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Microbiology: A Systems Approach
PowerPoint to accompany Microbiology: A Systems Approach Cowan/Talaro Chapter 8 Microbial Metabolism Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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Chapter 8 Topics Metabolism Energy Pathways Biosynthesis
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Metabolism Catabolism Anabolism Enzymes
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Catabolism Enzymes are involved in the breakdown of complex organic molecules in order to extract energy and form simpler end products
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Anabolism Enzymes are involved in the use of energy from catabolism in order to synthesize macromolecules and cell structures from precursors (simpler products)
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The relationship between catabolism and anabolism.
Fig. 8.1 Simplified model of metabolism
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Enzymes Function Structure Enzyme-substrate interaction Cofactors
Regulation
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Function Catalysts for chemical reactions
Lower the energy of activation
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Structure Simple enzyme Conjugated enzyme Three-dimensional features
protein alone Conjugated enzyme protein and nonprotein Three-dimensional features Enable specificity Active site or catalytic site
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Conjugated enzymes contain a metallic cofactor, coenzyme, or both in order for it to function as a catalyst. Fig. 8.2 Conjugated enzyme structure
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Specific active sites (amino acids) arise due to the folding of the protein (enzyme).
Fig. 8.3 How the active site and specificity of the apoenzyme arise.
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Enzyme-substrate interactions
Substrates specifically bind to the active sites on the enzyme “lock-and-key” Induced fit Once the reaction is complete, the product is released and the enzyme reused
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An example of the “lock-and-key” model, and the induced fit model.
Fig. 8.4 Enzyme-substrate reactions
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Cofactors Bind to and activate the enzyme Ex. Metallic cofactors
Iron, copper, magnesium Coenzymes
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Coenzyme Transient carrier - alter a substrate by removing a chemical group from one substrate and adding it to another substrate Ex. vitamins
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An example of how a coenzyme transfers chemical groups from one substrate to another.
Fig. 8.5 The carrier functions of coenzymes
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Action Exoenzymes Endoenzymes Constitutive Induction or repression
Types of reactions
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Exoenzymes are inactive while inside the cell, but upon release from the cell they become active. In contrast, endoenzymes remain in the cell and are active. Fig. 8.6 Types of enzymes, as described by their location of action.
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Constitutive enzymes are present in constant amounts, while regulated enzymes are either induced or repressed. Fig. 8.7 Constitutive and regulated enzymes
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Types of Reaction Condensation Hydrolysis Transfer reactions
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Condensation reactions are associated with anabolic reactions, and hydrolysis reactions are associated with catabolic reactions. Fig. 8.8 Examples of enzyme-catalyzed synthesis and hydrolysis reactions
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Transfer reactions Transfer of electrons from one substrate to another
Oxidation and reduction Oxidoreductase Transfer of functional groups from one molecule to another Transferases Aminotransferases
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Examples of oxidoreductase, transferase, and hydrolytic enzymes.
Table 8.A A sampling of enzymes, their substrates, and their reactions
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Regulation Metabolic pathways Direct control Genetic control
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The different metabolic pathways are regulated by the enzymes that catalyze the reactions.
Fig.8.9 Patterns of metabolism
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Competitive inhibition and noncompetitive inhibition are examples of direct control (regulation) of the action of the enzymes. Fig Examples of two common control mechanisms for enzymes.
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Genetic control Repression Induction
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Repression is when end products can stop the expression of genes that encode for proteins (enzymes) which are responsible for metabolic reactions. Fig One type of genetic control of enzyme synthesis
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Summary of major enzyme characteristics.
Table 8.1 Checklist of enzyme characteristics
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Energy Cell energetics Redox reaction Electron carrier
Exergonic Endergonic Redox reaction Electron carrier Adenosine Triphosphate (ATP)
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The general scheme associated with metabolism of organic molecules, the redox reaction, and the capture of energy in the form of ATP. Fig A simplified model that summarizes the cell’s energy machine.
