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TORTORA • FUNKE • CASE Microbiology AN INTRODUCTION EIGHTH EDITION B.E Pruitt & Jane J. Stein Chapter 5 Microbial Metabolism PowerPoint® Lecture Slide Presentation prepared by Christine L. Case Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Microbial Metabolism • Metabolism is the sum of the chemical reactions in an organism. • Catabolism is the energy-releasing processes, catabolic, degradative,generally hydrolytic reaction (use water and break chemical bonds). • Exergonic – produce more energy than consume • Anabolism is the energy-using processes, anabolic, biosynthetic, building of complex molecules from simpler ones, involve dehydration synthesis reactions (reactions that release water) • Endergonic – consume more energy that produce. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Microbial Metabolism • Catabolism provides the building blocks and energy for anabolism. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 5.1 ATP stores energy from catabolic reactions and releases it later to drive anabolic reactions and perform other cellular work. The coupling or energy requiring and energy releasing reaction is made possible through the molecule adenosine triphosphate (ATP) Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings ATP • Is made by dehydration synthesis. • Is broken by hydrolysis to liberate useful energy for the cell. When the terminal phosphate group splits from ATP, adenosine diphosphate is formed and energy is released to drive anabolic reactions Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings • A metabolic pathway is a sequence of enzymatically catalyzed chemical reactions in a cell. • Metabolic pathways are determined by enzymes. • Enzymes are proteins encoded by genes. • The collision theory states that chemical reactions can occur when atoms, ions, and molecules collide. • Reaction rate is the frequency of collisions with enough energy to bring about a reaction. • Reaction rate can be increased by enzymes or by increasing temperature or pressure. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Catalyst • Catalyst speeds up a chemical reaction without being permanently altered themselves • Enzymes are biological catalyst, specific for a chemical reaction, acts on a specific substance called a substrate • The enzyme orients the substrate into position that increases the probability of a reaction • Enzyme substrate complex forms by the temporary binding of enzyme and substrate enable the collison to be more effective and lowers the activation energy of the reaction Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Enzymes •Apoenzyme: protein portion of an enzyme, can be the whole enzyme •Cofactor: Nonprotein component, help catalyze by forming a bridge between the enzyme and the substrate •Coenzyme: Organic cofactor, NAD+NADP+FAD Coenzyme A, may assist the enzymatic reaction by accepting atoms removed from the substrate or by donating atoms required by the substrate, electron carriers •Holoenzyme: Apoenzyme + cofactor (coenzyme) Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 5.3 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Enzyme Classification 6 classes, named for type of chemical reaction they catalyze • Oxidoreductase Oxidation-reduction reactions • Transferase Transfer functional groups • Hydrolase Hydrolysis • Lyase Removal of atoms without hydrolysis • Isomerase Rearrangement of atoms • Ligase Joining of molecules, uses ATP Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Factors Influencing Enzyme Activity • Enzymes can be denatured by temperature and pH Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 5.6 Factors Influencing Enzyme Activity • Temperature Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings pH Figure 5.5a Factors Influencing Enzyme Activity • Competitive inhibition – inhibitors fill the active site of an enzyme and compete with the normal substrate for the active site Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 5.7a, b Factors Influencing Enzyme Activity Ex – PABA is an essential nutrient of many bacteria in the synthesis of folic acid. Sulfanilamide binds to the enzyme that converts PABA to folic acid, bacteria cannot grow Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Factors Influencing Enzyme Activity • Noncompetitive inhibition- inhibitor interacts with another part of the enzyme • Allosteric inhibitor –inhibitor binds to a site other than the substrate binding site and cause the active site to change shape making it non-functional Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 5.7a, c Factors Influencing Enzyme Activity • Feedback inhibition – a series of enzymes make an end product that inhibits the first enzyme in the series, this shuts down the entire pathway when sufficient end product has been made Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 5.8 Energy Production • Nutrient molecules have energy associated with electrons that form bonds between their atoms • Reactions in catabolic pathways convert this energy into bonds of ATP, which serves as a convenient energy carrier Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Oxidation-Reduction • Oxidation is the removal of electrons. • Reduction is the gain of electrons. • Redox reaction is an oxidation reaction paired with a reduction reaction. