Ch 9. Respiration and Energy PDF

Cellular Respiration Harvesting Chemical Energy.. Figure 9.1 How do these leaves power the wor1l: of life KEY CONCEPTS for the giant panda? 9.1 Catabolic pathways yield energy by oxidizing organic fuels 9.2...

Cellular Respiration Harvesting Chemical Energy.. Figure 9.1 How do these leaves power the wor1l: of life KEY CONCEPTS for the giant panda? 9.1 Catabolic pathways yield energy by oxidizing organic fuels 9.2 Glycolysis harvests chemical energy by oxidizing glucose to pyruvate 9.3 The citric acid cycle completes the energy- yielding oxidation of organic molecules 9.4 During oxidative phosphorylation, chemiosmosis couples eleelron transport to AlP synthesis 9.5 Fermentation and anaerobic respiration enable Organic + 0 molecules 2 cells to produce ATP without the use of oxygen Cellular respiration /} 9.6 Glycolysis and the citric acid cycle connect to many other metabolic pathways In mltochondna t::-/ r'Di;ri 1i,..- Life Is Work iving cells require transfusions of energy from outside L sources to perform their many tasks-for example, assem· bUng polymers, pumping substances across membranes, moving, and reproducing. The giant panda in Figure 9.1 obtains energy for its cells by eating plants; some animals feed on other or- ganisms that eat plants. The energy stored in the organic mol-.. Figure 9.2 Energy flow and chemical ~c1ing in ecules offood ultimately comes from the sun. Energy flows into an ecosystems. Energy flows into an ecosystem as sunlight and ultimately ecosystem as sunlight and leaves as heat (Figure 9.2). In contrast, leaves as heat, while the ehermeal elements essential to life are recyded. the chemical elements essential to life are recycled Photosynthe- r~:i::::~C9~:thways sis generates oxygen and organic molecules used by the mito- chondria of eukaryotes (including plants and algae) as fuel for cellular respiration. Respiration breaks this fuel down, generating yield energy ATP. The waste products of this type of respiration, carbon diox- by oxidizing organic fuels ide and water, are the raw materials for photosynthesis. In this chapter, we consider how cells harvest the chemica.l energy stored As you learned in Chapter 8, metabolic pathways that release in organic mokcWes and use it to generate ATP, the molecule stored energy by breaking down complex molecules are called thatdri\'esmostceUularwork.Afterpresentingsomebasicsabout catabolic pathways. Electron transfer playsa major role in these respiration. we will focus on the three key path....'ays ofrespiration: pathways. In this section, we consider these processes, which glycolysis. the dtric acid cycle, and oxidati\-e phosphorylation. are central to ceUular respiration. 162 Catabolic Pathways and Production of AlP from ADP and (p), (see Figure 8.12). To understand how cellu- lar respiration accomplishes this, let's examine the fundamen- Organic compounds possess potential energy as a result of tal chemical processes known as oxidation and reduction. their arrangement of atoms. Compounds that can participate in exergonic reactions can act as fuels. With the help of en- Redox Reactions: Oxidation and Reduction zymes, a cell systematically degrades complex organic mol- ecules that are rich in potential energy to simpler waste products How do the catabolic pathways that decompose glucose and that have less energy. Some of the energy taken out of chemi- other organic fuels yield energy? The answer is based on the cal storage can be used to do work; the rest is dissipated as heat. transfer of electrons during the chemical reactions. The relo- One catabolic process, fermentation, is a partial degrada- cation of electrons releases energy stored in organic mol- tion ofsugars that occurs without the use of oxygen. However, ecules, and this energy ultimately is used to synthesize ATP. the most prevalent and efficient catabolic pathway is aerobic respiration, in which oxygen is consumed as a reactant along The Principle of Redox with the organic fuel (aerobic is from the Greek aer, air, and In many