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Cellular Respiration All organisms need energy Why do we need energy? To Grow To Move To Reproduce ETC. Source of Energy • All living things require energy to maintain homeostasis • The ultimate source of energy is the SUN • Autotrophs obtain energy directly from the sun – plants, algae, and photosynthetic bacteria • Heterotrophs obtain their energy from food molecules – animals and human Photosynthesis and Respiration • Photosynthesis & respiration provide energy for life • Photosynthesis – uses solar energy to produce Glucose/O2 from CO2 & H2O • Cellular respiration – Uses O2 and makes ATP Making Energy (ATP) • Plants cells make ATP during photosynthesis • Cells of other organisms make ATP by breaking down food such as carbohydrates, fats and proteins • ATP later provides energy for cellular work ( breathing, digestion of food, muscle movement etc. ) Respiration provides energy from food Catabolic Pathways and Production of ATP • The breakdown of organic molecules is an EXERGONIC reaction • FERMENTATION is a partial degradation of sugars that occurs without O2 • AEROBIC respiration uses organic molecules such as Carbohydrates, Fat, Protein, Nucleic Acid and O2 ----- yields ATP • ANAEROBIC respiration uses compounds other than O2 Anaerobic Processes • No oxygen is required for these processes. • Includes glycolysis, the breakdown of glucose, and fermentation. • Some bacteria and yeast are examples of anaerobes. http://www.biol.vt.edu/research/images/C._perfringens_in_mac._jpg.jpg http://www.utoronto.ca/greenblattlab/images/a/yeast%201.jpg Cellular Respiration uses oxygen and glucose to produce Carbon dioxide, water, and ATP. Glucose Oxygen gas Carbon dioxide Water Energy Breathing and Cell Respiration are related O2 BREATHING CO2 Lungs CO2 Bloodstream O2 Muscle cells carrying out CELLULAR RESPIRATION Sugar + O2 ATP + CO2 + H2O How efficient is cell respiration? Energy released from glucose (as heat and light) Energy released from glucose banked in ATP Gasoline energy converted to movement About 40% 25% 100% Burning glucose in an experiment “Burning” glucose in cellular respiration Burning gasoline in an auto engine • Cellular respiration includes both aerobic and anaerobic respiration but is often used to refer to aerobic respiration • Although carbohydrates, fats, and proteins are all consumed as fuel, it is helpful to trace cellular respiration with the sugar glucose: REDOX Reactions Oxidation and Reduction • The transfer of electrons during chemical reactions releases energy stored in organic molecules • This released energy is ultimately used to synthesize ATP Redox Reactions • Chemical reactions that transfer electrons between reactants are called oxidation-reduction reactions, or redox reactions • In oxidation, a substance loses electrons, or is oxidized • In reduction, a substance gains electrons, or is reduced (the amount of positive charge is reduced) Redox reactions • Oxidation-reduction • OIL RIG (adding e- reduces + charge) • Oxidation is e- loss; reduction is e- gain • Reducing agent: e- donor • Oxidizing agent: e- acceptor becomes oxidized (loses electron) becomes reduced (gains electron) • The electron donor is called the reducing agent • The electron receptor is called the oxidizing agent • In cellular respiration, glucose is oxidized and oxygen is reduced. becomes oxidized becomes reduced NAD+ and Electron Transport Chain • In cellular respiration, glucose and other organic molecules are broken down in a series of steps • Electrons from organic compounds are usually first transferred to NAD+, a coenzyme • As an electron acceptor, NAD+ functions as an oxidizing agent during cellular respiration • Each NADH (the reduced form of NAD+) represents stored energy that is tapped to synthesize ATP Oxidizing agent in respiration • NAD+ (nicotinamide adenine dinucleotide) • Removes electrons from food (series of reactions) • NAD + is reduced to NADH Enzyme action: dehydrogenase • Oxygen is the eventual electron acceptor Electron Carriers (shuttle) • Nicotinamide Adenine Dinucleotide • (NAD+ →NADH) • FAD → FADH2 • NADH passes the electrons to the electron transport chain • ½ O2 pulls electrons down the chain and forms water • The energy yielded is used to regenerate ATP What is ATP ? • ATP stands for adenosine triphosphate • Energy carrying molecule used by cells to fuel their cellular process • ATP has – a nitrogen base adenine – a 5 carbon sugar ribose – and 3 phosphate (PO4) groups How ATP Works? • Energy is stored in bond between the 2nd and 3rd phosphate groups • When the bond is broken, energy is released and ADP is formed • ATP re - forms when ADP binds to a phosphate group ATP / ADP Cycle • ATP is constantly used and remade in the cell. • Energy is released or stored by breaking or making a phosphate bond. http://www.columbia.edu/cu/biology/courses/c2005/purves6/figure06-09.jpg Stages of Cellular Respiration •THREE stages: • GLYCOLYSIS (happens in the cytoplasm) • KREBS CYCLE or CITRIC ACID CYCLE (happens in the inner compartments of mitochondria) • ELECTRON TRANSPORT CHAIN or ETC ( in the inner membrane of mitochondria) • Summary: C6H12O6 + 6 O2 6 CO2 + 6H2O + ATP Steps of Glycolysis • Energy - requiring steps – 2 ATP added to glucose (6C) molecule to energize it – glucose split to 2 PGAL (3C) or G3P • Energy - releasing steps – each PGAL splits into pyruvate (3C) molecules – producing ATP and NADH Fig. 9-6-1 Electrons carried via NADH Glycolysis Pyruvate Glucose Cytosol ATP Substrate-level phosphorylation Fig. 9-6-2 Electrons carried via NADH and FADH2 Electrons carried via NADH Citric acid cycle Glycolysis Pyruvate Glucose Mitochondrion Cytosol ATP ATP Substrate-level phosphorylation Substrate-level phosphorylation Fig. 9-6-3 Electrons carried via NADH and FADH2 Electrons carried via NADH Citric acid cycle Glycolysis Pyruvate Glucose Oxidative phosphorylation: electron transport and chemiosmosis Mitochondrion Cytosol ATP ATP ATP Substrate-level phosphorylation Substrate-level phosphorylation Oxidative phosphorylation • The process that generates most of the ATP is called the oxidative phosphorylation because it is powered by redox reactions • It generates nearly 90% of the ATP • A smaller amount of ATP is formed in glycolysis and in the citric acid cycle by substrate-level phosphorylation Enzyme Enzyme ADP P Substrate + Product ATP An Overview of Cellular Respiration Glycolysis • The first stage of cellular respiration & fermentation • Occurs in the cytoplasm of the cell • Anaerobic ( O2 is not required) • Breaks down glucose (6 Carbon) molecule into two pyruvic acid or pyruvate (3 Carbon) molecules • It takes 2 ATP to jump – start the reactions Steps of Glycolysis • Energy - requiring steps – 2 ATP added to glucose (6C) molecule to energize it – glucose split to 2 PGAL (3C) or G3P • Energy - releasing steps – each PGAL splits into pyruvate (3C) molecules – producing ATP and NADH End Product of Glycolysis • Makes 4 ATP (2 ATP used up, net yield is 2 ATP) • 2 NADH & 2 molecules • of pyruvate (pyruvic acid) • If O2 is available to the cell - pyruvate moves into mitochondria End Products of Glycolysis • Makes 4 ATP (2 ATP used up, net yield is 2 ATP) • 2 NADH & 2 molecules • of pyruvate (pyruvic acid) • If O2 is available to the cell - pyruvate moves into mitochondria NEEDS RELEASES 2 ATP 2adp + 2p 1 GLUCOSE 2 PYRUVATE 2 NAD 2 NADh 4 ADP+4P 4 ATP Mitochondria • A large organelle with double membrane – inner fold is called cristae – central cavity known as matrix • Site of aerobic cellular respiration – energy stored in glucose is used to make ATP PREP REACTION (between glycolysis and citric acid cycle) • Occurs in the inner compartment of the mitochondrion. • 2 - Three carbon pyruvic acid is converted to 2 - Two carbon, acetyl CoA 2 CO2 2 NADH Prep Reaction • Pyruvic acid from glycolysis in mitochondria – reacts with coenzyme A, to form acetyl coenzyme (2C) – in the process CO2 and NADH are also produced Krebs Cycle (Citric Acid Cycle) • Occurs in the in the inner membrane of mitochondria • Named after the biochemist Hans Krebs • Kreb’s Cycle is also known as the Citric acid Cycle • Requires 2 cycles in order to completely oxidize one molecule of glucose (2 acetyl CoA) • Over all there are five intermediate chemical steps Krebs Cycle (Citric Acid Cycle) Results of Krebs Cycle • Each turn of the cycle makes: – 1 ATP, 3 NADH, 1 FADH2, and 2CO2 • 2 turns ( one for each pyruvate) makes: – 2 ATP, 6 NADH, 2 FADH2, and 4CO2 • CO2 is a waste product that diffuses out of the cells • NADH & FADH2 move to the electron transport chain (ETC) The Krebs Cycle Needs RELEASES 2 FAD 2 FADH2 6 NAD 6 NADH Pyruvate CO2 2ADP + 2P 2ATP Electron Transport Chain • Happens in the inner membrane • Accepts electron from NADH and FADH2 • Electrons provide energy for active transport of H+ from inner compartment to outer compartment forming a membrane potential. • H+ then pass down a concentration gradient providing energy for ATP synthase to attach a phosphate atom to ADP → ATP • Terminal electron acceptor is oxygen; thus H2O is a by-product. •Total 32 ATP are produced. Electron Transport Chain • electrons from NADH and FADH2 are passed to many electron transport enzymes which form an electron transport chain • at the end of the