Microbial Metabolism Lecture Notes PDF

LS MCRB 121 Microbiology Lectures 4-5 Microbial Metabolism ©McGraw-Hill Education  Introduction All cells need to accomplish two fundamental tasks Synthesize new parts Cell...

LS MCRB 121 Microbiology Lectures 4-5 Microbial Metabolism ©McGraw-Hill Education  Introduction All cells need to accomplish two fundamental tasks Synthesize new parts Cell walls, membranes, ribosomes, nucleic acids Harvest energy to power reactions Sum of chemical reactions in a cell is called metabolism Implications of microbial metabolism Biofuels Food and beverage production Important in laboratory Important models for study Unique pathways are potential drug targets ©McGraw-Hill Education ©Comstock/Getty Images  Principles of Microbial Metabolism - Figure 6.1 Can separate metabolism into two parts Catabolism Processes that degrade compounds to release energy Cells capture to make ATP Anabolism or biosynthesis Assemble subunits of macromolecules Use ATP to drive reactions Processes intimately linked Jump to Principles of Microbial Metabolism - Figure 6.1 Long Description ©McGraw-Hill Education  Energy - Figure 6.2 Energy is the capacity to do work Two types of energy: Potential: stored energy (chemical bonds, rock on hill, water behind dam) Kinetic: energy of motion (moving water) Energy in universe cannot be created or destroyed, but it can be changed from one form to another ©McGraw-Hill Education © Farrell Grehan/Science Source  Energy - Figure 6.3 Photosynthetic organisms harvest energy in sunlight Power synthesis of organic compounds from CO2 Convert kinetic energy of Radiant energy (sunlight) Photosynthetic organisms harvest the energy of sunlight and use it to power the synthesis of organic compounds from CO2. This converts photons to potential energy radiant energy to chemical energy. of chemical bonds Chemoorganotrophs obtain energy from organic compounds Depend on activities of Chemical energy Chemoorganotrophs degrade organic (organic compounds) compounds, harvesting chemical energy. photosynthetic organisms or chemolithoautotrophs ©McGraw-Hill Education Top: ©Robert Glusic/Getty Images; Bottom: ©Digital Vision/PunchStock  Energy Free energy is energy available to do work Energy released when chemical bond is broken Exergonic reactions: reactants have more free energy than products Energy is released in reaction Endergonic reactions: products have more free energy than reactants Reaction requires input of energy Change in free energy for a given reaction is the same regardless of number of steps involved Cells use multiple steps when degrading compounds Energy released from exergonic reactions powers endergonic reactions ©McGraw-Hill Education  Components of Metabolic Pathways - Figure 6.4 Metabolic pathway Series of chemical reactions that converts starting compound to an end product May be linear, branched, cyclical a) Linear metabolic p athway b) Branched metabolic pathway c) Cyclical metabolic p athway ©McGraw-Hill Education  Components of Metabolic Pathways - Figure 6.5 Role of Enzymes Biological catalysts: speed up conversion of substrate into product by lowering activation energy Specific enzyme required for each step of a metabolic pathway Without enzymes, energy-yielding reactions would occur too slowly ©McGraw-Hill Education  Components of Metabolic Pathways - Figure 6.6 Role of ATP Adenosine triphospate (ATP): energy currency of cell Composed of ribose, adenine, three phosphate groups Cells use energy to produce ATP by adding Pi to adenosine diphosphate (ADP) Energy released by removing Pi from ATP to yield ADP ©McGraw-Hill Education  Components of Metabolic Pathways (1) Processes that generate ATP Some bacteria, most Chemoorganotrophs notably the Streptococci, acquire Substrate-level phosphorylation all of their energy for growth and Energy generated in exergonic reactions metabolism from substrate-level Oxidative phosphorylation phosphorylation. Energy generated by proton motive force Photosynthetic organisms Photophosphorylation Sunlight used to create proton motive force ©McGraw-Hill Education  Components of Metabolic Pathways - Figure 6.7a When electrons move from molecule that has low affinity for electrons (energy source) to a molecule that has high affinity for electrons (terminal electron acceptor), energy is released a) Energy is released when electrons are moved from an energy source with a low affinity for electrons to a terminal