chemical reactions, there isa transferofoneor moreelec- bios, life). The cells of most eukaryotic and many prokaryotic trons (e-) from one reactant to another. These electron transfers organisms can carry out aerobic respiration. Some prokary- are called oxidation-reduction reactions, or redox reactions for otes use substances other than oxygen as reactants in a similar short. In a redox reaction, the loss ofelectrons from one substance process that harvests chemical energy without using any oxy- is called oxidation, and the addition ofelectrons to another sub- gen at all; this process is called anaerobic respiration (the pre- stance is known as reductioIL (Note thataddillgelectrons is called fix an- means Uwithoun. Te of respiration, the electron transport chain accepts electrons ele oxygen. Later in this chapter, you from the breakdown products of the first two stages (most of~ will learn more about how the cell uses the energy released ten via NADH) and passes these electrons from one molecule from this exergonic electron fall to regenerate its supply of to another. At the end ofthe chain, the electrons are combined ATP. For now, having covered the basic redox mechanisms of with molecular oxygen and hydrogen ions (H+), forming wa~ cellular respiration, let's look at the entire process. ter (see Figure 9.5b). The energy released at each step of the chain is stored in a form the mitochondrion (or prokaryotic The Stages of Cellular Respiration: A Preview cell) can use to make ATP. This mode of ATP synthesis is Respiration is a cumulative function ofthree metabolic stages: called oxidative phosphorylation because it is powered by the redox reactions of the electron transport chain. L Glycolysis (color-coded teal throughout the chapter) In eukaryotic cells, the itmer membrane of the mitochondrion 2.1lie CitriC aCla cle color-coaea salmon is the site of electron transport and chemiosmosis, the processes 3. Oxi ative p osphory ation: e eetron transport an that together constitute oxidative phosphorylation In prokaryotes, chemiosmosis (color-coded violet) these processes take place in the plasma membrane. Oxidative Cellular respiration is sometimes defined as including only the phosphorylation accounts for almost m ofthe ATP generated by citric acid cycle and oxidative phosphorylation. We include respiration Asmaller amountofATP is formed directly in a few re- glycolysis, however, because most respiring cells deriving en~ actions ofglycolysis and the citric acid cycle by a mechanism called ergy from glucose use this process to produce starting mate~ substrate-level phosphorylation (Figure 9.7). This mode of rial for the citric acid cycle. ATP synthesis occurs when an enzyme transfers a phosphate As diagrammed in Figure 9.6, the first two stages of cellu- group from a substrate molecule to ADP, rather than adding an lar respiration, glycolysis and the citric acid cycle, are the inorganic phosphate to ADP as in oxidative phosphorylation... Figure 9.6 An overview of cellular respiration. DUring glycolysis. each glucose molecule is broken down into two molecules r Electrons Electrons carried of the compound pyruvate, In eukaryotic cells. earned via NADH and as shown here. the pyruvate enters the via NADH FADH 2 mitochondrion. where the citric acid cycle oxidizes it to carbon dioxide. NADH and a ~t~ Similar electron carrier. a coenzyme called FADH Redox Reactions: Oxidation and Reduction The cell oxidation of organic molecules (pp. 170-172) taps the energy stored in food molecules through redox re- actions. in which one substance partially or totally shifts... In eukaryotic cells, the import of pyruvate into the mitochon- electrons to another. The substance receiving electrons is drion and its conversion to acetyl CoA links glycolysis to the reduced; the substance losing electrons is oxidized. During citric acid cycle. (In prokaryotic cells, the citric acid cycle oc- cellular respiration, glucose (C 6 H 120 6 ) is oxidized to CO 2 , curs in the cytosol.) and O 2 is reduced to H20. Electrons lose