIR BONDS, AND PROVIDING A SUITABLE MICRO-ENVIRONMENT 45 46 A CELL S PHYSICAL AND CHEMICAL ENVIRONMENT AFFECTS ENZYME ACTIVITY AS PROTEINS, ENZYMES ARE SENSITIVE TO CONDITIONS THAT INFLUENCE THEIR 3-D STRUCTURE EACH ENZYME HAS AN OPTIMAL TEMPERATURE AND PH 47 48 8
NOT ALL ENZYMES FUNCTION ALONE FIGURE 6.14 ENZYME INHIBITION COFACTORS: IONS OR MOLECULES FOR SOME ENZYMES TO FUNCTION PROPERLY COENZYMES: ORGANIC COFACTORS INHIBITORS: REDUCE ENZYME FUNCTION COMPETITIVE: COMPETES AND BINDS TO ACTIVE SITE NONCOMPETITIVE: BINDS TO A DIFFERENT SITE, BUT STILL INHIBITS 49 50 III. THE CONTROL OF METABOLISM METABOLIC CONTROL OFTEN DEPENDS ON ALLOSTERIC REGULATION FIGURE 6.15 ALLOSTERIC REGULATION SOME ENZYMES CHANGE SHAPE, WHEN REGULATORY MOLECULES, EITHER ACTIVATORS OR INHIBITORS, BIND TO SPECIFIC ALLOSTERIC SITES ALLOSTERIC SITE: A SPECIFIC RECEPTOR SITE ON AN ENZYME REMOTE FROM THE ACTIVE SITE. MOLECULES BIND TO THE ALLOSTERIC SITE AND CHANGE THE SHAPE OF THE ACTIVE SITE, MAKING IT EITHER MORE OR LESS RECEPTIVE TO THE SUBSTRATE 51 52 FEEDBACK INHIBITION: THE END- PRODUCT OF A METABOLIC PATHWAY ALLOSTERICALLY INHIBITS THE ENZYME FOR AN EARLY STEP IN THE PATHWAY FIGURE 6.16 FEEDBACK INHIBITION 53 54 9
6.17 COOPERATIVITY COOPERATIVITY: A SUBSTRATE MOLECULE BINDING TO ONE ACTIVE SITE OF A MULTI-SUBUNIT ENZYME ACTIVATES THE OTHER SUBUNITS THE LOCATION OF ENZYMES WITHIN A CELL HELPS ORDER METABOLISM SOME ENZYMES ARE GROUPED INTO COMPLEXES, SOME ARE INCORPORATED INTO MEMBRANES, AND OTHERS ARE CONTAINED IN ORGANELLES 55 56 10