Summary Campbell Biology Chapter 9 PDF

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Download Summary Campbell Biology Chapter 9 PDF

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Bio Chp 9: Cellular Respiration and Fermentation -Catabolic pathways yield energy by oxidizing organic fuels -Catabolic pathways and production of ATP  Organic cmpnds have potential energy from the arrangement of electrons in the bonds b/w their atoms  Cmpnds that undergo exergonic rxs can act as fuels  Fermentation: catabolic process that is a partial degradation of sugars or other organic fuels without the presence of oxygen  Aerobic respiration: catabolic pathway in which oxygen is consumed as a reactant along with the organic fuel o Carried out by eukaryotic and prokaryotic cells o Anaerobic respiration- process that harvests chemical E without oxygen and uses other substances as reactants in prokaryotes  Cellular respiration: process that includes both aerobic and anaerobic respiration o Most closely related to aerobic respiration o Similar to combustion o Organic cmpnds + Oxygen  Carbon dioxide + water + E o C6H12O6 + 6O2  6CO2 + 6H2O + Energy (ATP + heat) o Glucose is mostly used for fuel in cells Exergonic breakdown with free energy change of -686 kcal -Redox Rxs: Oxidation and Reduction  Catabolic pathways that decompose glucose get energy from electron transfers  Principle of Redox o Redox reactions/oxidation-reduction reactions: electron transfers in a reaction o Oxidation: loss of electrons from one substance in a redox reaction o Reduction: addition of electrons to a substance in a redox rx o Reducing agent: the electron donor in a redox rx o Oxidizing agent: the electron acceptor in a redox rx o The more electronegative an atom is, the more E required to take an electron away from it C6H12O6 + 6O2  6CO2 + 6H2O + Energy (ATP + heat) Oxidized reduced  Energy harvest via NAD+ and the electron transport chain o Glucose is catalyzed in a series of steps o NAD+: coenzyme used by electron carriers to transfer hydrogen atoms to oxygen indirectly Most versatile electron acceptor that functions as an oxidizing agent during respiration o Dehydrogenases enzymes remove a pair of hydrogen atoms from the glucose substrate, thus oxidizing it (2 electrons and 2 protons) Enzyme delivers the 2 electrons along with 1 proton to its coenzyme, NAD+ Other proton is released as hydrogen ion (H+) Charge of NAD+ is neutralized with reduced to NADH (hydrogen has been received) H-C-OH+NAD+(dehydrogenase) C=O+NADH+H+ o Hydrogen and oxygen are brought together in cellular respiration to produce water Hydrogen that reacts with oxygen is derived from organic molecules rather than H2

Respiration uses electron transport chain to break the fall of electrons to oxygen into many energy-releasing steps o Electron transport chain: Molecules, mostly proteins, that are built into the inner membrane of the mitochondria of eukaryotic cells and the plasma membrane of aerobically respiring prokaryotes Electrons removed from glucose are shuttled by NADH to the higher-energy end of the ETC, where they are carried to the lower-energy end with O2 that captures these electrons along with H+ to form water Electrons cascade down the chain in a series of redox rxs, allowing only small amnt of energy to be lost until it reaches oxygen Each downhill carrier is more electronegative than uphill carrier (oxygen at end of chain) Electrons travel from glucoseNADHETCoxygen -Stages of cellular respiration: a preview  Steps: o Glycolysis o Pyruvate oxidation and the citric acid cycle o Oxidative phosphorylation: ETC and chemiosmosis  Cellular respiration is usually referred to as pyruvate oxidation, citric acid cycle, and oxidative phosphorylation (still include glycolysis for class purposes)  Pyruvate oxidation, citric acid cycle, and glycolysis are catabolic pathways  Glycolysis: process that occurs in the cytosol that begins the degradation process by breaking glucose into two molecules called pyruvate  Citric acid cycle: process where pyruvate enters the mitochondrion and is oxidized into acetyl CoA in eukaryotes  Glycolysis and citric acid cycle have redox rxs where dehydrogenase tranfers electrons from substrates to NAD+, forming NADH  Oxidative phosphorylation: mode of ATP synthesis powered by the redox reactions of the ETC o Third stage of respiration o ETC accepts electrons from the breakdown products of glycolysis and citric acid cycle and passes the electrons from one molecule to another o At end of ETC, electrons are combined with oxygen and hydrogen ions to form water o E is released at each step of the chain and is stored for the mitochondrion to make ATP from ADP  Inner membrane of mitochondrion is the site of ETC and chemiosmosis in eukaryotic cells o Process is in the plasma membrane for prokaryotic cells o Oxidative phosphorylation accounts for 90% of ATP formed by respiration  Substrate-level phosphorylation: Mechanism that creates smaller amnts of ATP that is formed directly through glycolysis and citric acid cycle o Occurs when an enzyme transfers a phosphate group from a substrate molecule to ADP o Organic molecule generated as an intermediate during the catabolism of glucose  Each molecule of glucose degraded to carbon dioxide and water by respiration makes 32 molecules of ATP, each with 7.3 kcal/mol of free E

