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Unformatted text preview: Biology 1A Professor Doudna Spring '10 02/12/10 8am 1 Pimentel Lecture #11: Anaerobic respira3on • Reading: Chapter 9, pp. 177‐182 • Lecture outline: – Fermenta>on – Anaerobic respira>on – Regula>on of cellular respira>on Fermenta3on and anaerobic respira3on enable cells to produce ATP without the use of oxygen • Most cellular respira>on requires O2 to produce ATP • Glycolysis can produce ATP with or without O2 (in aerobic or anaerobic condi>ons) • In the absence of O2, glycolysis couples with fermenta>on or anaerobic respira>on to produce ATP • Anaerobic respira>on uses an electron transport chain with an electron acceptor other than O2, for example sulfate • Fermenta>on uses phosphoryla>on instead of an electron transport chain to generate ATP Types of Fermenta>on • Fermenta>on consists of glycolysis plus reac>ons that regenerate NAD+, which can be reused by glycolysis • Two common types are alcohol fermenta>on and lac>c acid fermenta>on • In alcohol fermenta3on, pyruvate is converted to ethanol in two steps, with the ﬁrst releasing CO2 • Alcohol fermenta>on by yeast is used in brewing, winemaking, and baking Fig. 9‐18a 2 ADP + 2 P i 2 ATP Glucose Glycolysis 2 Pyruvate 2 NAD+ 2 NADH + 2 H+ 2 CO2 waste product 2 Ethanol (a) Alcohol fermenta3on reduced to ethanol 2 Acetaldehyde • In lac3c acid fermenta3on, pyruvate is reduced to NADH, forming lactate as an end product, with no release of CO2 • Lac>c acid fermenta>on by some fungi and bacteria is used to make cheese and yogurt • Human muscle cells use lac>c acid fermenta>on to generate ATP when O2 is scarce by cause muscle soreness Fig. 9‐18b 2 ADP + 2 P i 2 ATP Glucose recycled in the liver back into pyruvate Glycolysis 2 NAD+ 2 NADH + 2 H+ 2 Pyruvate 2 Lactate (b) Lac3c acid fermenta3on No CO2 produced Fermenta>on and Aerobic Respira>on Compared • Both processes use glycolysis to oxidize glucose and other organic fuels to pyruvate • The processes have diﬀerent ﬁnal electron acceptors: an organic molecule (such as pyruvate or acetaldehyde) in fermenta>on and O2 in cellular respira>on • Cellular respira>on produces 38 ATP per glucose molecule; fermenta>on produces 2 ATP per glucose molecule more efficient • Obligate anaerobes carry out fermenta>on or anaerobic respira>on and cannot survive in the presence of O2 • Yeast and many bacteria are faculta3ve anaerobes, meaning that they can survive using either fermenta>on or cellular respira>on • In a faculta>ve anaerobe, pyruvate is a fork in the metabolic road that leads to two alterna>ve catabolic routes Fig. 9‐19 Glucose CYTOSOL Glycolysis Pyruvate No O2 present: Fermenta3on O2 present: Aerobic cellular respira3on MITOCHONDRION Ethanol or lactate Acetyl CoA Citric acid cycle The Evolu>onary Signiﬁcance of Glycolysis • Glycolysis occurs in nearly all organisms • Glycolysis probably evolved in ancient prokaryotes before there was oxygen in the atmosphere Glycolysis and the citric acid cycle connect to many other metabolic pathways • Gycolysis and the citric acid cycle are major intersec>ons to various catabolic and anabolic pathways The Versa3lity of Catabolism • Catabolic pathways funnel electrons from many kinds of organic molecules into cellular respira>on • Glycolysis accepts a wide range of carbohydrates • Proteins must be digested to amino acids; amino groups can feed glycolysis or the citric acid cycle • Fats are digested to glycerol (used in glycolysis) and fa_y acids (used in genera>ng acetyl CoA) • Fa_y acids are broken down by beta oxida3on and yield acetyl CoA • An oxidized gram of fat produces more than twice as much ATP as an oxidized gram of carbohydrate Fig. 9‐20 Proteins Carbohydrates Fats Amino acids Sugars Glycerol FaRy acids Glycolysis Glucose Glyceraldehyde‐3‐ P NH3 Pyruvate Acetyl CoA Citric acid cycle Oxida3ve phosphoryla3on Biosynthesis (Anabolic Pathways) • The body uses small molecules to build other substances • These small molecules may come directly from food, from glycolysis, or from the citric acid cycle Regula>on of Cellular Respira>on via Feedback Mechanisms • Feedback inhibi>on is the most common mechanism for control • If ATP concentra>on begins to drop, respira>on speeds up; when there is plenty of ATP, respira>on slows down • Control of catabolism is based mainly on regula>ng the ac>vity of enzymes at strategic points in the catabolic pathway Fig. 9‐21 Glucose AMP S3mulates + – Fructose‐1,6‐bisphosphate Inhibits Glycolysis Fructose‐6‐phosphate – Inhibits Phosphofructokinase Pyruvate ATP Citrate Acetyl CoA Citric acid cycle Oxida3ve phosphoryla3on Fig. 9‐UN5 Inputs Outputs 2 + 2 NADH ATP Glycolysis Glucose 2 Pyruvate Fig. 9‐UN6 Inputs S—CoA C O CH3 2 Acetyl CoA O C COO CH2 COO 2 Oxaloacetate Outputs 2 ATP 6 NADH Citric acid cycle 2 FADH2 Fig. 9‐UN7 INTER‐ MEMBRANE SPACE H+ ATP synthase ADP + P i H+ ATP MITO‐ CHONDRIAL MATRIX Chemiosmosis h_p://en.wikipedia.org/wiki/Chemiosmosis Fig. 9‐UN8 pH diﬀerence across membrane Time Fig. 9‐UN9 You should now be able to: 1. Explain in general terms how redox reac>ons are involved in energy exchanges 2. Name the three stages of cellular respira>on; for each, state the region of the eukaryo>c cell where it occurs and the products that result 3. In general terms, explain the role of the electron transport chain in cellular respira>on 4. Explain where and how the respiratory electron transport chain creates a proton gradient 5. Dis>nguish between fermenta>on and anaerobic respira>on 6. Dis>nguish between obligate and faculta>ve anaerobes ...
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This note was uploaded on 02/27/2010 for the course BIO 1A taught by Professor Schlissel during the Spring '08 term at Berkeley.
- Spring '08