Chapter 8 Microbial Metabolism Topics Metabolism Energy Pathways Biosynthesis Catabolism Anabolism Enzymes Metabolism 1 2 Metabolic balancing act Catabolism and anabolism simple model Catabolism Enzymes involved in breakdown of complex organic molecules to extract energy and form simpler end products Anabolism Enzymes involved in the use of energy from catabolism to synthesize macromolecules and cell structures from precursors (simpler products) 3 4 1
Enzymes Function Structure Enzyme-substrate interaction Cofactors Action Regulation Catalysts for chemical reactions Lower the energy of activation Function 5 6 Types of Enzyme (Based on Structure) Conjugated enzymes contain a metallic cofactor, coenzyme, or both, required to function as a catalyst. Simple enzyme protein alone Conjugated enzyme protein and nonprotein Three-dimensional features Enable specificity Active site or catalytic site 7 8 2
Specific active sites (from folding of the enzyme protein ) 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 9 10 Lock-and-key model, and induced fit Cofactors Bind to and activate the enzyme Ex. Metallic cofactors Iron, copper, magnesium Coenzymes 11 12 3
Coenzyme Example: coenzyme transfers chemical groups between substrates Transient carrier - alter a substrate by removing a chemical group from one substrate and adding it to another substrate Ex. vitamins 13 14 Action Exoenzymes Endoenzymes Constitutive Induction or repression Types of reactions Exoenzymes - inactive inside the cell, active after release. Endoenzymes remain in the cell and are active Exoenzymes vs. Endoenzymes 15 16 4
Constitiutive and Regulated enzymes Reaction types Condensation (associated with anabolic reactions) Hydrolysis (associated with catabolic reactions) Transfer reactions Constitutive enzymespresent in constant amounts Regulated enzymes are either induced or repressed. 17 18 enzyme-catalyzed synthesis and hydrolysis reactions Transfer reactions Transfer of electrons from one substrate to another Oxidation (add O 2 to a compound with a loss of electrons, increase charge) Reduction (add e - to a compound, decrease charge) Oxidoreductase Transfer of functional groups from one molecule to another Transferases Aminotransferases 19 20 5
How to remember re-dox? Examples of oxidoreductase, transferase, and hydrolytic enzymes LEO goes GER Losing Electrons is Oxidation Gaining Electrons is Reduction Image from http://library.thinkquest.org 21 22 Enzyme Regulation Metabolic pathways Direct control Genetic control Different metabolic pathways are regulated by the enzymes that catalyze the reactions. Patterns of metabolism 23 24 6
Two common direct control mechanisms- Competitive and Noncompetitive inhibitions Genetic control Repression Induction 25 26 Energy Cell energy model (simplified) Cell energetics Exergonic Endergonic Redox reaction (change in oxidation number) Electron carrier Adenosine Triphosphate (ATP) 27 28 7
Redox Reaction (again) Reduction and oxidation reaction (LEO goes GER): Oxidation: loss of electrons, or gain of oxygen, gives increase in oxidation number. Reduction: gain of electrons, or loss of oxygen, gives decrease in oxidation number. Electron carriers transfer electrons and hydrogens Electron donor Electron acceptor Energy is also transferred and captured by the phosphate in form of ATP Electron carriers Coenzymes Nicotinamide adenine dinucleotide (NAD) Respiratory chain carriers Cytochromes (protein) 29 30 NAD reduction Adenosine Triphosphate (ATP - $$!) Temporary energy repository - energy storage! Break phosphates bonds to release free energy Three part molecule: Nitrogen base 5-carbon sugar (ribose) Chain of phosphates simple annotated 31 32 8
AMP grows to ATP, each stage higher in energy Phosphorylation of glucose by ATP 33 ATP can phosphorylate an organic molecule like glucose during catabolism 34 ATP can be synthesized by substrate-level phosphorylation. Various Pathways Catabolism Embden-Meyerhof-Parnas (EMP) pathway or glycolysis Tricarboxylic acid cycle (TCA) Respiratory chain Aerobic Anaerobic Alternate pathways Fermentation 35 36 9
Metabolism Summary of Glucose and Energy Aerobic respiration (O 2 ) Three stages: Glycolysis Tricarboxylic acid (TCA) Electron transport 37 38 Basics of 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) (cont. next slide) 39 Basic of Glycolysis (continued) Water is generated Net yield of 2 ATPs Final intermediates are two Pyruvic acid molecules (notice that it require 2 different, parallel pathways to finally generate both pyruvic acid molecules ) 40 10
Glycolytic Steps: Metabolism of Glucose to 2 Pyruvic Acid molecules (pyruvate) TCA cycle Each pyruvic acid is processed to enter the TCA cycle (two complete cycles) CO 2 is generated Coenzymes NAD and FAD are reduced to NADH and FADH 2 Net yield of two ATPs Critical intermediates are synthesized 41 42 Electron transport TCA Cycle Steps Each cycle handles one 3 carbon molecule. This means it takes two cycles to burn up one 6 carbon glucose molecule. NADH and FADH 2 donate electrons to the electron carriers Membrane bound carriers transfer electrons (redox reactions) The final electron acceptor completes the terminal step (ex. Oxygen) 43 44 11
Electron Transport (continued) Chemiosmosis and the electron transport system, with oxidative phosphorylation e- transport and formation of a proton gradient Driven by: Chemiosmosis Proton motive force (PMF) 45 46 Electron Transport Chain Locations Eukaryotes mitochondria Prokaryotes Cytoplasmic membrane ATP Yield: One glucose molecule, aerobic respiration 47 48 12
Anaerobic respiration (No O 2 ) Similar to aerobic respiration, except nitrate or nitrite is the final electron acceptor 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 49 50 Types of fermenters Facultative anaerobes Fermentation in the absence of oxygen Respiration in the presence of oxygen Ex. Escherichia coli Strict fermenters No respiration Ex. yeast Products of fermentation Alcoholic fermentation Acidic fermentation Mixed acid fermentation 51 52 13
Fermentation of ethyl alcohol and lactic acid Pyruvate mixed acid fermentation diverse products 53 54 Respiration comparison Biosynthesis Anabolism Amphibolic ( ) Gluconeogenesis Beta oxidation Amination Transamination Deamination Macromolecules 55 56 14
Amphibolic Overview of anabolic and catabolic relationships Integration of the catabolic and anabolic pathways Intermediates serve multiple purposes 57 58 Gluconeogenesis Pyruvate (intermediate) converts to glucose Occurs when the glucose supply is low Beta oxidation Metabolism of fatty acids into acetyl- CoA Krebs (TCA cycle) 4 steps: Oxidation by FAD Hydation of C2=C3 bond Oxidation by NAD + Thiol cleavage at C2-C3 Acetyl-CoA 59 60 15
Production and Conversion of Amino Acids: amination, transamination, deamination Macromolecules Cellular building blocks Monosaccharides Amino acids Fatty acids Nitrogen bases Vitamins 61 62 Photosynthesis free power! Photosynthesis (cont.) 6H2O + 6CO2 C6H12O6+ 6O2 2 independent reactions in the chloroplast 63 64 16