potential energy Input~ Outputs during their transfer from organic compounds to oxygen. Electrons from organic compounds are usually passed first to NAO+, reducing it to NADH. NADH passes the electrons to an electron transport chain, which conducts them to O 2 in energy-releasing steps. The energy is used to make ATP. 2 Aeetyl CoA... lhe Stages of Cellular Respiration: A Prcvicw Glycolysis and the citric acid cycle supply electrons (via NADH or FAOH 2) to the electron transport chain, which drives oxidative phosphorylation. Oxidative phosphorylation generates AlP. _&!4.if. OXilloaeetate BioFlix 3-D Animation Cdlular Respiration ACllvity Build a Chemical Cycling System ACllvity Overview of Cellular Respiration -M4oI',· Acti,ity The Citric Add Cycle 182 UNIT TWO The Cell _i· lili, , _ 9.4.. The Evolutionary Significance of Glycolysis Glycolysis occurs in nearly all organisms and probably evolved in ancient During oxidative phosphorylation, chemiosmosis prokaryotes before there was O 2 in the atmosphere. couples electron transport to ATP synthesis (pp, 172-177) -$IN',· Acth'lly Fcrmentation ~ NADH and FADH 2 donate electrons to the electron trans- port chain, which powers ATr synthesis via oxidative phosphorylation. - i ll14.,-9.6.. The Pathway of Electron Transport In the electron trans- Glycolysis and the citric acid cycle connect to many port chain, electrons from NADH and FADH 2 lose energy in other metabolic pathways (pp. 180-182) several energy-releasing steps. At the end ofthe chain, elec- trons are passed to 02> reducing it to H20... The Versatility of Catabolism Catabolic pathways funnel electrons from many kinds of organic molecules into cellular.. Chemiosmosis: The Energy- , respiration. INTER- Coupling Mechanism At MEMBRANf , certain steps along the I.. Biosynthesis (Anabolic Pathways) Cells can use small mol- SPACE electron transport chain, ecules from food directly or use them to build other sub- electron transfer causes protein complexes in eu- "' stances through glycolysis or the citric acid cycle... Regulation of Cellular Respiration via Feedback Mecha- karyotes to move H+ from nisms Cellular respiration is controlled by allosteric enzymes the mitochondrial matrix " at key points in glycolysis and the citric acid cycle. to the intermembrane space, storing energy as a proton-motive force (H+ -1- Iynthase ATP gradient). As H+ diffuses back into the matrix TESTING YOUR KNOWLEDGE through ATP synthase. its passage drives the phos- SELF-QUIZ phorylation of ADP. ADP + ®, ,re Prokaryotes generate an L \Xfhat is the reducing agent in the following reaction? MITO- H+ gradient across their CHONDRIAL Pyru\"Jte + NADH + H+ Lactate + NAD+ plasma membrane and use MATRIX this gradient to synthesize a. oxygen d. lactate ATP in the cell. b. NAOH e. pyru\"Jte.. An Accounting of ATP Production by Cellular Respira- c. NAO+ tion About 4()% of the energy stored in a glucose molecule is 2. The immediate energy source that drives ATP synthesis by transferred to ATP during cellular respiration, producing a maximum of ahout 38 ATP. ATP synthase during oxidative phosphorylation is the a. oxidation of glucose and other organic compounds. -51401"· "IF] Tutor Cdlular Respiration Part 2-Citrk Add Cyde and Electron b. flow of electrons down the electron transport Transport chain. ActMty Elcctron Transport c. affinity of oxygen for electrons. RiologyLab~ On.Line Mitochondrial.lIb d. H+ concentration across the membrane holding ATP In\"eStigation How Is thc Rate of Cellular Respiration Measured' synthase. e. transfer of phosphate to AOP. -i· II14.,-9.5 3. Which metaholic pathway is common to hoth fermentation Fermentation and anaerobic respiration enable and cellular respiration of a glucose molecule? cells to produce ATP without the use of oxygen a. the citric acid cycle (pp, 177-179) b. the electron transport chain.. Types of Fermentation Glycolysis nets 2 ATP by substrate- c. glycolysis level phosphorylation, whether oxygen is present or not. Un- d. synthesis of acetyl CoA from pyruvate der anaerobic conditions, either