Metabolism Catabolism Anabolism Complex series of events macromolecular cell components Mediated by enzymes enzymes to interact appropriate time frame Energy Breaking down larger molecules to obtain energy and smaller particles Use of smaller precursor molecules and energy from catabolism to build o Enzymes catalyze reactions by bringing in substrates closer together at the active site This lowers the activation energy of the reaction by making it easier for the o Does not change the reaction just makes it happen in a more biologically o The products of a chemical reaction must have lower free energy than the reactants o Energy released is known as Gibbs free energy G the change in free energy G o G exergonic energy released spontaneous o G endergonic non spontaneous energy absorbed o Note endergonic and exergonic reactions must be coupled in biological systems so that no energy is wasted The exergonic reaction drives the endergonic reaction to completion o The rate at which the reaction will occur is mediated by its activation energy EA ATP o Metabolic money primary energy currency of the cell o Utilization and replenishment is an ongoing cycle o Obtained in catabolic reaction spent in anabolic reactions Electron Carriers o Molecular Shuttles o Repeatedly accept and release electrons and hydrogen to transfer redox energy o Most common carrier is NAD REDUCED to NADH H when it accepts a pair of hydrogen AND its electrons Note that electrons come with the hydrogen atoms o Recall that CO2 is a bad supplier of electrons Oxidation Reduction Reactions o Essentially electron transfers o Electron carriers are often used to transport electrons from a donor to an acceptor which results in a release of energy This energy can be conserved and used to form ATP Moving more electrons more ATP o Redox is two half reactions One is electron donating one is electron accepting Acceptor and donor together form a redox pair o Redox potential E o Energy is released when electrons flow from donors with more negative redox The tendency of a molecule to acquire electrons potentials to acceptors with more positive redox potentials o Standard reduction potential E 0 Equilibrium constant for an oxidation reduction reaction A measure of the tendency of the reducing agent to lose electrons More negative E0 better electron donor More positive E0 better electron acceptor Greater the difference between E0 of the donor and E0 of the acceptor a more negative G more energy is released Oxygen is much more positive than other terminal electron acceptors NAD NADH which explains why aerobes can make more ATP more negative G Different amounts of energy are yielded based on whether the microbe uses aerobic respiration anaerobic respiration or fermentation Fermentation yields the least amount of ATP 2 so why do most bacteria use fermentation Fermentation can happen in presence or absence of oxygen Considered an anaerobic process because it does not use oxygen as a terminal electron acceptor but fermentation can occur in the presence or absence of oxygen o Good because oxygen may not always be present in the microbe s environment Trade off only get two ATP for the ability to survive in the presence or absence of oxygen o Also no energy needs to be expended on electron transport chain since bacteria already have very limited energy even though ETC is what really amplifies the amount of ATP produced Doesn t matter what final electron acceptor is substrate level phosphorylation yields 2 ATP Glycolysis occurs in all three pathways as long as glucose is the molecule being broken down Production of ATP 3 Main Methods of ATP Synthesis 1 Substrate level phosphorylation a Essentially the process of fermentation b Transfer of a phosphate group to ADP from an intermediate molecule c Glycolysis is an example i Converts glucose into pyruvic acid pyruvate 1 Pyruvic acid a In strict aerobes and some anaerobes pyruvate enters the Krebs cycle b Can be fermented anaerobically to multiple end products c Can serve as a source of raw material for synthesizing amino acids and carbohydrates ii Multiple different pathways 1 Embden Myerhoff EMP Pathway a Traditional glycolysis b Functions with or without oxygen c Divided into 2 phases i 6 carbon phase 1 ATP phosphorylates 6 carbon glucose 2 End up with two 3 carbon compounds ii 3 Carbon phase 1 Catabolism of the 3 carbon molecules produces free energy 2 Substrate level phosphorylation yields 4 ATP molecules for a net of 2 ATP d Also produces small precursor molecules for biosynthetic reactions 2 NADH and 2 pyruvate from each glucose i NAD is needed in glycolysis to act as an oxidizing agent e Found in all 3 domains 2 Entner Duordoff ED Pathway a Useful for catabolism of carbohydrates that cant be processed by EMP i e carbohydrates containing aldehyde groups like gluconate b Produces less ATP than EMP pathway 1 net i One ATP used in the process ii Only one of the 3 carbon units yields ATP 2 ATP c Has been found in several aerobic and anaerobic bacterial d Used by soil bacteria and a few Gram negative bacteria 3 Pentose Phosphate Pathway a Technically not glycolysis because it does not produce species pyruvate b Works with does not replace the EMP pathway c Generates 1 net ATP directly d Generates 2 NADPH molecules used for reduction in biosynthetic reactions e g creating RNA e Generates multiple carbon compounds for use in other reactions f Found in most microbial organisms g Aerobic and anaerobic d TCA cycle produces 2 ATP from each pyruvate molecule yielded by glycolysis by substrate level phosphorylation 2 Photophosphorylation 3 Oxidative phosphorylation a Electrons are passed From NADH through the molecules of an electron transport b The energy from the proton gradient as they flow back into the cell proton motive chain generates a proton gradient force is used to drive ATP synthase form ATP i Substrate level phosphorylation occurs here as ADP and Pi are combined to ii Oxygen allows for the greatest amount of energy to be generated here 34 ATP Fermentation Electrons from NADH or another reduced electron carrier are passed directly to an organic electron acceptor usually pyruvate No use of an electron transport chain Anaerobic process because oxygen is not used as the terminal electron acceptor but ut can occur in the presence or absence of oxygen Not restricted to obligate anaerobes Lactic Acid Fermentation o LAB Lactic Acid Bacteria Little ATP is produced but bacteria can still grow rapidly