chapter 6

• Cellular respiration

  The process that makes ATP
• Aerobic cellular respiration is used by all plants and animals, as well as many microbes
• ATP

  The form of energy cells are able to use
• Aerobic cellular respiration

  A series of chemical reactions where the reactants are glucose and oxygen, and the products are carbon dioxide, water, and ATP
• Stage 1: Glycolysis


  1 molecule of glucose is split into 2 three-carbon molecules of pyruvate, releasing 2 molecules of ATP
• Transition step

  2 molecules of pyruvate are converted into 2 molecules of Acetyl CoA
• Stage 2: Krebs cycle

  Acetyl CoA molecules are disassembled inside mitochondria during the Krebs cycle, transferring energy to electrons
• Stage 3: Electron transport chain

  Electrons are unloaded into the electron transport chain to produce more ATP using potential energy in the electrons, requiring oxygen and releasing water
• Glycolysis reactions occur in the cytosol of cells, and the rest of the reactions depend on the cell type
• For prokaryotic cells, Krebs Cycle occurs in the cytosol and the electron transport chain in the cell membrane
• Glycolysis

  1. Occurs outside of the mitochondrion, in the cytoplasm

  2. Requires an input of two ATP to "activate" glucose

  3. Glucose is converted into two 3-carbon intermediates called PGAL

  4. Each PGAL molecule proceeds to the energy extraction reactions of glycolysis

  5. First, each PGAL is oxidized, producing two NADH molecules

  6. PGAL donates its phosphate groups to ADP molecules, producing ATP molecules via substrate-level phosphorylation

  7. In total, four ATP are produced in glycolysis, with a net yield of two ATP

  8. These reactions do not require oxygen, making glycolysis anaerobic

  9. Glycolysis requires: 1 glucose, 2 NAD+, 2 ADP; Glycolysis yields: 2 pyruvate, 2 electron-carrying NADH molecules, 2 ATP
• In substrate-level phosphorylation, an enzyme transfers a phosphate from a molecule to ADP
• Transition step

  1. The two pyruvate molecules produced in glycolysis undergo an oxidation reaction as they enter the mitochondrion, sometimes called the transition step

  2. A carbon atom is stripped from each pyruvate, leaving the cell as a carbon dioxide molecule, while NAD+ is reduced to NADH
• Krebs cycle

  The two acetyl CoA molecules are oxidized, yielding 4 ATP, 2 FADH2, 6 NADH
• At the end of the transport chain, electrons are donated to an oxygen atom, which combines with hydrogens to form water. Oxygen is the final electron acceptor. Without it, the chain shuts down
• In the absence of oxygen, a cell can re-create in other pathways, called anaerobic respiration and fermentation
• Different electron acceptors allow for less ATP production than oxygen
• The pyruvate is converted into alcohol, lactic acid, or other byproducts
• Photosynthesis and respiration are connected in many ways: water, oxygen, carbon dioxide, sugars
• Photosynthesis may have evolved from glycolysis, since some Calvin cycle reactions are the reverse of glycolysis reactions