Microbio

• Chemolithotrophs


  Prokaryotes that can tap the energy available from the oxidation of inorganic compounds
• Inorganic compounds that can be oxidized by chemolithotrophs

  • H2
  • H2S (hydrogen sulfide)
  • NH3 (ammonia)
  • Fe2+ (ferrous iron)
• Chemolithotrophy occurs only in prokaryotes and is widely distributed among species of Bacteria and Archaea
• Phototrophy


  Using light as an energy source
• Forms of phototrophy


  • Oxygenic photosynthesis
  • Anoxygenic phototrophy
• Heterotrophs


  Organisms that use organic carbon as their carbon source
• Autotrophs


  Organisms that use inorganic carbon (CO2) as their carbon source
• Autotrophs are primary producers because they can synthesize organic compounds from CO2</b>
• Most organic matter on Earth has been produced by phototrophs
• Some microbial habitats are too extreme for most organisms to survive, being too hot or too salty
• Metabolism


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


  Energy-releasing reactions that break down complex molecules into simpler ones
• Anabolic reactions


  Energy-requiring reactions that build larger molecules from smaller ones
• When complex molecules are split apart (catabolism)


  Some of the energy is transferred to and trapped in ATP, and the rest is given off as heat
• When simple molecules are combined to form complex molecules (anabolism)


  ATP provides the energy for synthesis, and again some energy is given off as heat
• Free energy (G)


  The energy available to do work
• Exergonic reactions


  Reactions that release free energy
• Endergonic reactions


  Reactions that require free energy
• Activation energy


  The energy required to start a chemical reaction, even if it is exergonic
• Catalysts such as enzymes lower the required activation energy
• Enzymes


  • They can catalyze reactions at rates 108 to 1010 times higher than those of comparable reactions without enzymes
  • They have a turnover number (maximum number of substrate molecules an enzyme molecule converts to product each second) generally between 1 and 10,000, and can be as high as 500,000
• Apoenzyme


  The protein portion of an enzyme
• Cofactor


  A nonprotein component that is required for an enzyme to be active
• Coenzyme


  A cofactor that is an organic molecule
• Important coenzymes


  • Nicotinamide adenine dinucleotide (NAD+)
  • Nicotinamide adenine dinucleotide phosphate (NADP+)
  • Flavin mononucleotide (FMN)
  • Flavin adenine dinucleotide (FAD)
  • Coenzyme A
• Nicotinamide adenine dinucleotide (NAD+)


  One of the most important coenzymes in cellular metabolism, contains derivatives of the B vitamin niacin (nicotinic acid) and functions as an electron carrier
• Nicotinamide adenine dinucleotide phosphate (NADP+)


  One of the most important coenzymes in cellular metabolism, contains derivatives of the B vitamin niacin (nicotinic acid) and functions as an electron carrier, primarily involved in anabolic (energy-requiring) reactions
• Flavin coenzymes (FMN and FAD)


  Contain derivatives of the B vitamin riboflavin and are also electron carriers
• Coenzyme A (CoA)


  Contains a derivative of pantothenic acid, another B vitamin, and plays an important role in the synthesis and breakdown of fats and in the Krebs cycle
• Coenzymes may assist enzymes by accepting atoms removed from the substrate or by donating atoms required by the substrate. Some coenzymes act as electron carriers.
• Many coenzymes are derived from vitamins.
• Apoenzymes are inactive by themselves and must be activated by cofactors. Together, the apoenzyme and cofactor form a holoenzyme, or whole, active enzyme.
• If the cofactor is removed, the apoenzyme will not function.
• Nicotinamide adenine dinucleotide (NAD+)


  One of the most important coenzymes in cellular metabolism, functions as an electron carrier, primarily involved in catabolic (energy-yielding) reactions
• Nicotinamide adenine dinucleotide phosphate (NADP+)


  One of the most important coenzymes in cellular metabolism, functions as an electron carrier, primarily involved in anabolic (energy-requiring) reactions
• Flavin coenzymes (FMN, FAD)


  Contain derivatives of the B vitamin riboflavin and are also electron carriers
• Coenzyme A (CoA)


  Contains a derivative of pantothenic acid, plays an important role in the synthesis and breakdown of fats and in the Krebs cycle
• Holoenzyme


  • Consists of an apoenzyme (protein portion) and a cofactor (nonprotein portion)
  • The cofactor can be a metal ion or an organic molecule called a coenzyme
• Enzyme-substrate complex


  Lowers the activation energy of the reaction
• Chemical reactions require increased activation energy without an enzyme as a biological catalyst