chain, an enzyme combines electrons from the chain, H+ (hydrogen ions) from the cell, and O2 (oxygen) to make H2O (water). • oxygen is the final electron accepter and is needed to obtain energy from NADH and FADH2 Electron Transport chain Occurs on the CRISTAE of the mitochondria The Electron Transport chain Needs Releases 2 FADH2 FAD 10 NADH NAD O2 H2O ADP + P Up to 34 ATP ATP Formation • the mitochondria accepts electrons, while some enzymes pump hydrogen ions outside the inner membrane • movement of hydrogen ions is what powers the making of ATP • the movement of a pair of electrons down the electron transport chain produces enough energy to make 3 ATP molecules from ADP ATP Formation • the more H ions on the outside makes the outside more positively charged than the inside • the difference in the charges gives the energy needed to make ATP from ADP • the mitochondrion membrane lets the enzymes pump ions out, but won’t let them come back in Electron Transport Chain Electron Transfer Phosphorylation • Electron transfer sets up H+ ion gradients • H+ concentration gradient provides energy to make ATP from ADP and Pi • Making ATP by adding Pi to ADP is called phosphorylation • Each time one electron passes to oxygen (O2) – 3 ATP are produced for each NADH – 2 ATP are produced for each FADH2 Electron Transport Chain • Cytochromes carry electron carrier molecules (NADH & FADH2) down to oxygen • Chemiosmosis: energy coupling mechanism ATP Synthase • A channel protein in the inner mitochondrial membrane • Allows H+ to diffuse down their concentration gradient, back into the inner compartment • This flow of H+ drives the formation of ATP from ADP & unbound phosphate (Pi) – oxidative phosphorylation Final ATP Tally Stage NADH Glycolysis 2 Pyruvic acid conversion 2 Krebs cycle 6 ETC FADH2 2 2 10 2 32-34 Loss due to active transport Total ATP ATP Yield -2 36-38 Summary of Energy Harvest Phosphorylation in Animal Cells • In cytoplasm (1) • In mitochondria (2, 3 & 4) Other Food Pathways 1. Carbohydrates 2. Lipids 3. Proteins Anaerobic Respiration Using Glycolysis → 2 ATP 1. Lactic Acid Fermentation Glucose → Pyruvic Acid → Lactic Acid – During periods of strenuous exercise, lactic acid may build up in muscles causing cramping. – By bacteria in food production…sour cream, yogurt, sauerkraut, pickles, kimchee 2. Ethanol Fermentation Glucose → Pyruvic Acid → Acetaldehyde → Ethanol By yeast in ethanol production of beer and wine. CO2 produced causes bread to rise Related metabolic processes • Fermentation: • 1. Alcohol: From pyruvate to ethanol • 2. Lactic acid: From pyruvate to lactate • Facultative anaerobes (yeast/bacteria) Two types of Fermentation • Alcoholic Fermentation – in yeast • Lactic acid Fermentation – in some bacteria and animal cell • Steps that follow glycolysis serve only to regenerate NAD+ Fermentation • Anaerobic extraction of energy from organic molecules – does not require oxygen • Takes place only in cytoplasm • Yields only 2 ATP • Do not break down glucose completely to CO2 and water • The ultimate electron acceptor is an organic molecule and not oxygen Lactic Acid Fermentation • Carried out by certain bacteria and animal cell • Certain bacteria utilized in food production (sour cream, yogurt, pickles) Alcoholic Fermentation • Utilized by yeast in the absence of oxygen • CO2 produced by fermentation allows bread to rise • Ethanol utilized in production of beer and wine Anaerobic respiration Glucose Glycolysis 2 Pyruvic acid Alcohol + CO2 Lactic acid Chemiosmosis • Energy released creates a proton gradient across the mitochondrial membrane • Proton gradient stores potential energy that can be used to phosphorylate ADP • Process is driven by a proton gradient (ATP synthesis proceeds as protons diffuse back across the membrane) Metabolism Catabolic Processes • Energy releasing reactions • Breakdown of large molecules to small molecules • Ingested food is the source of molecules Anabolic Processes • Energy requiring reactions • Join small molecules to form large molecules • Synthesize molecules essential to life How Important is Oxygen?? • without oxygen, electron transport can happen, but the Krebs Cycle will stop, and ATP production will also stop • if our bodies don’t get enough oxygen, then they’ll try to work from the oxygen from glycolysis • oxygen has a major role in the mitochondria of a cell Comparison • photosynthesis and respiration can be thought of as opposite reactions • photosynthesis gives energy, respiration takes energy • respiration and photosynthesis’ equations are reverse of each other • the products of photosynthesis are the reactants for the breaking down of glucose