metabolism and nutrition

• Metabolism


  All of the chemical reactions that occur in the body
• Catabolism


  Chemical reactions that break down complex organic molecules into simpler ones
• Anabolism


  Chemical reactions that combine simple molecules and monomers to form the body's complex structural and functional components
• ATP


  The "energy currency" of a living cell that participates most often in energy exchanges
• Coupling of catabolism and anabolism by ATP

  1. ATP is spent and earned over and over to drive cellular activities

  2. ATP couples energy-releasing catabolic reactions to energy-requiring anabolic reactions
• Oxidation


  The removal of electrons from an atom or molecule, resulting in a decrease in potential energy
• Reduction


  The addition of electrons to a molecule, resulting in an increase in potential energy
• Oxidation-reduction (redox) reactions


  Paired reactions where one substance is oxidized and another is simultaneously reduced
• Phosphorylation


  The addition of a phosphate group to a molecule, increasing its potential energy
• Mechanisms of ATP generation

  1. Substrate-level phosphorylation

  2. Oxidative phosphorylation

  3. Photophosphorylation
• Glucose movement into cells

  • Glucose absorption in GI tract and kidney via Na+-glucose symporters
  • Glucose entry into most other cells via facilitated diffusion using GluT transporters
  • Insulin increases insertion of GluT4 into plasma membranes, increasing glucose entry
• Glucose catabolism


  1. Glycolysis

  2. Formation of acetyl coenzyme A

  3. Krebs cycle

  4. Electron transport chain
• Glycolysis can occur under aerobic or anaerobic conditions, but the Krebs cycle and electron transport chain require oxygen (aerobic respiration)
• Glycolysis


  1. Glucose molecule is oxidized and two molecules of pyruvic acid are produced

  2. Reactions also produce two molecules of ATP and two energy-containing NADH + H+
• Formation of acetyl coenzyme A

  1. Transition step that prepares pyruvic acid for entrance into the Krebs cycle

  2. Also produces energy-containing NADH + H+ plus carbon dioxide (CO2)
• Krebs cycle reactions


  Oxidize acetyl coenzyme A and produce CO2, ATP, NADH + H+, and FADH2
• Electron transport chain reactions

  Oxidize NADH + H+ and FADH2 and transfer their electrons through a series of electron carriers
• Aerobic respiration


  Reactions of the Krebs cycle and electron transport chain that require oxygen
• Anaerobic conditions


  Oxygen is not available or at a low concentration
• Anaerobic glycolysis


  Glycolysis occurs by itself under anaerobic conditions
• Glycolysis


  Chemical reactions that split a 6-carbon molecule of glucose into two 3-carbon molecules of pyruvic acid
• Glycolysis does not require oxygen and can occur under aerobic or anaerobic conditions</b>
• If oxygen is not available, pyruvic acid is converted to lactic acid and the remaining steps of cellular respiration do not occur
• Glycolysis produces a net gain of two ATP, two NADH, and two H+
• Phosphofructokinase


  Enzyme that catalyzes a key regulatory step in glycolysis
• Phosphofructokinase activity is high


  Rate of glycolysis is high
• Phosphofructokinase activity is low

  Glucose is converted to glycogen for storage instead of entering glycolysis
• Conversion of pyruvic acid to acetyl coenzyme A

  1. Pyruvic acid enters the mitochondrial matrix

  2. Enzyme pyruvate dehydrogenase removes a molecule of carbon dioxide and oxidizes pyruvic acid to an acetyl group

  3. Acetyl group attaches to coenzyme A to form acetyl coenzyme A
• Decarboxylation is the loss of a molecule of CO2 by a substance
• Oxidation of one glucose molecule produces two molecules of pyruvic acid, two molecules of carbon dioxide, and two NADH + H+
• Krebs cycle


  Acetyl coenzyme A is oxidized and produces CO2, ATP, NADH + H+, and FADH2
• Each turn of the Krebs cycle produces three NADH, three H+, one FADH2, and one ATP
• Because each glucose molecule provides two acetyl CoA molecules, there are two turns of the Krebs cycle per glucose molecule
• Electron transport chain


  Series of electron carriers in the inner mitochondrial membrane that oxidize NADH + H+ and FADH2
• The electron transport chain transfers electrons to oxygen, which is the final electron acceptor, and produces water
• Krebs cycle


  The first molecule formed when an acetyl group joins the cycle
• Krebs cycle


  1. Reactions occur in the matrix of mitochondria

  2. Series of oxidation–reduction reactions

  3. Decarboxylation reactions that release CO2
• Krebs cycle


  • Oxidation–reduction reactions transfer chemical energy, in the form of electrons, to two coenzymes—NAD+ and FAD
  • Pyruvic acid derivatives are oxidized, and the coenzymes are reduced
  • One step generates ATP
• One turn of the Krebs cycle

  1. Starts with the production of citric acid

  2. Ends with the formation of oxaloacetic acid
• For each turn of the Krebs cycle, three NADH, three H+, and one FADH2 are produced by oxidation–reduction reactions, and one molecule of ATP is generated by substrate-level phosphorylation