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Respiration

JIS. Carbon dioxide. Glucose + Oxygen. +. +. Water. Energy. 6CO 2 + 6H 2 O + 38ATP. C 6 H 12 O 6 + 6O 2. Respiration. 1. Glycolysis 2. Link reaction 3. Krebs cycle 4. Electron transfer chain. JIS. Structure of mitochondria.

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Respiration

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  1. JIS Carbon dioxide Glucose + Oxygen + + Water Energy 6CO2 + 6H2O + 38ATP C6H12O6 + 6O2 Respiration 1. Glycolysis2. Link reaction3. Krebs cycle4. Electron transfer chain

  2. JIS Structure of mitochondria Glycolysis - in the cytoplasm of the cell, i.e., NOT in the mitochondria Link reaction - in the fluid-filled matrix of the mitochondria Krebs cycle - also takes place in the fluid-filled matrix of the mitochondria Electron transfer chain - takes place on the membrane surfaces of the cristae (the folds on the inner membrane of the mitochondria)

  3. JIS ATP ATP ADP + Pi ADP + Pi 2ADP + 2Pi 2ADP + 2Pi 2ATP NAD NAD 2ATP reducedNAD reducedNAD Glycolysis I (Glyco = glucose; lysis = split) Glucose Glyceraldehyde 3 – phosphate (GALP) Glyceraldehyde 3 – phosphate (GALP) Pyruvate Pyruvate

  4. JIS GLUCOSE 2 PYRUVATE 4 ATP 2 ATP 2 NAD 2 reduced NAD Glycolysis II The reactants and products of glycolysis can be summarised as: GLYCOLYSIS } These reactions take place in the cytoplasm of the cell To the Link Reaction

  5. JIS NAD Reduced NAD (NADH) CO2 CH3COCOO- + NAD+ + H20 CH3COO- + NADH + H+ + CO2 Link reaction I (links Glycolysis with the Krebs cycle) Pyruvate (3C) 1 2 Acetate (2C) In reaction 1, the pyruvate is oxidised by the NAD (which is reduced). In reaction 2, a CO2 molecule is removed from the pyruvate. The reactions here are therefore described as oxidative decarboxylation.

  6. JIS Acetate Acetyl Coenzyme A 2 CO2 2 ATP GLUCOSE 2 Acetyl CoA } To the Krebs cycle 4 reduced NAD Link reaction II (Acetyl Coenzyme A) The Acetate is not left in solution. It is picked up by a carrier molecule – Coenzyme A – forming “Acetyl Coenzyme A”, sometime abbreviated to Acetyl CoA. These reactions take place in the matrix of the mitochondria Summary – the story so far. . .

  7. JIS NAD reduced NAD CoA Acetyl CoA(2C) CO2 reduced NAD ADP + Pi CO2 ATP NAD NAD reduced NAD reduced FAD FAD Note that, because the breakdown of glucose results in 2 molecules of Acetyl CoA being formed, the Krebs cycle goes “round” twice for each molecule of glucose. Krebs cycle I 6C compound(citrate) 5C compound(α-ketoglutarate) 4C compound(oxaloacetate) 4C compounds(fumarate, then malate) 4C compound(succinate)

  8. JIS Krebs cycle II Summary In each cycle, the following events occur: 2 molecules of CO2 are produced, and released 1 molecule of ATP is produced 3 molecules of NAD are reduced 1 molecule of FAD is reduced The initial 4-carbon molecule (oxaloacetate) has been regenerated Again, remember that for each glucose molecule being respired, the Krebs cycle is operated twice. Current tallies of main reactants (from 1 molecule of glucose):

  9. JIS ATP ATP ATP Electron transfer chain I All the way through the pathways so far, NAD and FAD have picked up pairs of electrons from the glucose (and its remains). In other words, they have been reduced, as the glucose has been gradually oxidised. Now, in the final stages of respiration, the reduced NAD and FAD molecules are oxidised themselves, back to NAD and FAD. These exothermic reactions provide the energy for creating large quantities of ATP. The diagram below shows the path of a pair of electrons (in a solid line) as they are passed from carrier to carrier. H2O Reduced electron carrier 2 reduced NAD e- carrier 1 e- carrier 3 2e- + 2H+ e- carrier 2 NAD Reduced electron carrier 1 Reduced electron carrier 3 ½O2

  10. JIS H2O Reduced electron carrier 2 reduced NAD e- carrier 1 e- carrier 3 2e- + 2H+ e- carrier 2 NAD Reduced electron carrier 1 Reduced electron carrier 3 ½O2 ATP ATP ATP Electron transfer chain II • Points to note: • 3 molecules of ATP are synthesised for each molecule of NAD oxidised. • As there are 10 molecules of reduced NAD per glucose molecule, this makes 30ATP • The 2 molecules of reduced FAD synthesised during the Krebs cycle skip Electron carrier 1, and enter the chain at Electron carrier 2. This results in 2 ATP per FAD, and 4 ATP in total. • Total ATP count from the Electron transfer chain = 34 ATP

  11. JIS 6O2 6H20 34 ATP Respiration - summary GLUCOSE GLYCOLYSIS 2 reduced NAD 2 pyruvate LINKREACTION 2 reduced NAD 2 ATP 2 acetyl CoA KREBS CYCLE 6 reduced NAD +2 reduced FAD 2 CO2 ELECTRONTRANSFERCHAIN 4 CO2 + 2 ATP

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