microbial metabolism

• Metabolism


  The sum of all chemical reactions within a living organism
• Catabolism


  Breakdown reactions that release energy
• Anabolism


  Building reactions that consume energy
• Catabolic reaction


  Breakdown of complex organic compounds into simpler ones, and in the process releasing energy
• Catabolic reactions


  • Hydrolytic - utilize water (hydro) & break bonds (lytic)
  • Exergonic - produce more energy than they consume
• Anabolic reaction


  Energy-requiring reactions that involve the building of complex organic molecules from simpler ones
• Anabolic reactions


  • Dehydrating - release water
  • Endergonic - consume more energy than they produce
• Catabolic reactions provide building blocks for anabolic reactions and furnish the energy needed to drive anabolic reactions
• Anabolic reactions are coupled to ATP breakdown, & catabolic reactions are coupled to ATP synthesis
• Enzymes


  Proteins produced by living cells that catalyze chemical reactions by lowering the energy required for a chemical reaction to occur
• Catalysts


  Substances that speed up a chemical reaction without being permanently altered by it
• Lock-and-key model


  Each enzyme acts on a specific substance (substrate) and catalyzes only one reaction
• The enzyme orients the substrate into a position that increases the probability of a reaction
• Enzyme specificity and efficiency


  • Specificity of enzymes is made possible by the unique configuration of each enzyme that enables it to "find" the correct substrate from among the large number of diverse molecules in the cell
• Enzyme names


  • Usually end in "-ase"
  • Prefixes usually include either the reaction it catalyzes or describes its substrate
• Holoenzyme


  Consists of an apoenzyme (protein portion) and a cofactor/coenzyme (non-protein component)
• Coenzyme


  Organic compound (e.g. vitamins)
• Cofactor


  Inorganic compound (e.g. ion)
• Mechanism of enzymatic action


  1. Substrate surface contacts the active site

  2. The intermediate enzyme-substrate complex forms

  3. Substrate molecule is transformed

  4. Products are released from the enzyme
• Factors affecting enzyme activity


  • Temperature
  • pH
  • Substrate concentration
  • Inhibitors
• Temperature


  • Rate of (most) reactions increases as temperature increases
  • Rates are highest at certain optimal temperature beyond which rate of reaction drastically drops
  • The optimal temperature for most bacteria that cause human disease is between 35C and 40C
• Denaturation


  The loss of a protein or enzyme's characteristic 3-D structure causing the loss of structure & function
• pH


  • Most enzymes have an optimum pH at which enzyme activity & reaction rates are characteristically maximal
  • Extreme changes in pH can cause denaturation
• Substrate concentration


  • There is a maximum rate at which a certain amount of enzyme can catalyze a specific reaction
  • Saturation - state where at high substrate concentration, the active site of the enzyme is always occupied
• Enzyme inhibitors

  • Competitive inhibitors - compete with the substrate for the active site
  • Noncompetitive inhibitors - do not compete with the substrate at the active site
• Feedback inhibition


  The end-product of a metabolic pathway inhibits an enzyme's activity at or near the start of the pathway
• Reduction reaction


  Gain of electron (e-) from another molecule
• Oxidation reaction


  Removal of electron (e-) from a molecule, producing energy
• Reduction and oxidation reactions are always coupled (REDOX REACTION)
• Oxidation reaction = release energy = catabolism

  Reduction reaction = lose energy = anabolism
• Dehydrogenation reactions


  In many oxidation reactions, electrons & protons (hydrogen ions, H+) are removed & released at the same time
• Energy production


  Much of the energy released during redox reactions is trapped within the cell by the formation of ATP
• Phosphorylation


  The addition of a phosphate (P) to a chemical compound
• Substrate level phosphorylation


  ATP is usually generated when a high-energy (P) is directly transferred from a phosphorylated compound (substrate) to ADP
• Oxidative phosphorylation


  Electrons are transferred from organic compounds to electron carriers (FAD+ or NAD+), which are then passed through a series of electron carriers (electron transport chain)
• Photophosphorylation


  In photosynthesis, organic molecules are synthesized with the energy of light from the energy-poor building blocks like CO2 and water
• Metabolic pathways


  Series of enzymatically catalyzed chemical reactions that store energy in and release it from organic molecules
• Nutritional classification of organisms by source of energy


  • Phototrophs
  • Chemotrophs
• Nutritional classification of organisms by source of carbon


  • Autotrophs
  • Heterotrophs
• Calvin-Benson cycle


  Three molecules of CO2 are fixed and one molecule of glyceraldehyde 3-phosphate (G3P) is produced and leaves the cycle