Metabolism IV: VI. Anaerobic respiration VII. Chemolithotrophy VIII. Anabolism
VI. Anaerobic respiration 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
O2 A. Anaerobic respiration external terminal electron acceptor is not O2 eg. NO3- (nitrate), Fe3+, SO4-, CO2, CO32-, fumarate or another organic molecule
Oxidized electron carriers Reduced electron carriers various electron transport chains PMF Growth substrates Oxidized products succinate NO2-, N2 H2S CH4 fumarate NO3- SO42- CO2
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- NO2- nitrate reductase
N2 gas 2. Denitrification reduction of nitrate all the way to N2 through anaerobic respiration denitrification NO3- Important in agriculture and sewage treatment
S0 H2S smelly gases 3. Respiration with sulfur or sulfate • elemental sulfur or SO42- is the terminal electron acceptor SO42- H2S reduction
B. Less free energy is released in anaerobic respiration than in aerobic respiration Reduction potential Eo' (Volts) Oxidized form / Reduced form CO2 / glucose (C6H12O2) (- 0.43) 2 H+ / H2 (- 0.42) NAD+ / NADH (- 0.32) SO42- / H2S (- 0.22) pyruvate / lactate (- 0.19) fumarate / succinate (+ 0.03) NO3- / NO2- (+ 0.42) O2 / H2O (+ 0.82)
H2 + 1/2 O2 H2O Many chemolithotrophs use O2 as the terminal electron acceptor VII. Chemolithotrophy Use of inorganic compounds as the energy source (primary electron donor)
A. Examples of chemolithotrophs H2 hydrogen-oxidizing bacteria H2S sulfide-oxidizing bacteria Fe2+iron-oxidizing bacteria NH3 ammonia-oxidizing bacteria (NH3 NO2- ) NO2-nitrite-oxidizing bacteria (NO2- NO3- )
1. Example of chemolithotrophy: aerobic sulfide (H2S) oxidation inorganic electron donor Boiling sulfur pot, Yellowstone National Park SO42- + 2H+ H2S + 2 O2
Ammonia oxidizer NH3 NO2- Nitrite oxidizer NO2- NO3- 2. Examples of chemolithotrophy: ammonia oxidation and nitrite oxidation
B. Possible metabolic strategies for generating energy on early earth anaerobic chemolithotrophy fermentation anaerobic respiration anoxygenic photosynthesis
A hypothetical primitive energy- generating system on early earth primitive ATPase 2 e- ADP + Pi ATP Proton motive force (PMF) 2 H+ H2 Out primitive hydrogenase Cytoplasmic membrane In inorganic electron acceptor (not O2)
VIII. Anabolism (Biosynthesis) Nutrients Anabolism Nutrients Catabolism Macromolecules and other cell components Waste Energy Energy Energy source (eg. sugar or H2)
Polysaccharides Proteins Lipids Nucleic acids Cells are made of molecules. small molecules
A. Building cell components requires energy (ATP) reductant (NADPH) a source of carbon a source of nitrogen some P and other nutrients C H O N P S
B. Classification of organisms according to chemoorganotroph (organic chemical) phototroph (light) chemolithotroph (inorganic chemical e.g. H2S, H2, NH3) autotroph heterotroph (CO2) (organic carbon) energy source carbon source
organic carbon source (e.g. glucose) glycolysis, TCA heterotrophs nucleic acids nucleotides P, NH3 fatty acids lipid NH3 amino acids protein autotrophs CO2 C. Cell carbon Cell carbon: sugars acetyl CoA organic acids
O O D. Sugar / polysaccharide metabolism Sugars are needed for polysaccharides (cell wall, glycogen) nucleic acids (DNA, RNA) small molecules (ATP, NAD(P)+ cAMP, coenzymes, etc.) hexoses pentoses
HOCH2 O O NH O — P-O- O - O O= P-O O - O N CH2 O UDP = uridine diphosphate OH OH (don't memorize structure) 1. UDP-glucose is a precursor to polysaccharides and peptidoglycan.
2. Gluconeogenesis A pathway for making glucose-6-P from noncarbohydrate sources (e.g. acids from TCA).
3. Gluconeogenesis is the reversal of glycolysis starting with PEP, but with a few different enzymes. glucose-6-P PEP CO2 pyruvate gluconeogenesis 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
NH2 N N OCH2 O N P P P P P P N O ATP OH OH NADPH NADP+ 5. Deoxyribonucleotides for DNA are made from the reduction of the 2'- hydroxyl of ribonucleotides. NH2 N N OCH2 O N N O deoxy- ATP OH H
Sugar summary Gluconeogenesis TCA PEP OAA glycolysis glucose glucose-6-P glucose-1-P UDP-glucose (uridine diphosphoglucose) pyruvate pentose phosphate pathway ribulose-5-P UTP ribose-5-P ribonucleotides RNA deoxyribo- nucleotides DNA NADPH NADP+ polysaccharides peptidoglycan, cell walls
E. Amino acid biosynthesis 1. Requires an acid (carbon skeleton) and an amino group O C – OH H2N – C – H R carboxylic acid amino group
2. Some carbon skeletons are made 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 -KG TCA
3. The amino group for glutamate can come directly from ammonia. O C - O- O = C CH2 CH2 COO- O C - O- H3N - C - H CH2 CH2 COO- NH3 + NADP+ NADPH -ketoglutarate glutamate
4. The amino group for most other amino acids comes from glutamate through transamination (amino transfer). O C - O- O = C CH2 COO- O C - O- H3N - C - H CH2 COO- glutamate -ketoglutarate + oxaloacetate (OAA) aspartate
F. Purine and pyrimidine biosynthesis is very complex. from formyl attached to folic acid 1. The carbons and nitrogens come from amino acids, NH3, CO2, and formyl (HCOO-) groups. N N C * C * N N
2. Folic acid carries the formyl groups in purine biosynthesis. 3. Sulfanilamide is a "growth factor analog" that inhibits purine biosynthesis by inhibiting the production of folic acid.
O C~SCoA ATP, NADPH CH3 COO- D. Fatty acids 1. In general, saturated fatty acids are built two carbons at a time from acetyl CoA. (8) palmitic acid
2. Unsaturated fatty acids • have 1 or more cis-double bonds • increase fluidity of membranes COO-
3. Acetyl CoA and succinyl CoA and play important roles in anabolism. acetyl CoA fatty acid biosynthesis succinyl CoA heme biosynthesis
Study objectives 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?
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.