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Transcript
Lecture 5 Microbe Metabolism Metabolism • Metabolism: • Metabolic Pathway: Two types of metabolic reactions • Catabolism or catabolic reactions: chemical reactions that break down large molecules into smaller ones • Anabolism or anabolic reactions (also called biosynthesis): chemical reactions that involve the synthesis of large molecules from smaller ones Catabolic Reaction: Cell Respiration C6H1206 + 6O2 6CO2 + 6H20 + ATP Anabolic Reaction: Photosynthesis 6CO2 + 6H20 + ATP C6H12O6 +6O2 The use of ATP in Metabolism ATP Energy for cellular work (Anabolism) Energy from Catabolism ADP + Pi ATP • Adenosine Triphosphate • Energy currency of the cell • Releases free energy when it’s phosphate bonds are broken • Allows cells to do work • It takes work to stay alive • Therefore, without ATP, there is no life Goal of this unit: to investigate how cells make ATP from compounds such as glucose Using ATP for energy Oxidation- Reduction Reactions • The production of ATP occurs by oxidation-reduction reactions • Oxidation-reduction reactions: when one or more electrons are transferred from one substance to another Oxidation-Reduction reactions • Oxidation: the loss of electrons • Reduction: the gain of electrons • Redox reactions: when both occur at the same time • When electrons removed from a compound protons often follow (H+) • Oxidation: loss of a hydrogen atom • Reduction: gain of a hydrogen atom Figure 5.9 The role of electron carriers • Cells use ATP as carrier of energy • Cells use certain molecules as carriers of electrons • 3 different electron carriers : Central Metabolic Pathways • What do they do? • Modify organic molecules in a step-wise fashion to form – Intermediates with high energy bonds that can be used to synthesize ATP – Intermediates that can be oxidized to generate reducing power – Intermediates and end products that function as precursor metabolites Aerobic Respiration Formula for Aerobic Respiration C6H12O6 +6O2 6CO2 + 6H2O +38 ATP Steps of Aerobic Respiration • Glycolysis • Transition Step • Krebs Cycle • Electron Transport Glycolysis • Primary pathway used by nearly all organisms to convert glucose to pyruvate • 10 step pathway- can occur in presence or absence of oxygen • 1 molecule of glucose split into 2 molecules of pyruvate • Generates 2 molecules of ATP and 2 molecules of NADH Glucose(6C) + 2NAD+ + 2ADP +2Pi 2 pyruvate(3C) + 2NADH + 2H+ + 2ATP Glycolysis • Net Yield of glycolysis: –2 ATP –2 NADH –2 pyruvate Transition Step • Links Glycolysis to Krebs Cycle • Pyruvate converted to acetyl Co-A • NADH generated • Net Yield of Transition Step: – 2 NADH Krebs Cycle • 8 steps of Krebs cycle complete the oxidation of glucose • Incorporates the acetyl groups from transition step, releasing CO2 • Does not directly use oxygen Krebs Cycle • Net Yield of Krebs Cycle: – 2 ATP – 6 NADH – 2 FADH2 Oxidative Phosphorylation • Uses NADH and FADH2 generated in glycolysis, the transition step, and the TCA cycle to synthesize ATP • Occurs through a combination of two mechanisms Electron Transport Chain Electron Transport Chain • As electrons fall from carrier to carrier, energy is used to form ATP • This is done by pumping protons out of the cell as electrons move along • This creates a proton gradient (proton motive force) • Energy represented in this gradient used to synthesize ATP (ATP synthase is enzyme used) Figure 5.16 (2 of 2) Electron Transport Chain • Oxidative phosphorylation in electron transport chain yields: • Each NADH generates 3 ATPs • Each FADH2 generates 2 ATPs Net ATP yield from Aerobic Respiration: • Glycolysis: 2 ATP, 2 NADH • Transition Step: 2 NADH • TCA cycle: 6 NADH, 2 FADH2, 2 ATP • Electron Transport Chain: – Add all NADH: 10 X 3= 30 – Add all FADH2: 2 X 2= 4 – Add ATP from above = 4 38 ATP Anaerobic Respiration • The same as aerobic respiration, generating ATP by phosphorylation, but uses inorganic molecule other than O2 , such as nitrate, as terminal electron acceptor • Anaerobic respiration produces less ATP than aerobic respiration Fermentation • Fermentation Produces ATP Using an Organic Electron Donors and Acceptors • Fermentation is used when oxygen and other alternative electron acceptors are unavailable • Generates 2 ATP by substrate level phosphorylation • Also generates 2 NADH- must be recycled to NAD+ • Different end products based on which microorganism Lactic Acid Fermentation Eukaryotes also perform fermentation, such as the yeast used in alcoholic fermentation to create alcoholic beverages Photosynthesis • • • • Starting substances: carbon dioxide, water Ending substances: glucose and oxygen Two types of organisms: Oxygenic Photosynthesis: – produces oxygen and glucose – Uses light energy from the sun • Anoxygenic Photosynthesis: – Do not produce oxygen – Water not starting substance, instead hydrogen sulfide