Cellular Respiration Metabolism sum total of life processes that build up and tear down complex molecules Anabolism build up of more complex substances from simpler ones Examples: photosynthesis protein synthesis (dehydration synthesis) Catabolism break-down of complex organic compounds to simpler ones Examples: respiration digestion (hydrolysis) Respiration includes all the chemical reactions in which energy is released in support of cellular life Where does the energy come from? In most ecosystems, energy enters as sunlight (stored in the chemical bonds of glucose) light energy trapped in organic molecules is available to both photosynthetic organisms and others that eat them organic molecules store energy in their arrangement of atoms Two types of respiration: 1. cellular respiration - uses oxygen as a reactant to complete the breakdown of a variety of organic molecules (aerobic respiration) 2. fermentation - leads to the partial degradation of sugars in the absence of oxygen (anaerobic respiration) most of the processes in cellular respiration occur in mitochondria The overall process is: Organic compounds + O 2 CO 2 + H 2 O + Energy carbohydrates, fats, and proteins can all be used as the fuel, but it is traditional to start learning with glucose Respiration Equation: C 6 H 12 O 6 + 6O 2 respiratory enzymes 6CO 2 + 6H 2 O + Energy (ATP) Cells recycle the ATP they use for work ATP, adenosine triphosphate, is the pivotal molecule in cellular energy The close packing of three negatively charged phosphate groups is an unstable, energy- storing arrangement loss of the end phosphate group stabilizes the molecule this causes the conversion of ATP to ADP and inorganic phosphate (Pi) the transfer of the terminal phosphate group from ATP to another molecule is phosphorylation How is the energy released? Oxidation/Reduction reactions = Redox Redox reactions release energy when electrons move closer to electronegative atoms Reactions that result in the transfer of one or more electrons from one reactant to another are oxidation-reduction reactions, or redox reactions Oxidation is the addition of oxygen, the removal of hydrogen, or the removal of electrons Reduction is the removal of oxygen, the addition of hydrogen, or the addition of electrons Example: The formation of table salt from sodium and chloride is a redox reaction Na + Cl Na + + Cl - Here sodium is oxidized and chlorine is reduced (its charge drops from 0 to -1) redox reactions require both a donor and acceptor oxygen is one of the most potent oxidizing agents In cellular respiration, glucose and other fuel molecules are oxidized, releasing energy Molecules that have an abundance of hydrogen are excellent fuels because their bonds are a source of electrons that move closer to oxygen these fuels do not spontaneously combine with O 2 because they lack the activation energy enzymes lower the barrier of activation energy, allowing these fuels to be oxidized slowly Cellular respiration does not oxidize glucose in a single step that transfers all the hydrogen in the fuel to oxygen at one time glucose and other fuels are broken down gradually in a series of steps, each catalyzed by a specific enzyme at key steps, hydrogen atoms are stripped from glucose and passed first to a coenzyme, like NAD + (nicotinamide adenine dinucleotide) hydrogen acceptor and thus becomes an energy storer NAD vs. NADH Dehydrogenase enzymes strip two hydrogen atoms from the fuel (glucose), pass two electrons and one proton to NAD + and release H + H-C-OH + NAD + C=O + NADH + H + this changes the oxidized form, NAD +, to the reduced form NADH NAD vs. NADH The electrons carried by NADH lose very little of their potential energy in the catabolism of glucose this energy is tapped to synthesize ATP as electrons move from NADH to oxygen unlike the explosive release of heat energy that would occur when H 2 and O 2 combine, cellular respiration uses an electron transport chain to break the fall of electrons to O 2 into several steps the electron transport chain, consisting of several molecules (primarily proteins), is built into the inner membrane of a mitochondrion NADH shuttles electrons from food to the top of the chain at the bottom, oxygen captures the electrons and H + to form water Respiration occurs in three metabolic stages: glycolysis, the Krebs cycle, and the electron transport chain and oxidative phosphorylation 1. Glycolysis occurs in the cytoplasm it begins catabolism by breaking glucose into two molecules of pyruvate anaerobic C 6 H 12 O 6 PGAL pyruvic + 4H + 4~P 2(3-C) acid intermediate compound 2 ATP activation energy 2 