Respiration

• What is aerobic respiration?

  Aerobic respiration is a catabolic, enzyme-controlled reaction that occurs inside cells to provide energy.
• Why do all living organisms carry out respiration?

  All living organisms carry out respiration to provide energy necessary for their metabolic processes.
• What types of substrates are broken down during aerobic respiration?

  Energy-rich respiratory substrates such as glucose or fatty acids are broken down to release energy.
• What happens to high-energy bonds during aerobic respiration?

  High-energy bonds (C-C, C-H, and C-OH) are broken and lower-energy bonds are formed.
• What is the fate of the excess energy released during aerobic respiration?

  The excess energy released is used to phosphorylate ADP to form ATP or is released as heat energy.
• What are the main steps of glycolysis and where does it occur?

  • Occurs in the cytoplasm

  1. Glucose is phosphorylated using 2 ATP into hexose phosphate.
  2. Hexose phosphate splits into two triose phosphate molecules.
  3. Oxidation of triose phosphate yields 2 ATP each by substrate level phosphorylation (net gain of 2 ATP).
  4. Dehydrogenation releases 2 Hydrogen picked up by NAD.
  5. 2 pyruvate diffuse into the mitochondria.
• What is the net gain of ATP from glycolysis?

  The net gain of ATP from glycolysis is 2 ATP.
• What occurs during the link reaction in the mitochondrial matrix?

  1. Oxidative decarboxylation of pyruvate releases carbon dioxide.
  2. Dehydrogenation releases pairs of hydrogen atoms converting NAD to reduced NAD.
  3. Coenzyme A forms acetyl CoA (2C) which enters the Krebs cycle.
• What are the main steps of the Krebs cycle and where does it occur?

  • Occurs in the mitochondrial matrix

  1. Acetate from acetyl CoA combines with a 4C compound to form a 6C compound.
  2. Decarboxylation forms a 5C compound and reduces NAD.
  3. Decarboxylation forms a 4C compound, reduces NAD, and produces 1 ATP.
  4. Dehydrogenation forms reduced FAD.
  5. Dehydrogenation forms reduced NAD.
• What is the role of reduced NAD and reduced FAD in the electron transport chain?

  Reduced NAD and reduced FAD deliver pairs of hydrogen atoms to the electron transport chain.
• What happens to oxygen in the electron transport chain?

  Oxygen is the final acceptor in the electron transfer chain and is reduced to water.
• How do lipids and proteins serve as respiratory substrates?

  • Lipids:
  • Glycerol is converted into triose phosphate for glycolysis.
  • Fatty acids are split into 2C acetate fragments for the Krebs cycle as acetyl CoA.
  • Proteins:
  • Amino acids are deaminated into ammonia and keto acids.
  • Some keto acids (like pyruvate) enter the link reaction, others enter the Krebs cycle.
• How many times do the link reaction and Krebs cycle occur for each molecule of glucose?

  The link reaction and Krebs cycle happen twice for each molecule of glucose.
• What is the total ATP yield from one molecule of glucose during aerobic respiration?

  • From substrate level phosphorylation:
  • 2 ATP from glycolysis
  • 2 ATP from Krebs cycle
  • From reduced NAD:
  • 2 reduced NAD from glycolysis (releasing 6 ATP)
  • 2 reduced NAD from link reaction (releasing 6 ATP)
  • 6 reduced NAD from Krebs cycle (releasing 18 ATP)
  • From reduced FAD:
  • 2 reduced FAD from Krebs cycle (releasing 4 ATP)
• What is the total ATP yield from reduced NAD and reduced FAD during aerobic respiration?

  The total ATP yield from reduced NAD is 30 ATP and from reduced FAD is 4 ATP.