-Glycolysis harvests chemical energy by oxidizing glucose to pyruvate  Six-carbon sugar, glucose, is split into two three-carbon sugars  Smaller sugars are oxidized and remaining atoms are rearranged to form two pyruvate  Glycolysis can be divided into two phases, energy investment and energy payoff o Cell spends ATP in energy investment phase o Energy payoff phase repays the investment phase by making ATP through substratelevel phosphorylation and NAD+ is reduced to NADH by electrons released from the oxidation of glucose o Net energy yield of glycolysis per glucose molecule is 2 ATP, 2 NADH, and 2 pyruvate  10 steps in glycolysis  No release of CO2  Occurs whether or not oxygen is present o If O2 is present, chemical E stored in pyruvate and NADH can be extracted by pyruvate oxidation, the citric acid cycle, and oxidative phosphorylation -After pyruvate is oxidized, the citric acid cycle completes the energy-yielding oxidation of organic molecules  If oxygen is present, the pyruvate enters a mitochondrion (in eukaryotic cells) where oxidation of glucose is completed  Process occurs in cytosol in prokaryotic cells -Oxidation of pyruvate to acetyl CoA  Acetyl CoA/acetyl coenzyme A: compound that pyruvate is converted to when it enters the mitochondrion through active transport o Links glycolysis and citric acid cycle  Three reactions are catalyzed o Pyruvate’s carboxyl group is removed and given off as CO2 o Two-carbon fragment is oxidized, forming acetate The extracted electrons are transferred to NAD+, storing E in the form of NADH o Coenzyme A (CoA) is attached to acetate, forming acetyl CoA, which is high in potential E Reaction of Acetyl CoA is exergonic -The Citric Acid Cycle  Also called tricarboxylic acid cycle or Krebs cycle  One pyruvate is broken down to 3 CO2 and 1 ATP through substrate-level phosphorylation  NADH and FADH2 shuttle high-energy electrons into the electron transport chain  8 steps of Krebs cycle  Acetyl CoA combines with oxaloacetate to form citrate in the first step o Citrate is the ionized form of citric acid o Oxaloacetate is regenerated o The rest of the seven steps decompose citrate back to oxaloacetate  Each pyruvate= 3 NAD+ are reduced to NADH, FAD accepts 2 electrons and 2 protons to made FADH2, 1 ATP made through substrate-level phosphorylation, and 3 CO2  NADH and FADH2 relay their electrons to ETC -During oxidative phosphorylation, chemiosmosis couples electron transport to ATP synthesis

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(4 ATP are made through citric acid cycle and glycolysis from one glucose, all through substrate-level phosphorylation) -The pathway of electron transport  Electron transport chain is a group of molecules embedded in the inner membrane of the mitochondrion in eukaryotic cells (plasma membrane for prokaryotic cells)  Components of chain are proteins (I to IV)  Prosthetic groups- nonprotein components of ETC that function in catalytic functions of enzymes that are tightly bound to the protein components  Electron carriers alternate between reduced and oxidized states through accepting and donating electrons o Components are reduced when it accepts electrons o The lower the protein the more affinity for electrons it has (more electronegative) o Components become oxidized when they pass the electrons to the downhill protein  First molecule of ETC is the flavoprotein (named from the flavin mononucleotide (FMN) it contains) o Electrons from NADH from glycolysis and citric acid cycle are transferred here o Complex 1  Flavoprotein (1)  iron-sulfer protein (complex II)  ubiquinone (coenzyme Q)  Complex III  cytochrome C  oxygen (complex IV)  Cytochromes: proteins between oxygen and ubiquinone o Have heme groups o Cytochrome cyt a3 passes electrons to oxygen  Another source of electrons if FADH2 that adds electrons at complex II  FADH2 generates less ATP then NADH because it is at a lower energy level  ETC makes no direct ATP -Chemiosmosis: the energy-coupling mechanism  ATP synthase: enzyme that makes ATP from ADP and inorganic phosphate that is located on the inner membrane of the mitochondrion or the plasma membrane of a prokaryotic cell o Uses the energy of an existing ion gradient to power ATP synthesis o Power source is based on the H+ ion gradient on opposite sides of the inner mitochondrial membrane  Chemiosmosis: process where energy stored in the form of hydrogen ion gradient across a membrane is used to drive cellular work, like the synthesis of ATP o Flow of hydrogen ions powers ATP generation o ATP synthase has four main parts made up of polypeptides Protons bind to the rotor and cause it to spin, thus catalyzing ATP production from ADP and inorganic phosphate  H+ gradient is made from the ETC o Uses the exergonic flow of electrons from NADH and FADH2 to pump H+ across the membrane, from the mitochondrial matrix into the intermembrane space o H+ had a tendency to move down the membrane, diffusing down its gradient o E stored in an H+ gradient across a membrane couples the redox reactions of the ETC to ATP synthesis  Members of the ETC accept and release protons (H+) along with electrons