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 5.9 Oxidation-Reduction • In biological systems, the electrons are often associated with hydrogen atoms. Biological oxidations are often dehydrogenations. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 5.10 Energy Production • Cells use redox reactions in catabolism to extract energy from nutrient molecules • Cells take nutrients, degrade them from a highly reduced compound with a lot of hydrogen atoms to a highly oxidized compound which can serve as an energy source • Ex – a cell oxidizes a molecule of glucose C6H12C6 to CO2 and H2O, the energy in glucose is removed in a stepwise manner and ultimately trapped by ATP Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings • To produce energy from glucose microbes use two general processes • Cellular respiration • Fermentation • Both start with glycolysis but follow different subsequent pathways Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings The Generation of ATP • ATP is generated by the phosphorylation of ADP. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Carbohydrate Catabolism • Most organisms oxidize carbohydrates as their primary source of cellular energy, most common is glucose • The breakdown of carbohydrates to release energy • Glycolysis • Krebs cycle • Electron transport chain Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Glycolysis • The oxidation of glucose to pyruvic acid, produces ATP and NADH. 6-carbon sugar is split into 2 3carbon sugars, the sugar is oxidized, releasing energy and their atoms rearrange to form 2 molecules of pyruvic acid Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 1 - 6 carbon sugar 2 - 3 carbon sugars Preparatory Stage Preparatory Stage Glucose 1 Glucose 6-phosphate • 2 ATPs are used 2 • Glucose is split to form 2 Glucose-3phosphate Fructose 6-phosphate 3 4 Fructose 1,6-diphosphate 5 Dihydroxyacetone phosphate (DHAP) Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Glyceraldehyde 3-phosphate (GP) Figure 5.12.1 Energy-Conserving Stage • 2 Glucose-3phosphate oxidized to 2 Pyruvic acid • 4 ATP produced 6 1,3-diphosphoglyceric acid 7 • 2 NADH produced • Net 2 ATP 3-phosphoglyceric acid 8 2-phosphoglyceric acid 9 Phosphoenolpyruvic acid (PEP) 10 Pyruvic acid Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 5.12.2 Pyruvic Acid • Pyruvic acid can be channeled into the next step of either fermentation of cellular respiration Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Alternatives to Glycolysis • Pentose phosphate pathway: • Uses pentoses and NADPH • Operates with glycolysis • Entner-Doudoroff pathway: • Produces NADPH and ATP • Does not involve glycolysis • Pseudomonas, Rhizobium, Agrobacterium Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Cellular Respiration • ATP generating process in which molecules are oxidized and the final electron acceptor is almost always an inorganic molecule Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Intermediate Step •Pyruvic acid (from glycolysis) cannot enter the Krebs cycle directly •In a preparatory step it most lose one molecule of CO2 and becomes a two carbon compound (decarboyxlated) •The 2c-carbon complex – acetyl group attaches to coenzyme A through a high energy bond •Result is acetyl-coenzyme A, 2 acetyl-CoA per glucose Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Krebs Cycle – TCA cycle – Citric Acid Cycle • Series of redox reactions that transfer potential energy in the form of electrons to electron carriers, chiefly NAD • For every AcetylCoA – 2 ATP, 4 CO2, 6 NADH, 2 FADH Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings The Electron Transport Chain • A series of carrier molecules that are, in turn, oxidized and reduced as electrons are passed down the chain. • Series of reductions that indirectly transfer the energy stored in the coenzymes formed in the Krebs cycle to ATP Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Respiration • Aerobic respiration: The final electron acceptor in the electron transport chain is molecular oxygen (O2). • In prokaryotes – results in 38 ATP • In eukaryotes – results in 36 ATP, lose energy shuttling electrons across mitochondria membrane • Anaerobic respiration: The final electron acceptor in the electron transport chain is not O2. Yields less energy than aerobic respiration because only part of the Krebs cycles operations under anaerobic conditions. • ATP levels vary with the organism and the pathway, not all carrier in the electron transport chain are used Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Pathway Eukaryote Prokaryote Glycolysis Cytoplasm Cytoplasm Intermediate step Cytoplasm Cytoplasm Krebs cycle Mitochondrial matrix Cytoplasm ETC Mitochondrial inner membrane Plasma membrane Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Fermentation • Glucose can be converted to another organic product in fermentation • Releases energy from oxidation of organic molecules • Does not require oxygen • Does not use the Krebs cycle or ETC • Uses an organic molecule as the final electron acceptor • Produces only a small amount of ATP Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Fermentation Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 5.18b Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Other Energy Sources • Microbes can oxidize lipids and proteins for energy • Lipids are broken down by lipases which break fats down into fatty acids and glycerol components. Each component is then metabolized separately • Beneficial for oil spills Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Lipid Catabolism Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 5.20 • Proteins are broken down by proteases and peptidases which break down proteins to amino acids and then convert them by deamination,(removal of the amino group, to enter the Krebs cycle. The amino group is converted to an ammonia ion which can be excreted from the cell. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Protein Catabolism Protein Extracellular proteases Deamination, decarboxylation, dehydrogenation Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Amino acids Organic acid Krebs cycle Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Biochemical tests • Used to identify bacteria. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Photosynthesis • Photo: Conversion of light energy into chemical energy (ATP) • Synthesis: Fixing carbon into organic molecules • Photosynthesis – synthesis of complex organic compounds from single inorganic substances Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Photosynthesis • Conversion of light energy from the sun into chemical energy • Chemical energy is used to convert CO2 from atmosphere to more reduced carbon compounds, primarily sugars • Synthesis of sugar by using carbon atoms from CO2 gas is call carbon fixation • In photosynthesis electrons are taken from hydrogen atoms of water, an energy poor molecule, and incorporated into sugar, an energy rich molecule Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings •Species that use light energy are phototrophs. •Species that obtain energy from chemicals in their environment are chemotrophs. •Organisms that need only CO2 as a carbon source are autotrophs. •Organisms that require at least one organic nutrient as a carbon source are heterotrophs. •These categories of energy source and carbon source can be combined to group prokaryotes according to four major modes of nutrition. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings • Photoautotrophs are photosynthetic organisms that harness light energy to drive the synthesis of organic compounds from carbon dioxide. • Chemoautotrophs need only CO2 as a carbon source, but they obtain energy by oxidizing inorganic substances, rather than light. • These substances include hydrogen sulfide (H2S), ammonia (NH3), and ferrous ions (Fe2+) among others. • This nutritional mode is unique to prokaryotes. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings •Photoheterotrophs use light to generate ATP but obtain their carbon in organic form. •This mode is restricted to prokaryotes. •Chemoheterotrophs must consume organic molecules for both energy and carbon. •This nutritional mode is found widely in prokaryotes, protists, fungi, animals, and even some parasitic plants. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Metabolic Diversity Among Organisms Nutritional type Energy source Carbon source Example Photoautotroph Light CO2 Oxygenic: Cyanobacteria plants. Anoxygenic: Green, purple bacteria. Photoheterotroph Light Organic compounds Green, purple nonsulfur bacteria. Chemoautotroph Chemical CO2 Iron-oxidizing bacteria. Organic compounds Fermentative bacteria. Animals, protozoa, fungi, bacteria. Chemoheterotroph Chemical Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Amphibolic pathways • Are metabolic pathways that have both catabolic and anabolic functions. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 5.32.1 Amphibolic pathways Most of the ATP made by the cell is used in the production of new cellular components Amphibolic pathways bridge the reactions that lead to the breakdown and synthesis of carbohydrates, lipids, proteins and nucleus. These pathways allow for the simultaneous reactions to occur in which the breakdown products formed in one reaction are used in another reaction to synthesize a different compound, or vice versa Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 5.32.2