Chapter 9 Cellular Respiration and Fermentation Living cells require energy from outside sources Photosynthesis generates oxygen and organic molecules used by the mitochondria of eukaryotes as fuel for cellular respiration which breaks down the fuel to generate ATP The waste products of cellular respiration are the fuel for photosynthesis 9 1 Organic molecules have high potential energy because of the arrangement of their electrons between bonds Catabolic pathways yield energy by oxidizing organic fuels losing electrons Fermentation partial degradation of sugars that occurs without oxygen Aerobic respiration most prevalent and efficient catabolic pathway consumes organic molecules and oxygen Anaerobic respiration without oxygen Cellular respiration includes both anaerobic and aerobic processes Reduction the addition of electrons to a substance Electrons from organic compounds are usually first transferred to NAD which passes electrons to the ETC along with oxygen NADH reduced from NAD represents stored energy that is tapped to synthesize ATP Electron transport chain consists of a number of molecules mostly proteins 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 top higher energy end oxygen captures these electrons along with H forming water Electrons from organic compounds are usually first transferred to NAD NADH which passes electrons to the electron transport chain is reduced from NAD It represents stored energy that is tapped to synthesize ATP During cellular respiration most electrons travel the following downhill route glucose NADH electron transport chain oxygen The Three Stages of Cellular Respiration 1 Glycolysis produces 2 ATP the breakdown of glucose into two molecules of pyruvate which is oxidized into acetyl CoA which enters the 2 Citric acid cycle or Krebs cycle and Pyruvate oxidation the breakdown of glucose to carbon dioxide is completed produces 2 ATP 3 Oxidative phosphorylation ATP synthesis generates 28 ATP because it s powered by redox reactions In eukaryotic cells the inner membrane of the mitochondrion is the site of the electron transport and chemiosmosis both constitute oxidative phosphorylation Substrate level phosphorylation the production of ATP during glycolysis and the Krebs cycle Cellular respiration makes in all 32 ATP 9 2 Glycolysis occurs in the cytoplasm in two phases energy investment needs 2 ATP and energy payoff 4 produced 2 net Glycolysis occurs whether or not oxygen is present 9 3 After pyruvates are oxidized the citric acid cycle completed the energy yielding oxidation of organic molecules In the presence of oxygen the pyruvates enter the mitochondria where oxidation of glucose is complete Before entering the citric acid cycle pyruvate must be converted into acetyl CoA C3H3O3 which links glycolysis to the citric acid cycle occurs inside the membrane of mitochondria The citric acid Krebs cycle completes the breakdown of pyruvate to CO2 generates 2CO2 3NADH 1 ATP and 1 FADH2 from one pyruvate During the citric acid cycle Oxaloacetate 4 carbon waits for acetyl CoA 2 carbon forming citrate citric acid 6 carbon The next steps decompose the citrate back into oxaloacetate NADH and FADH2 relay electrons to the electron transport chain powering ATP synthesis 9 4 During oxidative phosphorylation in the electron transport chain hydrogen atoms make ATP chemiosmosis couples electron transport to ATP synthesis Electrons are passed through proteins to oxygen Electron transfer in the electron transport chain causes proteins to pump hydrogen atoms from the mitochondrial matrix to the intermembrane space Hydrogen then moves back across the membrane through the proton ATP synthase which drives the phosphorylation of ATP with the exergonic flow of hydrogen chemiosmosis Concentration movement of hydrogen atoms ATP synthesis H gradient proton motive force In cellular respiration energy flows in this sequence Glucose NADH Electron transport chain Proton motive force ATP About 34 of the energy in a glucose molecule is transferred to ATP 9 5 Fermentation and anaerobic respiration enable cells to produce ATP without oxygen The electron transport chain can t work without oxygen Without oxygen NADH accumulates Fermentation uses substrate level phosphorylation instead of the electron transport chain to produce ATP Fermentation includes glycolysis and reactions that generate NAD to accept electrons during glycolysis Lactic acid fermentation removes H to make 2 lactate temporarily holds H and electrons and regenerate 2 NAD an oxidizing agent that accepts electrons during glycolysis no release of CO2 Alcohol fermentation converts pyruvate to ethanol by releasing CO2 Comparing Fermentation with Anaerobic and Aerobic Respiration All use glycolysis In all NAD is the oxidizing agent that accepts electrons during glycolysis Different final acceptors Cellular respiration 32 ATP fermentation 2 ATP per glucose molecule Obligate anaerobes organisms that carry out only fermentation or anaerobic respiration and cannot survive in the presence of O2 Facultative anaerobes are species that can make enough ATP to survive either using fermentation or respiration yeast and bacteria pyruvate leads to either route Ancient prokaryotes used glycolysis long before oxygen 9 6 Catabolic pathways use a lot of different types of organic molecules o Carbohydrates are used in glycolysis as well as proteins amino acids and glycerol fats better o Fatty acids are broken down by beta oxidation and yield acetyl CoA Feedback inhibition controls cell respiration o Regulating activity of enzymes ATP levels