Metabolism

• Metabolism


  All of the biological reactions that occur within an organism
• Metabolism

  1. Catabolism

  2. Anabolism
• Catabolism


  Reactions that provide useable energy (e.g. ATP)
• Anabolism


  Reactions that build the molecules that make up cells and extracellular matrix
• Cells "fund" anabolic reactions by combining them with catabolic reactions
• If there are no catabolic reactions nearby, cells "bank" energy by storing it as ATP (or similar molecules)
• Electron carriers

  Act as both electron acceptors and electron donors in metabolism, accepting electrons from the fuel and passing them to the final electron acceptor
• Major soluble electron carriers

  • NAD+/NADH
  • NADP+/NADPH
  • FAD/FADH2
• Organic nutrients

  • Amino acids
  • Coenzymes
  • Vitamins
• Inorganic nutrients - Macronutrients

  • Carbon
  • Oxygen
  • Nitrogen
  • Sulfur
  • Phosphorus
  • Hydrogen
  • Potassium
  • Calcium
• Inorganic nutrients - Micronutrients


  • Zinc
  • Copper
  • Manganese
• If you can't make your own carbon, heterotrophy is fine
• Little changes + trillions of microbes = big changes
• Redox potential


  Ability to "bank" electrons and pass them to other molecules
• Oxidation of fuel


  Electrons move from fuel molecule to electron acceptor like O2
• Electron carriers

  Act as both electron acceptors and electron donors in metabolism, accepting electrons from fuel and passing them to final electron acceptor
• Major soluble electron carriers

  • NAD+/NADH
  • NADP+/NADPH
  • FAD/FADH2
• Membrane-bound electron carriers


  • Important in electron transport chain for oxidative phosphorylation
• Oxidative phosphorylation

  1. Electrons from NADH and FADH2 transferred to O2, releasing energy

  2. Energy captured as proton gradient (proton motive force)

  3. Flow of protons down gradient results in phosphorylation of ADP by ATP synthase

  
• Electron transport chain


  Where oxidative phosphorylation occurs
• Substrate-level phosphorylation

  Occurs in glycolysis and Krebs cycle, phosphate transferred from organic molecule to ADP
• Oxidative phosphorylation


  Inorganic phosphate added to ADP due to electron transport and proton gradient
• No electron transport chain or proton motive force means no oxidative phosphorylation, only substrate-level phosphorylation
• Proton motive force (PMF)

  Energy captured in the form of a proton gradient across the plasma membrane
• The H+ concentration is higher outside of the cell than it is inside the cytoplasm
• The cytoplasm has a slightly negative charge compared to the outside of the cell
• Flow of protons down their electrochemical gradient (across the plasma membrane back into the cytoplasm)


  Results in phosphorylation of ADP
• ATP synthase

  Enzyme that catalyzes the phosphorylation of ADP
• Oxidative phosphorylation


  Occurs via the electron transport chain
• Substrate-level phosphorylation

  Occurs in glycolysis and Krebs cycle; phosphate is transferred from an organic molecule to ADP
• Oxidative phosphorylation


  Occurs as a result of electron transport and proton gradient; inorganic phosphate is added to ADP
• Substrate-level phosphorylation does not require an electron transport chain or proton motive force
• The maximum theoretical energy yield from aerobic respiration is 32 molecules of ATP
• Fermentation

  1. Stage 1: Glycolysis (oxidation of glucose to pyruvate)

  2. Stage 2: Pyruvate reduced to alcohol/acid and NADH oxidized to NAD+
• Fermentation


  Redox reaction that produces NAD+ so glycolysis can continue making 2 ATPs
• Anaerobic respiration is exactly the same as aerobic respiration, except the final electron acceptor is not oxygen
• Many microbes are anaerobic and use alternative electron acceptors
• Alternative electron acceptors

  • NO2-
  • NO3-
• Sugars are not the only biomolecules that can be catabolized for energy
• Proteins are broken into amino acids by proteases, then deaminated. The resulting molecules can enter the TCA cycle