NAD + 4 H 2 NADH2 4 ADP + 4 P 4 ATP 2. The Krebs cycle occurs in the mitochondrial matrix it degrades pyruvate to carbon dioxide aerobic The mitochondrion is the site of: 1. active oxidative (respiratory) enzymes 2. Krebs cycle 3. electron transport system cytochromes 4. ATP synthesis Several steps in glycolysis and the Krebs cycle transfer electrons from substrates to NAD+, forming NADH NADH passes these electrons to the electron transport chain Krebs Cycle Pyruvic acid (3-C) cytosol mitochondrial matrix Acetyl CoA (2-C) Oxalacetic acid (4-C) Citric acid (6-C) 5-C 4-C CoA regenerated Coenzyme A CO 2 NAD + NADH + H + (reduced) Pyruvic Acid (3-C) Acetyl CoA (2-C) cytosol mitochondrial matrix 1 2 Oxalacetic acid (4-C) Citric Acid (6-C) (oxidized) CO 2 NAD + NADH + H + (Reduced) 5-C Acetyl CoA (2-C) 5-C 4-C CO 2 NAD + NADH + H + ADP + P i ATP is synthesized from ADP (Reduced) 3 ATP FAD FADH 2 (Reduced) 4 4-C FAD = flavin adenine dinucletide (Similar to NAD) FAD accepts e - during redox rxns H released reduces FAD to FADH 2 4-C Oxalacetic Acid NAD + NADH + H + (reduced) regenerates oxalacetic acid 5 Glucose causes 2 turns to produce 6NADH, 2FADH 2, 2ATP, and 4CO 2 3. Electron Transport System Electron carriers called cytochromes (iron containing proteins) are located in the electron transport chain within the inner mitochondrial membrane In the electron transport chain, the electrons move from molecule to molecule until they combine with oxygen and hydrogen ions to form water As they are passed along the chain, the energy carried by these electrons is stored in the mitochondrion in a form that can be used to synthesize ATP by oxidative phosphorylation In this series of oxidation reactions energy is gradually liberated to form ATP molecules 38 ATP are produced per mole of glucose that is degraded to carbon dioxide and water by respiration High energy hydrogen becomes low energy hydrogen Free O 2 does not participate in respiration until the final state when it acts as a hydrogen acceptor The low energy hydrogen combines with O 2 to form water and thus removes H 2 from the reaction ATP yield: Glycolysis - 2 Krebs cycle - 2 Electron transport - 34 Uses the flow of H + to make ATP ATP stored energy is used to: 1. build starches, fats and oils, nucleic acids, and proteins 2. supports cell activities: a. active transport b. cell division c. nerve transmission d. biosynthesis (assimilation and photosynthesis) e. muscle contraction f. bioluminescence Review of cellular respiration: cellular respiration generates many ATP molecules for each sugar molecule it oxidizes during respiration, most energy flows from glucose NADH electron transport chain proton-motive force ATP If after glycolysis oxygen is still absent fermentation results 2 forms of fermentation: 1. lactic acid fermentation - pyruvate is reduced directly by NADH to form lactate (ionized form of lactic acid) lactic acid fermentation by some fungi and bacteria is used to make cheese and yogurt muscle cells switch from aerobic respiration to lactic acid fermentation to generate ATP when O 2 is scarce The waste product, lactate, may cause muscle fatigue, but ultimately it is converted back to pyruvate in the liver Other examples: buttermilk, sauerkraut, and dill pickles 2. alcohol fermentation pyruvate is converted to ethanol in two steps first, pyruvate is converted to a two-carbon compound, acetaldehyde by the removal of CO 2 second, acetaldehyde is reduced by NADH to ethanol Examples: yeast is used in brewing and winemaking, also baking bread making In both forms of fermentation, the energy of glucose remains in the products: lactic acid and alcohol mitochondrion outer membrane cristae inner compartment NADH NAD + proton pump proton pumps e- transport chain ATP synthase P + ADP ATP ATP channel H20H20 glycolysisactiviation energy ATP glucose 6-C PGAL 3-C pyruvate 3-C anaerobic net 2 ATPs aerobic respiration anaerobic respiration Acetyl CoA 2-C Citric acid 6-C CO 2 5-C 4-C ATP net 2 ATPs net 34 ATPs e - transport chain O2O2 H2OH2O lactic acid ethyl alcohol bacteria animalsyeasts anaerobic Energy is in C3H6O3C3H6O3 C 2 H 5 OH fermentation Krebs Cycle NAD NADH FAD FADH proteincarbohydrates fat amino acids glycolysis glycerol fatty acids glucose PGAL pyruvate Acetyl CoA Citrate 6-C 5-C 4-C e - transport chain (Chemiosmosis) NH 3 urea Excretion of urine Deamination breaking off the amino group Phosphate added to glycerol converts it to PGAL Chemiosmosis forcing an ATP through a channel oxidized and split into 2-C compounds that bind with Acetyl CoA fatty acids are converted into acetyl CoA Krebs cycle keto acids