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Redox reaction Reduction and oxidation reaction
Electron carriers transfer electrons and hydrogens Electron donor Electron acceptor Energy is also transferred and captured by the phosphate in form of ATP
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Electron carriers Coenzymes Respiratory chain carriers
Nicotinamide adenine dinucleotide (NAD) Respiratory chain carriers Cytochromes (protein)
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Electron carriers, such as NAD, accept electrons and hydrogens from the substrate (organic molecule). Fig Details of NAD reduction
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Adenosine Triphosphate (ATP)
Temporary energy repository Breaking of phosphates bonds will release free energy Three part molecule Nitrogen base 5-carbon sugar (ribose) Chain of phosphates
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The phosphates capture the energy and becomes part of the ATP molecule.
Fig The structure of adenosine triphosphate and its partner compounds, ADP and AMP.
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ATP can be used to phosphorylate an organic molecule such as glucose during catabolism.
Fig An example of phosphorylation of glucose by ATP
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ATP can be synthesized by substrate-level phosphorylation.
Fig ATP formation by substrate-level phosphorylation
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Pathways Catabolism Embden-Meyerhof-Parnas (EMP) pathway or glycolysis
Tricarboxylic acid cycle (TCA) Respiratory chain Aerobic Anaerobic Alternate pathways Fermentation
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A summary of the metabolism of glucose and the synthesis of energy.
Fig Overview of the flow, location, and products of Pathways in aerobic respiration.
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Aerobic respiration Glycolysis Tricarboxylic acid (TCA)
Electron transport
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Glycolysis Oxidation of glucose
Phosphorylation of some intermediates (Uses two ATPs) Splits a 6 carbon sugar into two 3 carbon molecules Coenzyme NAD is reduced to NADH Substrate-level-phosphorylation (Four ATPs are synthesized)
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Glycolysis continued Water is generated Net yield of 2 ATPs
Final intermediates are two Pyruvic acid molecules
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The glycolytic steps associated with the metabolism of glucose to pyruvic acid (pyruvate).
Fig Summary of glycolysis
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TCA cycle Each pyruvic acid is processed to enter the TCA cycle (two complete cycles) CO2 is generated Coenzymes NAD and FAD are reduced to NADH and FADH2 Net yield of two ATPs Critical intermediates are synthesized
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The steps associated with TCA cycle.
Fig The reaction of a single turn of the TCA cycle
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Electron transport NADH and FADH2 donate electrons to the electron carriers Membrane bound carriers transfer electrons (redox reactions) The final electron acceptor completes the terminal step (ex. Oxygen)
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Electron transport continued
Chemiosmosis Proton motive force (PMF)
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Chemiosmosis entails the electron transport and formation of a proton gradient (proton motive force). Fig The electron transport system and oxidative phosphorylation
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Electron transport chain
Mitochondria eucaryotes Cytoplasmic membrane procaryotes
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Total yield of ATP for one glucose molecule from aerobic respiration.
Table 8.4 Summary of aerobic respiration for one glucose molecule
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Anaerobic respiration
Similar to aerobic respiration, except nitrate or nitrite is the final electron acceptor
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Fermentation Glycolysis only
NADH from glycolysis is used to reduce the organic products Organic compounds as the final electron acceptors ATP yields are small (per glucose molecule), compared to respiration Must metabolize large amounts of glucose to produce equivalent respiratory ATPs
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The fermentation of ethyl alcohol and lactic acid.
Fig The chemistry of fermentation systems
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Types of fermenters Facultative anaerobes Strict fermenters
Fermentation in the absence of oxygen Respiration in the presence of oxygen Ex. Escherichia coli Strict fermenters No respiration Ex. yeast
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Products of fermentation
Alcoholic fermentation Acidic fermentation Mixed acid fermentation
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An example of mixed acid fermentation and the diverse products synthesized.
Fig Miscellaneous products of pyruvate
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Biosynthesis Anabolism Amphibolic Gluconeogenesis Beta oxidation
Amination Transamination Deamination Macromolecules
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Amphibolic Integration of the catabolic and anabolic pathways
Intermediates serve multiple purposes
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Intermediates can serve to synthesize amino acids, carbohydrates and lipids.
Fig An amphibolic view of metabolism
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Gluconeogenesis Pyruvate (intermediate) is converted to glucose
Occurs when the glucose supply is low
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Beta oxidation Metabolism of fats into acetyl, which can then enter the TCA cycle as acetyl CoA.
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Examples of amination, transamination, and deamination.
Fig Reactions that produce and convert amino acids
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Macromolecules Cellular building blocks Monosaccharides Amino acids
Fatty acids Nitrogen bases Vitamins
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