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Metabolism IV: VI. Anaerobic respiration VII. Chemolithotrophy VIII. Anabolism 349 VI. Anaerobic respiration 350 Reoxidation of reduced electron carriers by a process analogous to aerobic respiration, but using a terminal electron acceptor other than O2. PMF is formed and ATP is synthesized by electron transport phosphorylation. Used by microbes capable of anaerobic respiration when O2 is not available. TB 351 A. Anaerobic respiration external terminal electron acceptor is not O2 eg. NO3- (nitrate), Fe3+, SO4-, CO2, CO32-, fumarate or another organic molecule 352 Growth substrates Oxidized products Oxidized Reduced electron electron carriers carriers succinate NO2-, N2 various electron H2S transport chains CH4 PMF fumarate NO3SO42CO2 353 1. Nitrate reduction • a form of anaerobic respiration in which NO3- is the terminal electron acceptor • used by Escherichia coli and some other microorganisms when O2 is absent NO3 nitrate reductase NO2 - 354 2. Denitrification reduction of nitrate all the way to N2 through anaerobic respiration NO3 denitrification N2 gas Important in agriculture and sewage treatment 3. Respiration with sulfur or sulfate 355 • elemental sulfur or SO42- is the terminal electron acceptor 2SO4 0 S reduction H2S H2S smelly gases B. Less free energy is released in anaerobic 356 respiration than in aerobic respiration Oxidized form / Reduced form CO2 / glucose (C6H12O2) 2 H+ / H 2 NAD+ / NADH SO42- / H2S pyruvate / lactate fumarate / succinate NO3- / NO2O2 / H2O Reduction potential Eo' (Volts) (- 0.43) (- 0.42) (- 0.32) (- 0.22) (- 0.19) (+ 0.03) (+ 0.42) (+ 0.82) VII. Chemolithotrophy Use of inorganic compounds as the energy source (primary electron donor) H2 + 1/2 O2 357 H2O Many chemolithotrophs use O2 as the terminal electron acceptor A. Examples of chemolithotrophs 358 H2 H2 S 2+ Fe NH3 hydrogen-oxidizing bacteria sulfide-oxidizing bacteria iron-oxidizing bacteria ammonia-oxidizing bacteria NO2- nitrite-oxidizing bacteria (NH3 NO2- ) (NO2- NO - ) 3 1. Example of chemolithotrophy: aerobic sulfide (H2S) oxidation H2S + 2 O2 SO4 + 2- 359 + 2H inorganic electron donor Boiling sulfur pot, Yellowstone National Park 360 2. Examples of chemolithotrophy: ammonia oxidation and nitrite oxidation Ammonia oxidizer NH3 NO2- Nitrite oxidizer NO2- NO3- B. Possible metabolic strategies for generating energy on early earth anaerobic chemolithotrophy fermentation anaerobic respiration anoxygenic photosynthesis 361 A hypothetical primitive energygenerating system on early earth Proton motive force (PMF) 2 H+ H2 primitive hydrogenase 2 362 primitive ATPase Out Cytoplasmic membrane e inorganic electron acceptor (not O2) In ADP + Pi ATP VIII. Anabolism (Biosynthesis) Nutrients 363 Waste Energy Anabolism Macromolecules and other cell components Energy Catabolism Nutrients Energy source (eg. sugar or H2) 364 Cells are made of molecules. Polysaccharides Proteins Lipids Nucleic acids small molecules A. Building cell components requires energy (ATP) reductant (NADPH) a source of carbon a source of nitrogen some P and other nutrients CHONPS 365 366 B. Classification of organisms according to energy source chemoorganotroph phototroph (organic chemical) chemolithotroph (light) (inorganic chemical e.g. H2S, H2, NH3) carbon source heterotroph autotroph 367 C. Cell carbon organic carbon source (e.g. glucose) glycolysis, heterotrophs TCA nucleotides lipid Cell carbon: P, NH3 sugars fatty acetyl CoA NH 3 acids organic acids amino acids autotrophs CO2 nucleic acids protein 368 D. Sugar / polysaccharide metabolism Sugars are needed for polysaccharides (cell wall, glycogen) nucleic acids (DNA, RNA) + small molecules (ATP, NAD(P) cAMP, coenzymes, etc.) O hexoses O pentoses 1. UDP-glucose is a precursor to polysaccharides and peptidoglycan. HOCH2 O O O O O= P-O — P-O- CH2 OO- (don't memorize structure) 369 OH NH O OH N O UDP = uridine diphosphate 2. Gluconeogenesis 370 A pathway for making glucose-6-P from noncarbohydrate sources (e.g. acids from TCA). 