electron acceptor with a higher affinity. Jump to Components of Metabolic Pathways - Figure 6.7a Long Description ©McGraw-Hill Education  Components of Metabolic Pathways - Figure 6.7b More energy released when difference in electronegativity (affinity for electrons) is greater b) Three examples of c) Three examples of chemoorganotrophic chemolithotrophic metabolism metabolism Jump to Components of Metabolic Pathways - Figure 6.7b Long Description ©McGraw-Hill Education  Components of Metabolic Pathways - Figure 6.8 Prokaryotes use remarkably diverse energy sources and terminal electron acceptors Organic, inorganic compounds used as energy sources O2, other molecules used as terminal electron acceptors Electrons removed through series of oxidation-reduction reactions or redox reactions Substance that loses electrons is oxidized Substance that gains electrons is reduced Electron-proton pair, or hydrogen atom, is transferred Dehydrogenation = oxidation X loses electron(s). Hydrogenation = reduction Y gains electron(s). X is the reducing agent. X is oxidized by the reaction. Y is reduced by the reaction. Y is the oxidizing agent. ©McGraw-Hill Education  Components of Metabolic Pathways (2) The Role of Electron Carriers Energy harvested in stepwise process Electrons initially transferred to electron carriers Can be considered hydrogen carriers NAD + NADH , NADP + NADPH , and FAD∕FADH2 Reduced electron carriers represent reducing power Easily transfer electrons to chemicals with higher affinity for electrons Raise energy level of recipient molecule Ultimately drive synthesis of ATP or biosynthesis ©McGraw-Hill Education  Overview of Catabolism (1) Two key sets of processes Oxidizing glucose molecules to generate ATP, reducing power (NADH, FADH2, and NADPH), and precursor metabolites; accomplished in a series of reactions called the central metabolic pathways. Transferring the electrons carried by NADH and FADH2 to the terminal electron acceptor, which is done by either cellular respiration or fermentation (the electrons carried by NADPH are used in biosynthesis). ©McGraw-Hill Education  Overview of Catabolism (2) Central metabolic pathways oxidize glucose to CO2 Catabolic, but precursor metabolites and reducing power can be diverted for use in biosynthesis Termed amphibolic to reflect dual role Glycolysis Splits glucose (6C) to two pyruvate molecules (3C) Generates modest ATP, reducing power, precursors Pentose phosphate pathway Primary role is production precursor metabolites, NADPH Tricarboxylic acid (TCA) cycle With transition step, oxidizes pyruvate; releases CO2 Generates reducing power, precursor metabolites, ATP ©McGraw-Hill Education  Overview of Catabolism - Figure 6.10 ©McGraw-Hill Education Jump to Overview of Catabolism - Figure 6.10 Long Description  Overview of Catabolism (3) Respiration (or cellular respiration) transfers electrons from glucose to electron transport chain (ETC) to terminal electron acceptor Electron transport chain generates proton motive force Harvested to make ATP by oxidative phosphorylation Aerobic respiration O2 is terminal electron acceptor Anaerobic respiration Molecule other than O2 as terminal electron acceptor Modified version of TCA cycle ©McGraw-Hill Education  Overview of Catabolism (4) Fermentation recycles electron carriers in a cell that cannot respire so that it can continue to make ATP Use of pyruvate or a derivative as terminal electron acceptor to receive H from NADH Regenerates NAD + so that glycolysis can continue Glycolysis provides small amount of ATP ©McGraw-Hill Education  Table 6.3 ATP-Generating Processes of Prokaryotic Chemoorganoheterotrophs Metabolic Uses an Terminal ATP Generated by ATP Generated by Total ATP Process Electron Electron Substrate-Level Oxidative Generated Transport Acceptor Phosphorylation Phosphorylation (Theoretical Chain (Theoretical (Theoretical Maximum) Maximum) Maximum) Aerobic Yes O2 2 in glycolysis (net) 34 38 respiration 2 in the TCA cycle 4 total Anaerobic Yes Molecule other Number varies; Number varies; Number varies; respiration than O2 such as however, the ATP yield however, the ATP yield however, the ATP yield nitrate ( NO3− ) , of anaerobic of anaerobic of anaerobic nitrite ( NO −2 ) , respiration is less than respiration is less than respiration is less than sulfate ( SO 24− ) that of aerobic that of aerobic that of aerobic respiration but more respiration but more respiration but more