Electron transfers cause H+ to be taken up and released into the solution In eukaryotic cells, ETC is in the intermembrane of the mitochondria H+ are accepted from the matrix and deposited in the intermembrane space Proton-motive force: H+ gradient that is formed from the ETC and then driven down its gradient Force drives H+ back across membrane through H+ channels by ATP synthase  Chemiosmosis is an energy-coupling mechanism that uses energy stored in the form of an H+ gradient across a membrane to drive cellular work o Energy gradient formation in mitochondria comes from exergonic redox reactions (ATP synthase is the work performed)  Chloroplasts use chemiosmosis to make ATP during photosynthesis -An Accounting of ATP Production by Cellular Respiration  Energy flow: glucoseNADHETCproton-motive forceATP  4 ATP are made directly through substrate-level phosphorylation during glycolysis and citric acid cycle  Each NADH makes 3 ATP o Estimated because true NADH ATP is not a whole number  Proton-motive force generated by redox rxs of respiration can reduce the yield of ATP  One glucose molecule could make a max of 28 ATP from oxidative phosphorylation plus 4 ATP from substrate-level phosphorylation = 32 ATP  34% of potential chemical energy in glucose is transferred to ATP o Rest lost as heat -Fermentation and anaerobic respiration enable cells to produce ATP w/o the use of oxygen  ETC chain is used in anaerobic respiration but not in fermentation  Fermentation harvests chemical E without oxygen or ETC (w/o cellular respiration) -Types of fermentation  Fermentation consists of glycolysis plus rxs that regenerate NAD+ by transferring electrons from NADH to pyruvate o NAD+ can be reused to oxidize sugar by glycolysis  Alcohol fermentation: fermentation where pyruvate is converted to ethanol in two steps o First step releases CO2 from pyruvate to form acetaldehyde o Acetaldehyde is then reduced to NADH to ethanol o Bacteria carry out alcohol fermentation under anaerobic conditions *yeast for brewing and baking  Lactic acid fermentation: fermentation where pyruvate is reduced directly by NADH to form lactate as the end product o No release of CO2 *fungi and bacteria to made dairy *human muscle cells (lactate is converted back to pyruvate to be used later with oxygen for aerobic respiration) -Comparing fermentation with anaerobic and aerobic respiration  Fermentation, anaerobic respiration, and aerobic respiration use glycolysis to oxidize glucose to pyruvate (Net production of 2 ATP through substrate-level phosphorylation) o NAD+ is the oxidizing agent o The 3 processes have different mechanisms for oxidizing NADH back to NAD+ o o o o

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Cellular respiration harvests more ATP than fermentation Obligate anaerobes: organisms that carry out fermentation only or anaerobic respiration o Cannot survive in the presence of oxygen  Facultative anaerobes: species that can make enough ATP through fermentation or respiration *yeast and bacteria *muscle cells -Evolutionary significance of glycolysis  Ancient prokaryotes are thought to have used glycolysis to make ATP before oxygen was present -Glycolysis and the citric acid cycle connect to many other metabolic pathways -The versatility of catabolism  Along with glucose, fats, proteins, and other carbohydrates can be used by respiration to make ATP o Proteins must be digested to AAs Deamination- process where amino groups in amino acids must be removed before being used in glycolysis o Beta oxidation: metabolic sequence that breaks the fatty acids down to two-carbon fragments that enter the citric acid cycle as acetyl CoA NADH and FADH2 are also generated (enter at ETC) Fats make more ATP -Regulation of cellular respiration via feedback mechanisms  Respiration is controlled by feedback inhibition  Phosphofructokinase (pacemaker of respiration) is an allosteric enzyme that has receptor sites for activators and inhibitors o Inhibited by ATP and stimulated by AMP o As ATP accumulates, inhibition occurs o Also sensitive to citrate- when citrate accumulates, it passes to cytosol and inhibits phosphofructokinase o Synchronizes the rates of glycolysis and citric acid cycle...