Respiration

• Main stages in respiration and where they take place:

  • glycolysis - cytoplasm
  • link reaction - matrix of mitochondria
  • krebs cycle - matrix of mitochondria
  • oxidative phosphorylation via ETC - membranes of cristae
• Advantage of mitochondria having more cristae:

  • larger surface area for ATP synthase
  • to carry out oxidative phosphorylation
  • producing more ATP
• Outline the stages of glycolysis

  1. glucose is phosphporylated to glucose phosphate by 2x ATP
  2. glucose phosphate splits into 2x triose phosphate (TP)
  3. 2x TP is oxidised to 2x pyruvate

  Net gain of 2x reduced NAD and 2x ATP per glucose
• How does pyruvate from glycolysis enter the mitochondria?

  via active transport
• What happens during the link reaction?

  1. Oxidation of pyruvate to acetate
  2. CO2 is formed (decarboxylation)
  3. Acetate combines with coenzyme A to form acetylcoemzyme A
• Outline the stages of the krebs cycle

  1. 2C acetyl coA combines with 4C compound
  2. 6C compound loses CO2 (decarboxylation)
  3. 5C compound loses CO2 (decarboxylation)
  4. One molecule of ATP is produced by substrate-level phosphorylation
  5. FAD and NAD accept hydrogen and become reduced
  6. 4C compound is regenerated and the cycle begins again
• What is the significance of the krebs cycle?

  • breaks down macromolecules into smaller ones
  • regenerates the 4C compound, which would otherwise accumulate
  • source of intermediate compounds used in the manufacture of other substances
  • Respiratory substrates from the breakdown of lipids and amino acids enter the krebs cycle
• What is the electron transfer chain (ETC)?

  Series of carrier proteins embedded in membrane of the cristae of mitochondria.

  Produces ATP through oxidative phosphorylation via chemiosmosis during aerobic respiration.
• Oxidative phosphorylation process:

  1. electrons released from reduced NAD & FAD undergo successive redox reactions
  2. the energy released is coupled to maintaining proton gradient or released as heat
  3. oxygen acts as final electron acceptor
• Role of oxygen for production of ATP

  • ATP formed as electrons pass along transport chain
  • oxygen is terminal electron acceptor so electrons cannot be passed along electron transport chain if no O2 to accept them
  • forms H2O by accepts H+ from reduced NAD and FAD
• How is a proton concentration gradient established during chemiosmosis in aerobic respiration?

  Some energy released from the ETC is couples to the active transport of protons from the mitochondrial matrix into the intermembrane space
• How does chemiosmosis produce ATP during aerobic respiration?

  protons move down their concentration gradient from the intermembrane space into the mitochondrial matrix via the channel protein ATP synthase.
• State the role of oxygen in aerobic respiration

  Final electron acceptor in electron transfer chain
• What is the benefit of an electron transfer chain rather than a single reaction?

  • energy is released gradually
  • less energy is released as heat
• Name 2 types of molecule that can be used as alternative respiratory substrates

  • proteins
  • lipids
• How can lipids act as an alternative respiratory substrate?

  1. lipids are hydrolysed to glycerol and fatty acids
  2. glycerol is phosphorylated and converted int triose phosphate
  3. it enters glycolysis
  4. fatty acids are broken down into acetate
  5. acetate enters the link reaction
• How can amino acids act as an alternative respiratory substrate

  1. proteins are hydrolysed to amino acids
  2. these are deaminated and enter the respiratory pathway at different points depending on the number of carbon atoms
• What happens to the lactate produced in anaerobic respiration?

  Transported to liver via bloodstream, where it is oxidised to pyruvate
• What happens during anaerobic respiration in some microorganisms?

  • only glycolysis continues
  • pyruvate is decarboxylated to form ethanal
  • Ethanal is reduced to ethanol using reduced NAD to produce oxidised NAD for further glycolysis
• What is the advantage of producing ethanol/lactate during anaerobic respiration?

  converts reduced NAD back into NAD so glycolysis can continue
• Compare aerobic and anaerobic respiration

  • both involve glycolysis
  • both require NAD
  • both produce ATP
• Contrast aerobic and anaerobic respiration

  AEROBIC

  • produces more ATP
  • does not produce ethanol or lactate

  ANAEROBIC

  • produced fewer ATP
  • produced ethanol or lactate
• Why does an increase in temperature lead to a decrease in rate of respiration?

  1. respiration is catalysed by enzymes which are proteins
  2. hydrogen bonds in the tertiary structure break
  3. active site changes shape and is denatured
  4. substrate can no longer bind the active site
  5. so fewer enzyme-substrate complexes form
• What happens in the krebs cycle?

  Series of redox reactions produces:

  • ATP by substrate-level phosphorylation
  • Reduced coenzymes
  • CO2 from decarboxylation
• Glycolysis flow chart


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• What happens in the electron transfer chain (ETC)?

  • Electrons released from reduced NAD & FAD undergo successive redox reactions
  • The energy released is coupled to maintaining proton gradient or released as heat
  • Oxygen acts as final electron acceptor
• Name the stages in respiration that produce ATP by substrate-level phosphorylation

  • Glycolysis (anaerobic)
  • Krebs cycle (aerobic)
• Disadvantage of producing lactate during anaerobic respiration?

  Acidic, so decreases pH.

  Results in muscle fatigue.