than that of than that of than that of fermentation. fermentation. fermentation. Fermentation No Organic molecule 2 in glycolysis (net) 0 2 (pyruvate or a 2 total derivative) ©McGraw-Hill Education  Enzymes (1) Enzymes are biological catalysts; they increase the rate of a reaction Enzymes are highly specific for substrate(s) Enzyme not changed by reaction so a single molecule can be used again and again Name reflects function; ends in -ase ©McGraw-Hill Education  Enzymes - Figure 6.11 Active site on surface of enzyme binds substrate(s) weakly Causes enzyme shape to change slightly, induced fit Resulting enzyme-substrate complex destabilizes existing bond or allows new ones to form Lowers activation energy of reaction Jump to Enzymes - Figure 6.11 Long Description ©McGraw-Hill Education ©Kenneth Edward/BioGrafx/Science Source  Enzymes (2) Enzymes are used to break large molecules into smaller ones or to build large molecules from its subunits Theoretically enzyme-catalyzed reactions are reversible, but free energy of some reactions prevents reversibility ©McGraw-Hill Education  Enzymes - Figure 6.12 Table 6.4 Some Coenzymes and Their Function Cofactors assist some enzymes Cofactors can assist different enzymes; Include magnesium, zinc, copper, other trace elements Coenzymes are organic cofactors Include electron carriers FAD, NAD + , NADP + ; fewer types needed Derived from vitamins Coenzyme Vitamin from Which It Substance Transferred Example of Use Is Derived Coenzyme A Pantothenic acid (vitamin B5 ) Acyl groups Carries the acetyl group that enters the TCA cycle Flavin adenine dinucleotide Riboflavin (vitamin B2) Hydrogen atoms (2 electrons Carrier of reducing power (FAD) and 2 protons) Nicotinamide adenine Niacin (vitamin B3) Hydride ions (2 electrons and Carrier of reducing power ( dinucleotide NAD + ) 1 proton) Pyridoxal phosphate Pyridoxine (vitamin B6 ) Amino groups Transfers amino groups in amino acid synthesis Tetrahydrofolate Folate/folic acid (vitamin B9 ) 1-carbon molecules 1-carbon donor in nucleotide synthesis Thiamin pyrophosphate Thiamine (vitamin B1) Aldehydes Helps remove CO2 from pyruvate in the transition step ©McGraw-Hill Education  Enzymes - Figure 6.13 Environmental Factors Influence Enzyme Activity Enzymes have narrow range of optimal conditions Temperature, pH, salt concentration 10 degrees Celsius increase doubles speed of enzymatic reaction up to maximum proteins denature at higher temperatures Low salt, neutral pH usually optimal ©McGraw-Hill Education  Enzymes - Figure 6.14 Allosteric Regulation Enzyme activity controlled by regulatory molecule binding to allosteric site Distorts enzyme shape, prevents or enhances binding of substrate to active site Regulatory molecule is usually end product of metabolic pathway Allows feedback inhibition Jump to Enzymes - Figure 6.14 Long Description ©McGraw-Hill Education  Enzymes - Figure 6.15 Enzyme Inhibition In competitive inhibition, inhibitor binds to active site Chemical structure of inhibitor usually similar to substrate Concentration dependent; inhibitor blocks substrate Example is sulfa drugs that block folate synthesis Jump to Enzymes - Figure 6.15 Long Description ©McGraw-Hill Education  Table 6.5 Characteristics of Enzyme Inhibitors Enzyme Inhibition In non-competitive inhibition, inhibitor binds to a site other than the active site Allosteric inhibitors are one example; action is reversible Some non-competitive inhibitors are not reversible Mercury oxidizes the S—H groups of amino acid cysteine, converts to cystine Cystine cannot form important disulfide bond (S—S) Enzyme changes shape, becomes nonfunctional Type Characteristics Competitive inhibition Inhibitor binds to the active site of the enzyme, blocking access of the substrate to that site. Competitive inhibitors such as sulfa drugs are used as antibacterial medications. Non-competitive Inhibitor changes the shape of the enzyme, so that the substrate can no longer bind the inhibition (by regulatory active site. This is a reversible action that cells use to control the activity of allosteric molecules) enzymes. Non-competitive Inhibitor permanently changes the shape of the enzyme, making the enzyme non- inhibition (by enzyme functional. Enzyme poisons such as mercury are used in certain antimicrobial compounds. poisons) ©McGraw-Hill Education  Lecture 4,5 (Chapter 6) Review (part 1) What is metabolism? Differentiate Catabolism and Anabolism What