Lecture 5. Microbial Metabolism PDF

Microbial Metabolism Sheena V. Borjal Contents 1. Microbial nutrients & Nutrient Uptake 2. Energetics, Enzymes, and Redox 3. Catabolism: Fermentation & Respiration 4. Biosyntheses Metabolism is the series of biochemical reactions by which the cell breaks down or biosynthesizes various...

Microbial Metabolism Sheena V. Borjal Contents 1. Microbial nutrients & Nutrient Uptake 2. Energetics, Enzymes, and Redox 3. Catabolism: Fermentation & Respiration 4. Biosyntheses Metabolism is the series of biochemical reactions by which the cell breaks down or biosynthesizes various metabolites. Microbial Nutrients & Nutrient Uptake: Cell Nutrition Macronutrients: required in large amounts Micronutrients: required in minute amounts Chemical Makeup of a Cell Microbial Nutrients & Nutrient Uptake: Cell Nutrition C: needed in the largest amount (50% of a cell’s dry weight) O & H: combined, 25% of dry weight N: 13% of dry weight P,S,K,Mg, & Se: combined, less than 5% of dry weight Microbial Nutrients & Nutrient Uptake: Cell Nutrition Microbial Nutrients & Nutrient Uptake: Cell Nutrition Microbial Nutrients & Nutrient Uptake: Transport of Nutrients Microbial Nutrients & Nutrient Uptake: Transport of Nutrients SIMPLE TRANSPORT reactions are driven by the energy inherent in the proton motive force. SYMPORT: solute and proton are cotransported in one direction ANTIPORT: solute and proton are transported in opposite direction Microbial Nutrients & Nutrient Uptake: Transport of Nutrients GROUP TRANSLOCATION 1. the transported substance is chemically modified during the transport process; 2. an energy- rich organic compound drives the transport event Microbial Nutrients & Nutrient Uptake: Transport of Nutrients GROUP TRANSLOCATION PHOSPHOTRANSFERASE SYSTEM: a family of five proteins that work in concert to trasnport any given sugar. Microbial Nutrients & Nutrient Uptake: Transport of Nutrients ABC TRANSPORT SYSTEM “ATP- binding cassette” Transport system that employ a periplasmic binding protein along with transmembrane and ATP- hydrolyzing components Energetics, Enzymes, and Redox: Energy Classes of Microbes Energy- yielding reactions are part of metabolism called catabolism. Energetics, Enzymes, and Redox: Catalysis and Enzymes Activation energy is the minimum energy required for a chemical reaction to begin. Energetics, Enzymes, and Redox: Catalysis and Enzymes Catalysts function by lowering the activation energy of a reaction, thereby increasing the reaction rate Energetics, Enzymes, and Redox: Catalysis and Enzymes Enzymes are major catalysts in cells. The are proteins that are highly specific for the reactions they catalyze. Energetics, Enzymes, and Redox: Electron Donors & Acceptors Redox reaction occurs in pairs. Electron donor: the substance that is oxidized Electron acceptor: the substance that is reduced Energetics, Enzymes, and Redox: Energy- Rich Compounds Catabolism: Fermentation & Respiration Fermentation: a form of anaerobic catabolism in which organic compounds both donate & accept electrons. Respiration: a form of aerobic or anaerobic catabolism in which an organic or inorganic electron donor is oxidized with oxygen or some other compound functioning as electron acceptor Catabolism: Fermentation & Respiration Glycolysis & Fermentation Energetics, Enzymes, and Redox: Catabolism: Fermentation & Respiration Glycolysis & Fermentation Catabolism: Fermentation & Respiration Fermentative Diversity Sugars such as glucose & other hexoses as well as disaccharides & other relatively small sugars are preeminently fermentable. Since glucose is needed for glycolysis, sugars other than glucose must first be converted to glucose by isomerase enzymes. Different types of fermentations are classified by either the substrate fermented or the products formed. Catabolism: Fermentation & Respiration Fermentative Diversity Catabolism: Fermentation & Respiration Benefits of Fermentation During glycolysis, glucose is consumed, ATP is made, & fermentation products are generated. For the organism, the crucial product is ATP, fermentation products being merely waste products that must be discarded. These fermentation products are important to humans. Catabolism: Fermentation & Respiration Benefits of Fermentation During glycolysis, glucose is consumed, ATP is made, & fermentation products are generated. For the organism, the crucial product is ATP, fermentation products being merely waste products that must be discarded. These fermentation products are important to humans. Catabolism: Fermentation & Respiration The Citric Acid Cycle Catabolism: Fermentation & Respiration The Citric Acid Cycle Catabolism: Fermentation & Respiration The Glyoxylate Cycle Catabolism: Fermentation & Respiration Options for Energy Conservation Anaerobic Respiration: electron acceptors other than oxygen support respiration Chemolitotrophs: use inorganic compounds as electron donors Phototrophs: light energy is used instead of a chemical to drive electron flow & generate a proton motive force Biosyntheses Anabolism: process of synthesizing complex molecules from simpler ones Biosyntheses Pentose Phosphate Pathway  Summary Cells are primarily composed of elements H,O, C, N, P, & S. Nutrients required by a cell in large amounts are called macronutrients while those required in very small amounts, such as trace elements or growth factors, are micronutrients. Proteins are the most abundant class of macromolecules in the cell. The active transport of nutrients into the cell is an energy- requiring process driven by ATP (or some other energy-rich compound) or by the proton motive force. At least three classes of transport systems are known: simple, group translocation, and ABC systems. Each functions to accumulate solutes against the concentration gradient.  Summary All microorganisms conserve energy from either the oxidation of chemicals or from light. Chemoorganotrophs use organic chemicals as their electron donors, while chemolithotrophs use inorganic chemicals. Phototrophic organisms convert light energy into chemical energy (ATP) and include both oxygenic and anoxygenic species. Enzymes are protein catalysts that increase the rate of bio- chemical reactions by activating the substrates that bind to their active site. Enzymes are highly specific in the reactions they catalyze, and this specificity resides in the three-dimensional structures of the polypeptide(s) that make up the protein(s). Oxidation–reduction reactions require electron donors and electron acceptors. The energy released in redox reactions is conserved in compounds that contain energy-rich phosphate or sulfur bonds.  Summary The most common of these compounds is ATP, the prime energy carrier in the cell. The glycolytic pathway is used to break down glucose to pyruvate and is a widespread mechanism for energy conservation by fermentative anaerobes that employ substrate-level phosphorylation. The citric acid cycle generates CO2 and electrons for the electron transport chain and is also a source of biosynthetic intermediates. The glyoxylate cycle is necessary for the catabolism of two-carbon electron donors, such as acetate. Polysaccharides are important structural components of cells and are biosynthesized from activated forms of their monomers. Gluconeogenesis is the production of glucose from nonsugar precursors.  References Kumar, Surinder. (2016). Essentials of Microbiology. Jaypee Brothers Medical Publishers (P) Ltd. Madigan, M. T., Bender, K. S., Buckley, D. H., Sattley, W. M., and Stahl, D.A. (2019). Brock Biology of Microorganisms. Pearson Education Limited. Urry, Lisa A., Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, and Rebecca B. Orr. (2021). Campbell Biology. Pearson Education Limited.