Bacterial Metabolism 121

• Metabolism


  Sum of all the biochemical reactions occurring within the living cell required for energy generation and use of energy to synthesize cell materials from small molecules in the environment

  
• Bacterial nutrition


  Substances used in biosynthesis and energy production
• Nutrients required by bacteria

  • Carbon
  • Nitrogen
  • Phosphorous
  • Iron
  • Other molecules
• Bacteria


  • Require energy and nutrients to build proteins and structural membranes and drive biochemical processes
• Sources of energy and electrons for bacteria

  • Carbon source
  • Electron source
  • Energy source
• Lithotrophs


  Organisms that can use reduced inorganic compounds as electron donors
• Organotrophs


  Organisms that can use organic compounds as electron donors
• Types of bacteria based on energy and electron sources

  • Photo-lithotrophs
  • Photo-organotrophs
  • Chemo-lithotrophs
  • Chemo-organotrophs
• Autotroph


  Producers, photosynthetic, use CO2 and H2O, sunlight as energy, make their own food
• Heterotroph


  Require preformed food, digestive and absorptive, most microbes
• Chemoautotroph


  Unique metabolism, use chemical energy from inorganic molecules, Sulfur and Iron
• Fundamental tasks of all cells

  • Synthesize new parts
  • Harvest energy to power reactions
• Energy


  Ability to do work; required to drive various biosynthetic/chemical reactions to do mechanical work
• Catabolism


  Degradation, breaking down complex molecules into simple ones, process that breaks down compound to release energy, generation of energy (ATP)

  
• Anabolism


  Biosynthesis, building complex molecules from simple ones, assemble subunits of macromolecules, use of energy (ATP)

  
• Catabolism and anabolism are intimately linked with each other
• Types of metabolic pathways

  • Linear
  • Branched
  • Cyclical

  
• Substrate


  The substance on which an enzyme acts

  
• Enzyme


  Biological catalyst that speeds up conversion of a substrate into a product

  
• Enzymes increase the rate of chemical reactions, do not become part of the products, are not consumed in the process, and do not create a reaction
• Enzymes are highly specific for substrate(s)

  
• Structures of enzymes


  • Simple enzymes: protein alone
  • Conjugated enzymes (holoenzymes): composed of protein and nonprotein parts
  • Apoenzyme: protein portion of conjugated enzyme (holoenzyme)
  • Cofactors: either organic molecules (Coenzymes) or inorganic elements (metal ions; metallic cofactors)

  
• Substrate-enzyme interaction


  A temporary enzyme-substrate union must occur at the active site, bond formed between the substrate and enzyme are weak and easily reversible, once the enzyme-substrate complex has formed, an appropriate reaction occurs on the substrate, often with the aid of a cofactor, product is formed, enzyme is free to interact with another substrate

  
• Classification of enzymes


  • Prefix or stem word derived from a certain characteristic, usually the substrate acted upon or type of reaction catalyzed
  • Ending -ase
  • Six classes based on biochemical action

  
• Six classes of enzymes

  • Oxidoreductases
  • Transferases
  • Hydrolases
  • Lyases
  • Isomerases
  • Ligases

  
• Enzyme regulation


  Activity of enzymes influenced by the cell's environment (temperature, pH, osmotic pressure), denaturation disrupts the enzyme's shape and prevents the substrate from attaching to the active site

  
• Controls on the actions of enzymes

  • Competitive inhibition
  • Noncompetitive inhibition
• Enzyme actions in E.coli & Enterobacter

  • Inoculation on MacConkey agar plate
• ATP


  Energy is mostly stored as ATP, energy is managed in the form of chemical reactions that involve the making and breaking of bonds and the transfer of electrons
• Reduction


  Gaining of electrons, when a compound gains electrons, it is reduced
• Oxidation


  Losing of electrons, when a compound loses electrons, it is oxidized
• Oxidoreductases


  Enzymes that remove electrons from one substrate and add them to another, their coenzyme carriers are NAD and FAD
• Redox pair


  An electron donor and an electron acceptor involved in a redox reaction
• NAD and FAD


  Coenzymes commonly involved in energy-producing metabolism, NAD is found in mitochondria and derived from niacin, FAD is found in mitochondria and synthesized from riboflavin and two molecules of ATP
• Precursor metabolites


  Intermediates of catabolism that can be used in anabolism, serve as carbon skeletons for building macromolecules
• Metabolic pathways


  • Aerobic respiration
  • Glycolysis
  • Entner-Duodoroff pathway
• Aerobic respiration


  A series of reactions that converts glucose to CO2 and water, allows the cell to recover significant amounts of energy, relies on free oxygen as the final electron and hydrogen acceptor, characteristic of many bacteria, fungi, protozoa, and animals
• Glycolysis


  Converts 1 glucose to 2 pyruvates, yields net 2 ATP, 2 NADH, investment phase uses 2 ATP, pay-off phase produces 4 ATP, 2 NADH total
• Entner-Duodoroff pathway


  An alternate series of reactions that catabolize glucose to pyruvate using a set of enzymes different from those used in glycolysis
• Amino acids


  Alanine, leucine, or valine