is the difference between potential and kinetic energy? What would be cellular analogs of potential and kinetic energy? Define chemoorganotrophs What is role of ATP in the cell? What are three mechanisms by which ATP can be synthesized in bacterial cells? Define oxidation and reduction within the context of cellular metabolic reactions What role do electron carriers play in metabolic reactions? How does NAD +/NADH + H+ function as an electron/hydrogen carrier? What are the two processes of catabolism? (Slide 15) What is the central metabolic pathway of a cell? Define respiration and fermentation What are enzymes and what role do they play in chemical reactions? What are most enzymes composed of? What are the exceptions? What is the enzyme active site? Define and differentiate ”competitive enzyme inhibitors” and “non-competitive enzyme inhibitors What is allosterism? ©McGraw-Hill Education  Metabolism Part 2 ©McGraw-Hill Education  The Central Metabolic Pathways (1) Central metabolic pathways generate: ATP Reducing power: NADH, FADH2, NADPH Precursor metabolites Different glucose molecules have different fates Can be completely oxidized to CO2 generating maximum ATP Can be siphoned off as precursor metabolite for use in biosynthesis Will not produce maximum ATP ©McGraw-Hill Education Table 6.6 Comparison of the Central Metabolic Pathways Pathway Characteristics Glycolysis Glycolysis generates: 2 ATP (net) by substrate-level phosphorylation 2 NADH + 2 H + six different precursor metabolites Pentose phosphate The pentose phosphate cycle generates: cycle NADPH + H + (amount varies) two different precursor metabolites Transition step The transition step, repeated twice to oxidize two molecules of pyruvate to acetyl-CoA, generates: + 2 NADH + 2 H one precursor metabolite TCA cycle The TCA cycle, repeated twice to incorporate two acetyl groups, generates: 2 ATP by substrate-level phosphorylation (may involve conversion of GTP) + 6 NADH + 6 H 2 FADH2 two different precursor metabolites ©McGraw-Hill Education The Central Metabolic Pathways Glycolysis Converts 1 glucose to 2 pyruvate molecules; net yield = 2 ATP, 2 NADH Investment phase: 2 ATP consumed 2 phosphate groups added Glucose split to two 3-carbon molecules Pay-off phase: 3-carbon molecules converted to pyruvate Generates 4 ATP, 2 NADH ©McGraw-Hill Education ©McGraw-Hill Education  The Central Metabolic Pathways (2) Pentose Phosphate Pathway Breaks down glucose Important in biosynthesis for precursor metabolites Ribose 5-phosphate, erythrose 4-phosphate Also generates variable amount of NADPH Product glyceraldehyde-3-phosphate can enter glycolysis ©McGraw-Hill Education  The Central Metabolic Pathways Transition Step CO2 is removed from pyruvate Electrons transfer to NAD + reducing it to NADH + H + 2-carbon acetyl group joined to coenzyme A to form acetyl- CoA Links previous pathways to TCA cycle ©McGraw-Hill Education  The Central Metabolic Pathways - Figure 6.17 (2) Tricarboxylic Acid (TCA) Cycle Completes oxidation of glucose Produces 2 CO2 2 ATP 6 NADH 2 FADH2 Precursor metabolites ©McGraw-Hill Education ©McGraw-Hill Education  Cellular Respiration Oxidative phosphorylation uses reducing power (NADH, FADH2) generated by glycolysis, transition step, and TCA cycle to synthesize ATP Two processes involved: Electron transport chain uses reducing power of NADH, FADH2 to generate proton motive force ATP synthase uses energy of proton motive force to generate ATP Process proposed by Peter Mitchell in 1961 Initially widely dismissed; he self funded his research Received a Nobel Prize in 1978 for what is now called chemiosmotic theory ©McGraw-Hill Education  The Electron Transport Chain (ETC)—Generating a Proton Motive Force - Figure 6.18 Electron transport chain (ETC) is series of membrane- embedded electron carriers Accepts electrons from NADH, FADH2 Energy released as electrons are passed from one carrier to the next Energy pumps protons across membrane Prokaryotes: cytoplasmic membrane Eukaryotes: inner mitochondrial membrane Creates electrochemical gradient called proton motive force ©McGraw-Hill Education  The Electron Transport Chain (ETC)—Generating a Proton Motive Force - Figure 6.20 ©McGraw-Hill Education Jump to The Electron Transport Chain (ETC)—Generating a Proton Motive Force - Figure 6.20 Long Description  The Electron Transport Chain (ETC)—Generating a Proton Motive Force (1) Components of an Electron Transport