anaerobic respiration or e. reduction of pyruvate to lactate fermentation can take place. In anaerobic respiration, an elec- tron transport chain is present with a final electron acceptor 4. In mitochondria, exergonic redox reactions other than oxygen. In fermentation, the electrons from a. are the source of energy driving prokaryotic ATP NADH are passed to pyru\"Jte or a derivative of pyruvate, re- synthesis. generating the NAD + required to oxidize more glucose. Two common types of fermentation are alcohol fermentation and b. are directly coupled to substrate-level phosphorylation. lactic acid fermentation. c. provide the energy that establishes the proton gradient. ~ Fermentation and Aerobic Respiration Compared Both d. reduce carbon atoms to carbon dioxide. use glycolysis to oxidize glucose but differ in their final elec- e. are coupled via phosphorylated intermediates to tron acceptor. Respiration yields more ATP. endergonic processes. (IlP,PTH NINE Cellular Respiration: Harvesting Chemical Energy 183 5. The final electron acceptor of the electron transport chain that 10. l/Will The graph here shows the pH difference across functions in aerobic oxidative phosphorylation is the inner mitochondrial membrane over time in an actively a. oxygen. respiring cell. At the time indicated by the vertical arrow, a b. water. metabolic poison is added that specifically and completely c. NAD1-. inhibits all function of mitochondrial ATP synthase. Draw d. pyruvate. what you would expect to see for the rest of the graphed line. e. ADP. 6. When electrons flow along the electron transport chains of mitochondria, which of the following changes occurs? t a. The pH of the matrix increases. b. ATP synthase pumps protons by active transport. c. The electrons gain free energy. d. The cytochromes phosphorylate ADP to form ATP. e. NAD +- is oxidized. 7. Cells do not catabolize carbon dioxide because Time_ a. its double bonds are too stable to be broken. b. CO 2 has fewer bonding electrons than other organic compounds. For Self-Quiz amwers, see Appendix A. c. CO 2 is already completely reduced. d. CO 2 is already completely oxidized. -$14·".- Visit the Study Area at www.masteringbio.com for a e. the molecule has too few atoms. Practice Test. 8. Which of the following is a true distinction between fermenta- EVOLUTION CONNECTION tion and cellular respiration? II. ATP synthases are found in the prokaryotic plasma membrane and a. Only respiration oxidizes glucose. in mitochondria and chloroplasts. What does this suggest about the b. NADH is oxidized by the electron transport chain in evolutionary relationship of these eukaryotic organelles to prokary- respiration only. otes? How might the amino acid sequences of the ATP synthases c. Fermentation, but not respiration, is an example of a from the different sources support or refute your hypothesis? catabolic pathway. d. Substrate-level phosphorylation is unique to SCIENTIFIC INQUIRY fermentation. 12. In the 194{)s, some physicians prescribed low doses of a drug e. NAD+ functions as an oxidizing agent only in respiration. called dinitrophenol (DNP) to help patients lose weight. This 9. Most CO2 from catabolism is released during unsafe method was abandoned after a few patients died. DNP a. glycolysis. uncouples the chemiosmotic machinery by making the lipid b. the citric acid cycle. bilayer of the inner mitochondrial membrane leaky to H+. c. lactate fermentation. Explain how this causes weight loss. d. electron transport. SCIENCE, TECHNOLOGY, AND SOCIETY e. oxidative phosphorylation. 13. Nearly all human societies use fermentation to produce alco- holic drinks such as beer and wine. The practice dates back to the earliest days of agriculture. How do you suppose this use of fermentation was first discovered? Why did wine prove to be a more useful beverage, especially to a preindustrial culture, than the grape juice from which it was made? 8iolollicallnquiry: A Workl>ook of InYestigath'c Case. Explore fermenta' t;on further in the case "Bean 8rew.- 184 UNlr TWO The Cell