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Transcript
Cellular Respiration • The cell obtains most of its energy requirements through the of glucose (glycogen, glycerol & amino acids may also be used) • Releases the energy that is stored in • Glucose is ( ), ( to form ) and energy Releasing Stored Energy There are 3 ways of releasing the energy stored in food: 1. Aerobic cellular respiration is carried out by organisms that live in environments( ) • Examples: fungi, bacteria, plants, animals 2. Anaerobic cellular respiration is carried out by organisms that live in anaerobic environments( • Examples: nitrogen fixing bacteria, deep ocean producers 3. Fermentation - modified form of respiration • Examples: Yeast, bacteria that cause milk to sour cellular ) Aerobic Cellular Respiration • The controlled process of respiration can be divided into three groups: • 1. Glycolysis - process which converts ( )to (aka pyruvate) • 2. Kreb's ( process in which the acid yields energy in the form of • 3. Respiratory ( electron transfer system that produces ) cycle of and ) Chain - an 4 Aerobic Cellular Respiration Glycolysis • Anaerobic reaction that occurs in the • Occurs in all living cells • Does not provide enough energy to sustain life Stage of Glycolysis Summary 1. Glucose ( ) enters respiration pathway 2. Two from provide the activation energy to begin the reaction ( ) which converts glucose to (6 carbon molecule) 7 Stages of Glycolysis Summary 3. Glucose phosphate is split into (phosphoglyceraldehyde) (3 carbon molecule) 4. Each yield: forming the continues through glycolysis to , & 8 9 Stage 1 of Glycolysis 10 Stage 2 Glycolysis 11 Energy Gained from Glycolysis Glycolysis nets: 12 The Fate of Pyruvate • Pyruvate can proceed to availability of oxygen: processes dependent on the • Aerobic Cellular Respiration • Pyruvate is transported from the • Anaerobic Cellular Respiration • Pyruvate remains in the into the Preparation for the Kreb’s Cycle Transition Reaction (aka oxidative decarboxylation) • Occurs in the • Pyruvate combines with coenzyme A ( ) • Loses a carbon atom in the form of CO2 • Remaining 2 carbon molecule attaches to CoA to form Coenzyme A “tows” the acetyl group (2 carbon compound) into the Krebs cycle • During the Krebs cycle, carbon atoms are fully oxidized to carbon dioxide, NAD+ and FAD are to and , and a is produced. Krebs Cycle • The and cycle their carriers in the electron transport chain. from the Krebs to the electron • As are passed from one carrier to the next, the energy that is is used to pump hydrogen ions( ) across the mitochondrial inner membrane into the intermembrane space( ), creating a concentration( ) gradient. • The energy stored in the gradient is used to by . Krebs Cycle Citric Acid Cycle • Occurs in the mitochondria • Cycle must be completed glucose molecule • Net gains per glucose molecule: • 2 ATP • 6 NADH • 2 FADH2 per Kreb’s Cycle Steps • The 2 C combines with a 4 C called group from the transition reaction to produce a 6 C • Citric acid steps through a number of reactions, and 5C - to become a 18 Kreb’s Cycle • Ketoglutaric acid proceeds through a number of reactions losing CO2 and producing NADH and ATP to become a 4C • Succinyl acid becomes • Fumeric acid is transformed to NADH (4 C) producing FADH forming 19 Kreb’s Cycle • The oxaloacetic acid molecule the cycle ends with is not the same molecule with which the cycle began [proven using radioactive markers in glucose entering - markers end up in oxaloacetic acid] 20 21 Video – The Kreb’s Cycle 22 Electron Transport • Provides during aerobic cellular respiration • Electrons are passed down a chain of protein complexes imbedded in the inner membrane • Energy is pump hydrogen ions, H+, from the matrix into the intermembrane space • Against concentration gradient • Requires oxygen to function • Oxygen is the producing water of the electron transport system Electron Transport System • Oxidative has these high energy electrons being passed step by step to a lower energy acceptor -> oxygen • In oxidative phosphorylation a series of electron carriers, each holding the electron at a slightly energy level, pass the electrons along the pathway to • At the top of the energy hill, the electrons are held by and 24 Cytochromes • The principle components of the electron transport chain are • Composed of a protein enclosing an atom of iron each with a different capacity for holding electrons at different energy levels • The enclosed iron atom alternately and an electron passing it along to the next cytochrome at a slightly lower level of energy 25 Electron Transport System • At the end of each chain the electrons are by which then combines with protons (H+) from the solution to produce • For each of entering the electron transport chain a yield is realized • For each of entering the electron transport chain a yield is realized 26 Role of Oxygen Video – Oxidative Phosphorylation 27 C/R - Energy Harvest 28 C/R - Energy Harvest 29 Aerobic Cellular Respiration • Net gain of per 1 glucose during cellular respiration • Majority of ATP is produced using Electron Transport System and Chemiosmosis Wrap Up 31 Anaerobic Cellular Respiration • No available • Only produces the amount of ATP generated by • Converts cycle to that cannot be processed in the Krebs or • Fermentation – pathway taken by pyruvate to produce ATP in anaerobic conditions • Two types: • Lactate Fermentation • Ethanol Fermentation Lactate Fermentation • Occurs in the • Occurs when energy demands oxygen supply • Cells convert pyruvate molecules into lactate or • Use as energy source • Lactate is stored • When oxygen levels increase lactate is converted back to pyruvate • Pyruvate proceeds to Krebs cycle Ethanol Fermentation • Anaerobic process • Occurs in the of cells • Process in which yeasts and some bacteria convert pyruvate to and CO2 • Used to produce alcoholic beverages and aid in the rising of bread Anaerobic Respiration • Both types of fermentation but free NAD+ to accept H+ supplying a small amount of energy and preventing the cell from becoming acidic • Various other chemical pathways exist which allow some organisms to thrive in anoxic and hypoxic conditions 35 Summary Cellular Respiration Releases Energy from Organic Compounds - Review A. • Three metabolic pathways make up aerobic cellular respiration. B. C. Cellular Respiration Releases Energy from Organic Compounds - Review • The first set of reactions in aerobic cellular respiration is called glycolysis. • It is an anaerobic process. • During glycolysis, a small amount of ATP is generated, and NAD+ is reduced to NADH. Stage 1 of Glycolysis glucose ↓ (ATP -> ADP) [phosphorylation] a. glucose phosphate ↓ [rearranged] fructose phosphate b. ↓ (ATP -> ADP) [phosphorylation] fructose diphosphate ↓ [split] c. PGAL PGAL d. 39 Stage 2 Glycolysis PGAL PGAL ↓ NAD -> NADH DPGA a. ↓ PGA ↓ b. Pyruvate ↓ NAD -> NADH DPGA ADP -> ATP ↓ ADP -> ATP ↓ ADP -> ATP PGA ADP -> ATP Pyruvate c. 40 Cellular Respiration Releases Energy from Organic Compounds - Review • The fate of pyruvate, the final product of glycolysis, depends on the availability of oxygen and on the type of organism. • When oxygen is available, pyruvate enters the matrix of the mitochondrion. A series of reactions yield carbon dioxide and acetyl-CoA. NAD+ is reduced to NADH. Transition Reaction Cellular Respiration Releases Energy from Organic Compounds - Review • Acetyl-CoA enters the Krebs cycle by combining with a four-carbon compound. • During the Krebs cycle, two carbon atoms are fully oxidized to carbon dioxide, NAD+ and FAD are reduced to NADH and FADH2, and a small amount of ATP is produced. citrate Cellular Respiration Releases Energy from Organic Compounds - Review • The NADH and FADH2 from the Krebs cycle donate their electrons to the electron carriers in the electron transport chain. • As electrons are passed from one carrier to the next, the energy that is released is used to pump hydrogen ions across the mitochondrial inner membrane into the intermembrane space, creating a concentration gradient. • The energy stored in the gradient is used to generate ATP by chemiosmosis. Cellular Respiration Releases Energy from Organic Compounds - Review • Organisms that carry out anaerobic cellular respiration use inorganic chemicals other than oxygen as the final electron-acceptor. This produces ATP for the cell, but not as much as in aerobic respiration. breakdown of glucose in the presence of oxygen 36 ATP breakdown of glucose by lactate or ethanol fermentation 2 ATP Cellular Respiration Releases Energy from Organic Compounds - Review • In muscle that is functioning anaerobically, pyruvate is converted to lactate and the reduced NADH is reoxidized so that glycolysis can continue. This process is called lactate fermentation. Cellular Respiration Releases Energy from Organic Compounds - Review • In yeast growing anaerobically, pyruvate is converted to carbon dioxide and ethanol. This process is known as ethanol fermentation. Cellular Respiration Releases Energy from Organic Compounds - Review • Fermentation is used on an industrial scale to produce ethanol. • Ethanol is used as an additive to gasoline to reduce some environmental contaminants. Selected Fermentation Products and their Uses Chapter 5 Concept Organizer Chapter 5 Summary • P/S and C/R proceed through many different rxns to produce energy-rich compounds and break them down to release their stored energy (ATP) • When the bond to the last phosphate group is broken, leaving ADP and a free phosphate group, the energy released is available to do cellular work. • In P/S the CO2 and H2O are involved in two separate sets of reactions: • H2O is split into hydrogen ions, electrons, and oxygen in the lightdependent reactions • CO2 is incorporated into carbohydrates in the light-independent reactions. Chapter 5 Summary (cont’d) • light-dependent rxns (thylakoid membranes) capture light energy and use it to excite electrons to produce ATP and NADPH. • light-independent reactions (stroma) use the chemical potential energy of ATP and the reducing power of NADPH to reduce carbon dioxide and form glucose via the Calvin-Benson cycle. • Glucose is processed to release energy through glycolysis, the Krebs cycle, and electron transport • Glycolysis is an anaerobic process that occurs in the cytoplasm and breaks down glucose into pyruvate • Pyruvate enters the mitochondria, where it is broken down into carbon dioxide and acetyl CoA. Chapter 5 Summary (cont’d) • Acetyl CoA enters the Krebs cycle (matrix) and energy released from breakdown of compounds in the Krebs cycle is used to reduce NAD -> NADH and FAD -> FADH • NADH & FADH donate electrons to the ETC on the inner mitochondrial membranes • Energy, released as electrons, is passed along the chain & used to create a hydrogen ion gradient that powers chemiosmosis, which generates ATP. • Glycolysis is the only source of energy for some organisms. Pyruvate is broken down into carbon dioxide and alcohol (ethanol fermentation) or lactate (lactate fermentation). This process occurs anaerobically. Chapter 5 Review • What molecule provides energy for most cellular processes? • Would photosynthesis and respiration be able to proceed without enzymes? Why or why not? • Where are chlorophyll molecules found? • What happens when a compound is oxidized? Reduced? Which form contains more energy? • What occurs during chemiosmosis? Where does it occur? • What metabolic pathways are involved in cellular respiration? Where do they occur?