Chain Most carriers grouped into large protein complexes that function as proton pumps Other move electrons from one complex to the next Quinones Lipid-soluble; move freely in membrane Can transfer electrons between complexes Cytochromes Contain heme, molecule with iron atom at center Several types; can be used to distinguish bacteria Flavoproteins Proteins to which a flavin is attached FAD, other flavins synthesized from riboflavin ©McGraw-Hill Education  The Electron Transport Chain (ETC)—Generating a Proton Motive Force (2) General Mechanisms of Proton Pumps Some carriers accept only hydrogen atoms (proton-electron pairs), others only electrons Spatial arrangement in membrane shuttles protons to outside of membrane When hydrogen carrier accepts electron from electron carrier, it picks up proton from inside cell (or mitochondrial matrix) When hydrogen carrier passes electrons to electron carrier, protons released to outside of cell (or intermembrane space of mitochondria) Net effect is movement of protons across membrane Establishes concentration gradient Driven by energy released during electron transfer ©McGraw-Hill Education  The Electron Transport Chain (ETC)—Generating a Proton Motive Force (4) Electron Transport Chain of Prokaryotes Tremendous variation: even single species can have several alternate carriers Aerobic respiration in E. coli Can use 2 different NADH dehydrogenases Proton pump equivalent to complex I of mitochondria Succinate dehydrogenase equivalent to complex II of mitochondria Can produce several alternatives to optimally use different energy sources, including H2 Lack equivalents of complex III or cytochrome c Quinones shuttle electrons directly to functional equivalent of complex IV Two versions for high or low O2 concentrations ©McGraw-Hill Education  Membrane-bound Succinate Dehydrogenase ©McGraw-Hill Education  The Electron Transport Chain (ETC)—Generating a Proton Motive Force (5) Anaerobic respiration in E. coli Harvests less energy than aerobic respiration Lower electron affinities of terminal electron acceptors Some components different Can synthesize terminal oxidoreductase that uses nitrate as terminal electron acceptor Produces nitrite E. coli converts to less toxic ammonia Others convert to N2O or N2 Sulfate-reducers use sulfate ( SO 24− ) as terminal electron acceptor Produce hydrogen sulfide as end product ©McGraw-Hill Education  The Electron Transport Chain (ETC)—Generating a Proton Motive Force - Figure 6.20 FADH2 FAD ©McGraw-Hill Education Jump to The Electron Transport Chain (ETC)—Generating a Proton Motive Force - Figure 6.20 Long Description  The Electron Transport Chain (ETC)—Generating a Proton Motive Force (8) ATP Yield of Aerobic Respiration in Prokaryotes Substrate-level phosphorylation: 2 ATP (from glycolysis; net gain) 2 ATP (from the TCA cycle) 4 ATP (total) Oxidative phosphorylation: 6 ATP (from reducing power gained in glycolysis) 6 ATP (from reducing power gained in transition step) 22 ATP (from reducing power gained in TCA cycle) 34 (total) Total ATP gain (theoretical maximum) = 38 ©McGraw-Hill Education  ATP Yield of Aerobic Respiration in Prokaryotes - Figure 6.21 ©McGraw-Hill Education Jump to ATP Yield of Aerobic Respiration in Prokaryotes - Figure 6.21 Long Description  Fermentation - Figure 6.22 Fermentation used when respiration not an option E. coli is facultative anaerobe Aerobic respiration, anaerobic respiration, and fermentation Streptococcus pneumoniae lacks electron transport chain Fermentation only option ATP-generating reactions are only those of glycolysis a) Lactic acid fermentation pathway Additional steps consume excess reducing power + Regenerate NAD b) Ethanol fermentation pathway Jump to Fermentation - Figure 6.22 Long Description ©McGraw-Hill Education  Fermentation Fermentation end products varied; helpful in identification, commercially useful Lactic Acid Ethanol Butyric acid Propionic Acid Mixed Acids 2,3-Butanediol ©McGraw-Hill Education Plate of food, wine & beer, acetone: © Brian Moeskau; cheese: ©Photodisc; both test tube photos: © McGraw-Hill Education/Auburn University Photographic Services  Catabolism of Organic Compounds Other than Glucose Microbes can use variety of compounds Secrete enzymes; transport subunits into cell; degrade further to appropriate precursor metabolites Polysaccharides and disaccharides broken down by amylases, cellulases, disaccharides Glucose enters glycolysis