BIOL 425 CHAPTER 5 NOTESThe Flow of Energy1. Nearly every process vital to life depends on a steady flow of energy from the sun2. 13x1023 calories per year of sunlight reaches the earth3. 30% is reflected back into space4. 20% is absorbed by the atmosphere5. Almost 50% is absorbed by the earth and converted to heat6. Less than 1% is captured by the cells of photosynthetic organisms7. This energy is transformed and moved from organism to organism8. The Laws of Thermodynamicsa. Energy is the capacity to do workb. Thermodynamics is the study of energy transformationsc. The First Law of Thermodynamicsi. Energy can be changed from one form to another but cannot be created nor destroyedii. Most engines operate at less than 25% efficiency because most energyis lost as heatiii. Potential energy – the amount of energy that an object containsiv. In all energy exchanges and conversions, the total energy of the system and its surroundings after the conversion is equal to the total energy before the conversionv. Nuclear divisions do not countd. The Second Law of Thermodynamicsi. In all energy exchanges and conversion, if no energy leaves or enters the system under study, the potential energy of the final state will always be less than the potential energy of the initial stateii. A process in which the potential energy of the product is lower than that of the reactant is known as a n exergonic process – these occur spontaneouslyiii. Endergonic reactions require energy to be put iniv. Usually, exergonic reactions have a negative ΔH and an endergonic process has a positive ΔHv. Entropy1. Symbolized S2. A measurement of the disorder of a systemvi. Both the change in enthalpy (ΔH) and entropy (ΔS) contribute to the overall energy change in a systemvii. The total change is the Gibbs free energy change (ΔG)viii. ΔG=ΔH-TΔSix. Exergonic reactions – ΔG is always negative, but ΔH can be zero or even positivex. Because T is always positive, the greater ΔS is, the lower ΔG will bexi. All naturally occurring processes are exergonic9. Living organisms require a steady input of Energya. Living systems are continuously expending a large amounts of energy to maintain orderb. If equilibrium (ΔG=0) occurred, the chemical reactions of a cell would cease and the cell would diec. As time goes on, potential energy for the universe decreases and entropy increases10. Photosynthesis works by storing light energy in chemical bonds, then breaking them and converting the energy into another form11. Oxidation-Reduction (Redox)a. LEO – lose electron oxidationb. GER – gain electron, reductionc. Oxidation and reduction take place simultaneouslyd. Often, the electron lost through oxidation is carried with a proton in a hydrogenmolecule – thus, in many organic reactions, oxidation can be thought of as the loss of hydrogen atomse. Oxidation of glucose is an exergonic process (e- move to a lower energy state)f. Reduction of CO2 to sugar is endergonic (e- move to a higher energy state)g. In glucose oxidation, the energy is released in increments so that the cell doesn’t die from the rise in heat due to entropy12. Enzymesa. Most chemical reactions require an input of energy to get going – they must reach their energy of activationb. Cells use enzymes as catalysts to lower the energy of activation for many processesc. A catalyst forms a temporary association with the molecules that are reacting by bringing the reacting molecules close to one another or weakening existing bondsd. Thus, little energy is needed to carry out reactionse. Reactions go more rapidly this wayf. The catalyst is left unchanged and can be reusedg. The molecule on which an enzyme acts is the substrateh. Ribozymes are catalysts produced from RNA, but the rest are globular proteins folded in a way that they form a groove or pocketi. Active Sitei. Where the substrate fits (the pocket for it)ii. Has a precise 3-D shape and exactly the correct array of charged and uncharged areas on its binding surfacej. Cofactors in enzyme actioni. A nonprotein component necessary for the enzyme to functionii. Metal Ions1. Certain metal ions are cofactors2. Ex: Mg2+ is requird in most enzymatic reactions involving the transfer of a phosphate group from one molecule to another3. Ca2+ and K+ have similar rolesiii. Coenzymes1. Nonprotein organic cofactors2. Ex: in redox reactions, electrons are often passed along to a molecule that serves as an electron acceptor3. NAD+ is an example  it is reduced to NADHa. Consists of two ribose sugars and a phosphate bridgeb. One ribose is attached to adenine, while the other is attached to nicotinamidec. The nicotinamide ring accepts electronsd. Nicotinamide is better known as niacine. Many vitamins are precursors of coenzymes or parts of coenzymes4. Some enzymes use nonprotein cofactors called prosthetic groups  iron sulfur clusters of ferrodoxins are an example13. Metabolic Pathwaysa. Each enzyme catalyzes one step in an ordered series of reactions called a metabolic pathwayb. One pathway may be involved in the breakdown of polysaccharides, another inthe breakdown of glucose, and a third in the synethesis of an amino acidc. Groups of enzymes that make up a common pathway are often segregated inside the celld. Some are found in solutions (vacuoles) while others are found in the membranes of specialized organelles, like mitochondria and chloroplastse. If any step is exergonic, that step will use up the products of the previous step quickly, moving the process forward (creating disequilibrium)f. Some reactions are common to multiple pathwaysg. However, identical reactions that occur in different pathways are catalyzed by different enzymes, known as isozymes14. Regulation of Enzyme Activitya. Temperaturei. An increase in temperature increases the rate of enzyme-catalyzed reactionsii. When the temperature is too high, the enzyme will denature and will no longer functionb. pH works in a similar fashion to temperature – the charges of the active site will be alteredc. In each metabolic pathway, there is at least one enzyme whose activity maintains control over the rate of the sequence as a wholei. This enzyme catalyze the slowest, or rate-limiting stepii. This is a regulatory enzymeiii. Regulatory enzymes exhibit increased or decreased catalytic activity inresponse to substrate levels and certain signalsiv. Regulatory enzymes constantly adjust the rate of the sequence to meet changes in the cell’s demandsv. Often,