3. Gluconeogenesis is the reversal of 371 glycolysis starting with PEP, but with a few different enzymes. glucose-6-P gluconeogenesis PEP pyruvate CO2 OAA TCA succinate 4. Pentose phosphate pathway a. makes pentoses (ribulose-5-P) from the decarboxylation of glucose-6-P b. also makes NADPH for biosynthetic reactions 372 373 5. Deoxyribonucleotides for DNA are made from the reduction of the 2'hydroxyl of ribonucleotides. NH2 N P P P OCH2 O N ATP NH2 N N N O P P P OCH2 O N OH OH NADPH OH H NADP+ N N O deoxyATP Sugar summary glycolysis glucose pyruvate glucose-6-P glucose-1-P UTP UDP-glucose Gluconeogenesis TCA374 PEP OAA pentose phosphate pathway (uridine diphosphoglucose) ribulose-5-P ribose-5-P ribonucleotides RNA NADPH NADP+ polysaccharides peptidoglycan, deoxyribocell walls nucleotides DNA E. Amino acid biosynthesis 375 1. Requires an acid (carbon skeleton) and an amino group amino group O C – OH H2 N – C – H R carboxylic acid 2. Some carbon skeletons are made 376 in glycolysis and the TCA cycle 5 main amino acid precursors a. -ketoglutarate (5C) b. oxaloacetate (4C) c. pyruvate (3C) d. phosphoglycerate (3C) e. PEP (3C), (erythrose-4-P) Carbon skeletons for amino acids (glucose) phosphoglycerate PEP CO2 (acCoA) pyruvate OAA TCA -KG 377 3. The amino group for glutamate 378 can come directly from ammonia. O C-O O=C CH2 CH2 COO- O NH3 + C-O H3N - C - H CH2 + CH2 NADP NADPH COO- -ketoglutarate glutamate 379 4. The amino group for most other amino acids comes from glutamate through transamination (amino transfer). O C - O glutamate O=C CH2 COO oxaloacetate (OAA) O -ketoglutarate C O + H3N - C - H CH2 COO aspartate F. Purine and pyrimidine is very complex. 380 biosynthesis 1. The carbons and nitrogens come from amino acids, NH3, CO2, and formyl (HCOO-) groups. N N * C C N N from formyl * attached to folic acid 2. Folic acid carries the formyl groups in purine biosynthesis. 381 3. Sulfanilamide is a "growth factor analog" that inhibits purine biosynthesis by inhibiting the production of folic acid. 382 D. Fatty acids 1. In general, saturated fatty acids are built two carbons at a time from acetyl CoA. ATP, NADPH palmitic acid 2. Unsaturated fatty acids • have 1 or more cis-double bonds • increase fluidity of membranes 383 COO- 3. Acetyl CoA and succinyl CoA and play important roles in anabolism. acetyl CoA succinyl CoA 384 fatty acid biosynthesis heme biosynthesis Study objectives 385 1. Understand anaerobic respiration and the examples presented in class. Define nitrate reduction, denitrification, sulfate reduction. 2. Understand chemolithotrophy and the examples presented in class. 3. Examples of integrative questions: Compare and contrast aerobic respiration, anaerobic respiration, chemolithotrophy, and fermentation. Given the description of a catabolic strategy, be prepared to identify the type of metabolism being used. Contrast sulfate reduction and sulfide oxidation. 4. Be able to classify microorganisms based on energy source and carbon source. 5. Understand the roles of glycolysis and the TCA cycle in the synthesis of cellular macromolecules. 6. What type of polymers are synthesized from UDP-glucose? 7. What are the functions of gluconeogenesis and the pentose phosphate pathway? 8. How are deoxyribonucleotides for DNA made from ribonucleotides? 386 10. Know the sources of carbon and nitrogen for amino acid biosynthesis. How are amino groups transferred to acids to make amino acids? 11. Understand the role of folic acid in nucleotide biosynthesis. 12. How does sulfanilamide inhibit the growth of microorganisms? 13. Humans do not make their own folates. Why is the drug sulfanilamide toxic to certain microorganisms but not to humans? 14. Know the anabolic roles of acetyl CoA and succinyl CoA as described in class.