topic 7

• aerobic respiration

  Aerobic respiration

  Aerobic respiration is made of four stages: glycolysis, the link reaction, the Krebs cycle and oxidative phosphorylation. During aerobic respiration, glucose is effectively burned inside our bodies (it reacts with oxygen) to produce carbon dioxide, water and lots of energy in the form of ATP. The overall equation for aerobic respiration is:
• Glycolysis

  The first stage of aerobic respiration
• Link reaction

  1. Takes place in the mitochondrial matrix

  2. Converts pyruvate into acetyl coenzyme A (acetyl CoA)

  3. Does not produce any energy in the form of ATP

  4. Produces reduced NAD and acetyl CoA
• Glycolysis


  1. Occurs in the cytoplasm

  2. Converts glucose (6-carbon molecule) into two 3-carbon molecules called pyruvate

  3. Does not require oxygen, so is an anaerobic process

  4. Involved in both aerobic and anaerobic respiration pathways
• Reduced NAD


  Will be used in oxidative phosphorylation
• Kreb's cycle


  Also known as the citric acid cycle, a series of reactions which generate reduced NAD and reduced FAD needed for oxidative phosphorylation
• Glycolysis


  1. Glucose is phosphorylated using phosphate groups from two ATP molecules

  2. ATP is hydrolysed into ADP and inorganic phosphate

  3. Forms an unstable molecule that breaks down into two 3-carbon triose phosphate (TP) molecules

  4. Hydrogen is removed from TP and transferred to NAD to form NADH

  5. Removal of hydrogen oxidises TP into pyruvate
• Acetyl CoA


  Will be used in the Krebs cycle
• Link reaction


  1. Removes a carbon atom from pyruvate, forming carbon dioxide

  2. Converts pyruvate into a two-carbon molecule called acetate

  3. Removes hydrogen from pyruvate, which is picked up by the coenzyme NAD to form reduced NAD

  4. Combines the acetate with coenzyme A (CoA) to form acetyl CoA
• Oxidative phosphorylation


  The last stage of aerobic respiration where most of the ATP is made
• Oxidative phosphorylation

  1. Uses the electrons carried by reduced NAD and reduced FAD

  2. Takes place across the inner mitochondrial membrane

  3. Involves the electron transport chain and chemiosmosis
• The conversion of triose phosphate to pyruvate produced four ATP molecules
• Kreb's cycle


  1. Acetyl CoA from the link reaction reacts with oxaloacetate

  2. Coenzyme A portion of acetyl CoA is removed and returns to the link reaction

  3. Citrate is produced

  4. Carbon and hydrogen are removed from citrate, forming carbon dioxide and reduced NAD

  5. Citrate is converted into a 5-carbon compound

  6. Decarboxylation and dehydrogenation occur, converting the 5-carbon compounds into oxaloacetate

  7. ATP, 2 molecules of reduced NAD, one molecule of FAD and carbon dioxide are also formed
• Reduced NAD and reduced FAD


  Release hydrogen atoms which split into hydrogen ions and electrons
• Electron transport chain


  1. Electrons are passed onto electron carriers embedded in the inner mitochondrial membrane

  2. Electrons travel along a series of electron carriers

  3. Electrons lose energy as they travel between carriers

  4. This energy is used to pump hydrogen ions from the mitochondrial matrix across the inner membrane
• Aerobic respiration


  Produces a total of 38 ATP molecules per one molecule of glucose respired
• Proton gradient

  Hydrogen ions accumulate in the intermembrane space, generating a proton gradient across the membrane
• Chemiosmosis


  1. Hydrogen ions flow back into the matrix through ATP synthase

  2. ATP synthase uses the movement of hydrogen ions (the proton motive force) to add a phosphate group onto ADP to form ATP
• Since two ATP molecules were used for the phosphorylation of glucose in the first step, this means there is a net gain of two ATP molecules in glycolysis
• The Kreb's cycle takes place twice for each glucose molecule that is respired aerobically
• Final electron acceptor

  Oxygen, which combines with electrons and hydrogen ions to form water
• One glucose molecule is converted into 2x pyruvate
• ATP production in aerobic respiration


  1. Glycolysis: direct production of 2 ATP

  2. Glycolysis: 2 reduced NAD are converted into 6 ATP (2 x 3) in oxidative phosphorylation

  3. Link reaction: 2 reduced NAD are converted into 6 ATP (2 x 3) in oxidative phosphorylation

  4. Krebs cycle: direct production of 2 ATP

  5. Krebs cycle: 6 reduced NAD are converted into 18 ATP (6 x 3) in oxidative phosphorylation

  6. Krebs cycle: 2 reduced FAD are converted into 4 ATP (2 x 2) in oxidative phosphorylation
• Metabolic poisons (e.g. cyanide)


  Disrupt oxidative phosphorylation by binding to electron carriers and inhibiting the movement of electrons along the electron transport chain
• Disruption of the electron transport chain


  Reduces chemiosmosis since a proton gradient is not established
• Disruption of the electron transport chain

  Inhibits the Krebs cycle since NAD and FAD are not regenerated
• Disruption of oxidative phosphorylation


  ATP production grinds to a halt, so processes requiring energy (e.g. heart muscle contraction) cannot take place, which can be deadly
• Oxidative phosphorylation


  The last stage of aerobic respiration where the reduced NAD (NADH) is used
• Respirometer


  Piece of apparatus used to measure the rate of respiration by measuring either the amount of oxygen used up by an organism or the amount of carbon dioxide produced
• Total ATP produced in aerobic respiration = 2 + 6 + 6 + 2 + 18 + 4 = 38 ATP
• The link reaction happens twice for every glucose molecule
• Link reaction

  The next stage of respiration after glycolysis, where the pyruvate moves into the mitochondria
• Anaerobic respiration


  Respiration that occurs in the absence of oxygen
• Anaerobic respiration in mammals

  Glucose can be converted into lactate (aka lactic acid) which releases a small amount of energy in the form of ATP
• Anaerobic respiration

  1. Glycolysis

  2. Pyruvate production with net release of 2 ATP

  3. Reduced NAD formation

  4. Lactate production from pyruvate with NAD regeneration
• The faster the amount of oxygen consumed

  The faster the rate of respiration
• Anaerobic respiration continuing

  Leads to build-up of lactate
• Each molecule of glucose produces two molecules of acetyl CoA, along with 2x carbon dioxide and 2x NADH
• Lactate breakdown

  1. Cells convert lactate back into pyruvate

  2. Pyruvate enters aerobic respiration at Krebs cycle
• Lactate conversion by liver cells


  1. Lactate converted into glucose

  2. Glucose can then be respired aerobically or stored for later use