Respiration Respiration is a catabolic pathway that is controlled by different enzymes It releases energy from a molecule of 6 carbon glucose by breaking it down into smaller simpler molecules Respiration ID: 1038423
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1. Higher BiologyUnit 22.2 Cellular Respiration
2. RespirationRespiration is a catabolic pathway that is controlled by different enzymes.It releases energy from a molecule of 6 carbon glucose by breaking it down into smaller, simpler molecules.
3. RespirationRespiration consists of 3 metabolic pathways;GlycolysisCitric acid cycleElectron transport chain Each pathway has a different location in the cell.
4. Location of PathwaysMetabolism and survivalGlycolysis occurs in the cytoplasm.Citric acid cycle occurs in the central matrix of mitochondria.Electron transport chain occurs in cristae of mitochondria.
5. Structure of Mitochondrion site of citric acid cyclesite of electron transport chain
6. Glycolysisoccurs in the cytoplasmis anaerobic – it does not require oxygensplits one molecule of glucose (6C) into two molecules of pyruvate (3C)
7. GlycolysisDuring glycolysis there is a net gain of 2ATP. This is because;The first part of glycolysis uses 2 ATP. This is the energy investment phase.The second part produces 4 ATP. This is the energy pay off phase.
8. GlycolysisHydrogen ions are removed.They are removed by a dehydrogenase enzyme.The H ions then combine with a hydrogen acceptor called NAD.This reduces NAD to NADH.
9. Glycolysis Glucose6C2ATP 2ADP + 2Pi4ADP + 4Pi4ATPPyruvate 3C2NAD2NADH2 (reduced)To electron transport chain if oxygen is presentNet gain of 2ATP moleculesFermentation if oxygen is absentEnergy investment phaseEnergy pay off phase
10. Aerobic RespirationIf oxygen is present aerobic respiration takes place and;2NADH carry H ions onto the electron transport chain.Pyruvate progresses to the citric acid cycle.
11. Aerobic RespirationPyruvate is broken down to carbon dioxide and an acetyl group.The acetyl group combines with coenzyme A to form a 2C compound called acetyl coenzyme A (acetyl coA).Dehydrogenase removes more H ions which reduce NAD to form NADH. pyruvateacetyl Co ANADNADHCO2To citric acid cycle
12. Citric Acid CycleOccurs in the matrix of mitochondria.2C acetyl coA enters the cycle and combines with a 4C compound called oxaloacetate.This forms a 6C compound called citrate.A series of enzyme-controlled reactions then regenerate oxaloacetate from citrate.
13. Citric Acid CycleDehydrogenase removes H ions along with high energy electrons.They combine with NAD to form NADH and another coenzyme called FAD to form FADH2.These transport H ions and high energy electrons to the electron transport chain.ATP and carbon dioxide are also produced.
14. QuestionsExplain why the phosphorylation of intermediates in glycolysis is described as an energy investment phase. (2)State the role of dehydrogenase enzymes in glycolysis and the citric acid cycle. (1)Describe the role of the co-enzymes NAD and FAD. (2)
15. ATP ProductionIn respiration so far;ATP has been synthesised directlyHydrogen ion and electron carriers NADH and FADH2 have been synthesised NADH and FADH2 are now going to be used to produce more ATP molecules, using the enzyme ATP synthase.
16. ATP SynthaseTo synthesise most of its ATP, a cell uses a source of high energy electrons.These are used to pump H ions across a membrane.The return flow of the H ions rotates part of the membrane protein ATP synthase which catalyses the synthesis of ATP.
17. ATP SynthaseATP synthase is found in membranes of mitochondria and chloroplasts.Hydrogen ions flow from a high concentration to a low concentration across ATP synthase.This makes part of ATP synthase rotate and catalyse the synthesis of ATP from ADP and Pi
18. Electron Transport ChainThe electron transport chain is a series of proteins imbedded in the cristae of mitochondria. H ions and the high energy electrons are brought here by NAD and FAD from glycolysis and the citric acid cycle.These will be used to produce many molecules of ATP using ATP synthase.
