microbial metabolism •^•

• Collision theory


  Explains how chemical reactions occur and how certain factors affect the rates of those reactions
• Chemical reactions occur when chemical bonds are formed or broken
• For reactions to take place, atoms, ions, or molecules must collide
• Collision theory


  • All atoms, ions, and molecules are continuously moving and are thus continuously colliding with one another
  • The energy transferred by the particles in the collision can disrupt their electron structures enough to break chemical bonds or form new bonds
• Factors determining if a collision will cause a chemical reaction


  • Velocities of the colliding particles
  • Their energy
  • Their specific chemical configurations
• Higher particle velocities increase the probability of a reaction occurring
• Each chemical reaction requires a specific level of energy
• Even if colliding particles possess the minimum energy needed for reaction, no reaction will take place unless the particles are properly oriented toward each other
• Activation energy


  The amount of energy needed to disrupt the stable electronic configuration of any specific molecule so that the electrons can be rearranged
• Reaction rate


  Depends on the number of reactant molecules at or above the activation energy level
• Ways to increase reaction rate


  • Raise temperature
  • Increase pressure
  • Increase reactant concentration
• Enzymes


  • Can catalyze reactions at rates 10^3 to 10^7 times higher than those of comparable reactions without enzymes
  • Turnover number (maximum number of substrate molecules an enzyme molecule converts to product each second) is generally between 1 and 10,000 and can be as high as 500,000
• Many enzymes exist in the cell in both active and inactive forms
• Prior to 1982, it was believed that only protein molecules had enzymatic activity
• Ribozymes


  • Unique type of RNA that function as catalysts, have active sites that bind to substrates, and are not used up in a chemical reaction
  • Specifically act on strands of RNA by removing sections and splicing together the remaining pieces
• Oxidation-reduction


  Concept related to energy production
• Phosphorylation reactions


  Three types that generate ATP
• Metabolic pathways


  Overall function is to concentrate the energy in nutrient molecules into the bonds of ATP, which serves as a convenient energy carrier
• ATP


  Has "high-energy" or unstable bonds that provide the cell with readily available energy for anabolic reactions
• Metabolic Pathways of Energy Use
• Anabolism


  The production of complex molecules from simpler ones, requiring energy
• Catabolism


  The breakdown of complex molecules into simpler ones, releasing energy
• About 45% of the energy of glucose is lost as heat during complete metabolic oxidation to carbon dioxide and water
• Uses of the remaining energy trapped in ATP


  • Transport of substances across plasma membranes (active transport)
  • Flagellar motion
  • Production of new cellular components
• Autotrophs


  Organisms that build their organic compounds by fixing carbon dioxide in the Calvin-Benson cycle
• Heterotrophs


  Organisms that must have a ready source of organic compounds for biosynthesis
• Polysaccharide biosynthesis


  1. Glucose is phosphorylated to glucose 6-phosphate

  2. Glucose 6-phosphate is converted to adenosine diphospho-glucose (ADPG)

  3. ADPG is linked with similar units to form glycogen
• Lipid biosynthesis


  1. Glycerol portion is derived from dihydroxyacetone phosphate

  2. Fatty acids are built up by adding two-carbon fragments of acetyl CoA
• Roles of lipids


  • Structural components of biological membranes (phospholipids)
  • Energy storage
  • Pigments (carotenoids)
  • Components of chlorophyll
• Amino acid and protein biosynthesis


  1. Some microbes can synthesize all amino acids from glucose and inorganic salts

  2. Amino acids are synthesized by adding an amine group to pyruvic acid or Krebs cycle intermediates (amination)

  3. Amino acids are joined to form proteins by dehydration synthesis
• Purine and pyrimidine biosynthesis


  1. Carbon and nitrogen atoms for purine and pyrimidine rings are derived from amino acids (glycine, glutamine)

  2. Energy for synthesis is provided by ATP
• DNA and RNA are required for protein synthesis
• Nucleotides like ATP, NAD+, and NADP+ play roles in stimulating and inhibiting cellular metabolism