directly; other monosaccharides converted to precursor metabolites Lipids broken down by lipases Glycerol converted to dihydroxyacetone phosphate, enters glycolysis Fatty acids degraded by β ‐ oxidation to enter TCA cycle Proteins broken down by proteases Amino group deaminated; carbon skeletons converted into precursor metabolites ©McGraw-Hill Education  Catabolism of Organic Compounds Other than Glucose ©McGraw-Hill Education  Chemolithotrophs Prokaryotes unique in ability to use reduced inorganic compounds as energy sources Waste products of one organism may serve as energy source for another Hydrogen sulfide (H2S) and ammonia (NH3) Produced by anaerobic respiration when inorganic molecules (sulfate, nitrate) serve as terminal electron acceptors Used as energy sources for sulfur bacteria and nitrifying bacteria ©McGraw-Hill Education  Table 6.7 Metabolism of Chemolithotrophs Common Name Source Oxidation Reaction(s) (Energy Important Feature(s) of Common Genera of Organism of Yielding) Group in Group Energy Hydrogen bacteria H2 H 2 + 1 2 O2 → H 2O Can also use simple organic Hydrogenomonas compounds for energy Sulfur bacteria H2S H 2S + 1 2 O2 → H 2 O + S Some members of this group Acidithiobacillus, (non- can live at a pH of less than 1. Thiobacillus, S + 11 2 O 2 + H 2 O → H 2SO 4 photosynthetic) Beggiatoa, Thiothrix Iron bacteria Reduced 2Fe 2+ + 1 2 O 2 + H 2O Iron oxide present in the Sphaerotilus, Iron → 2Fe3+ + 2OH − sheaths of these bacteria Gallionella ( Fe2+ ) Nitrifying bacteria NH3 NH 3 + 11 2 O 2 → HNO 2 + H 2O Important in the nitrogen cycle Nitrosomonas HNO2 HNO 2 + 1 2 O 2 → HNO3 Important in the nitrogen cycle Nitrobacter ©McGraw-Hill Education  Anabolic Pathways—Synthesizing Subunits from Precursor Molecules (1) Prokaryotes remarkably similar in biosynthesis processes Synthesize subunits using precursor metabolites formed in the central metabolic pathways If enzymes are lacking, end product must be supplied Fastidious bacteria require many growth factors ©McGraw-Hill Education  Anabolic Pathways—Synthesizing Subunits from Precursor Molecules (2) Lipid synthesis requires fatty acids and glycerol Fatty acids: 2-carbon units added to acetyl group from acetyl-CoA Usually 14, 16, or 18 carbon atoms Glycerol: synthesized from dihydroxyacetone phosphate generated during glycolysis ©McGraw-Hill Education  Anabolic Pathways—Synthesizing Subunits from Precursor Molecules - Figure 6.29 Amino Acid Synthesis Synthesis of glutamate provides mechanism for incorporation of nitrogen into organic material ( ) Ammonium NH +4 commonly used via glutamate synthesis Transamination can generate other amino acids ©McGraw-Hill Education  Anabolic Pathways—Synthesizing Subunits from Precursor Molecules - Figure 6.30 Aromatic amino acids: branching pathway Precursors form 7-carbon compound that enters branching pathway Amino acids are feedback inhibitors of enzymes that directs branch to its own synthesis Amino acids also inhibit formation of original 7-carbon compound Result is that cell does not make amino acids that are already present ©McGraw-Hill Education  Anabolic Pathways—Synthesizing Subunits from Precursor Molecules (3) Nucleotide synthesis DNA, RNA initially synthesized as ribonucleotides Purines: atoms added to ribose 5-phosphate to form ring Pyrimidines: ring made, then attached to ribose 5-phosphate ©McGraw-Hill Education  Anabolic Pathways—Synthesizing Subunits from Precursor Molecules - Figure 6.28 Jump to Anabolic Pathways—Synthesizing Subunits from Precursor Molecules - Figure 6.28 Long Description ©McGraw-Hill Education  Lecture 4,5 (Chapter 6) Review (part 2) What are the main functions and elements of the Central Metabolic Pathway (slides 30-31) What is glycolysis? What are the products of glycolysis? What is the difference between glycolysis and the pentose pathway? What is the function of the TCA cycle? What are the final products of the TCA cycle? How does the TCA cycle function in the biosynthesis of amino acids and other compounds? What is the ”transition step” between glycolysis and the TCA cycle? What is oxidative phosphorylation? What does it do? How is the electron transport chain involved? Define proton motive force. What is it used for? What role do extruded protons have in PMF? What is aerobic respiration? Define fermentation What are chemolithotrophs? What are their energy sources? What are anabolic pathways? What are they used for? ©McGraw-Hill Education