19. Electron Transport ChainAt the cristae, NADH and FADH2 pass high-energy electrons along the electron transport chain. The energy from these electrons cause H ions to be pumped across the membrane.ATP synthase
20. Electron Transport ChainThe hydrogen ions pass through ATP synthaseThis causes ATP synthase to produce ATP (from ADP and Pi).
21. Electron Transport ChainWhen the electrons come to the end of the electron transport chain they combine with oxygen.At the same time, the oxygen joins to a pair of hydrogen ions to form water.Oxygen is the final hydrogen acceptor. Without it, the electron transport chain cannot not proceed and ATP is not made here.
22. Electron Transport Chain
23. QuestionsName the enzyme embedded in the inner membrane of a mitochondrion, responsible for the regeneration of ATP. (1)Describe the role of the high-energy electrons transported to the electron transport chain. (2)State the role of oxygen in the electron transport chain. (1)
24. FermentationIf oxygen is not available, then the citric acid cycle and electron transport chain cannot proceed.This is because there is no final hydrogen acceptor and hydrogen cannot pass through the electron transport chain.After glycolysis, pyruvate is fermented.This produces different products in different cell types.
25. Fermentation - AnimalsThe body builds up an oxygen debt.Pyruvate (3C) is converted into lactate (3C)If lactate builds up in tissues, it causes muscle fatigue.When oxygen becomes available the lactate can be converted back into pyruvate.
26. Fermentation – Plants & YeastsPyruvate (3C) is converted into ethanol (2C) and carbon dioxide (1C)Even if oxygen becomes available to the cell, the ethanol cannot be converted back into pyruvate (as a carbon atom is lost when carbon dioxide is released).
27. Respiration Vs Fermentation RespirationFermentationOxygen requirementsOxygen requiredNo oxygen requiredBreakdown of glucoseComplete breakdown(efficient)Incomplete breakdown (inefficient)End productsCarbon dioxide & waterAnimals & some bacteria: lactatePlants & yeasts; ethanol & CO2 Energy yield38 ATP per molecule of glucose2 ATP per molecule of glucoseLocationCytoplasmMatrix of mitochondriaCristae of mitochondriaCytoplasm
28. Alternative SubstratesOther carbohydrates;Starch and glycogen are complex carbohydrates made of glucose molecules.Other sugar molecules such as maltose and sucrose can be converted to the intermediates of glycolysis.
29. Alternative SubstratesFat is broken down to fattyacids and glycerol.Glycerol can then be converted to an intermediate of glycolysis.Fatty acids are broken down to intermediates of the citric acid cycle.
30. Alternative SubstratesProteins are brokendown to amino acids. Any amino acids not usedduring protein synthesisare converted tointermediates ofglycolysis or the citricacid cycle.
31. Key PointsGlycolysisOccurs in the cytoplasmBreaks down glucose to pyruvate.Phosphorylation of intermediates uses 2ATP in an energy investment phase.4ATP is produced an energy pay-off stage.This gives a net gain of 2ATP.H ions are removed by dehydrogenase enzymes.H ions join to NAD to reduce it to NADH.H ions are transported to the electron transport chain.
32. Key PointsPyruvate progresses to the citric acid cycle if oxygen is available.Pyruvate is broken down to an acetyl group.The acetyl group combines with coenzyme A to form acetyl CoA.Acetyl CoA is transferred to the citric acid cycle.
33. Key PointsCitric Acid CycleOccurs in the matrix of mitochondriaAcetyl CoA (2C) joins to oxaloacetate (4C).This forms citrate (6C).Citrate proceeds through the citric acid cycle to regenerate oxaloacetate.ATP and carbon dioxide are produced during this.H ions and high-energy electrons are removed by dehydrogenases.These reduce NAD and FAD to NADH and FADH2.They are taken to the electron transport chain.
34. Key PointsElectron Transport ChainA collection of proteins attached to the cristae of mitochondria.High-energy electrons release energy.This is used to pump H ions across the inner mitochondrial membrane.The return flow of H ions rotates ATP synthase.This generates ATP.The final hydrogen acceptor is oxygen.Oxygen combines with H ions to form water.
35. Key PointsFermentation
36. Key PointsGlucose is the main substrate for respiration. However, alternative substrates include;StarchGlycogenOther sugars such as maltose or sucroseFatty acidsGlycerolAmino acids