1. Higher Biology Unit 2 2.2 Cellular Respiration

2. 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.

3. Respiration Respiration consists of 3 metabolic pathways; 1.Glycolysis 2.Citric acid cycle 3.Electron transport chain Each pathway has a different location in the cell.

4. Location of Pathways Metabolism and survival Glycolysis 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 cycle site of electron transport chain

6. Glycolysis occurs in the cytoplasm is anaerobic – it does not require oxygen splits one molecule of glucose (6C) into two molecules of pyruvate (3C)

7. Glycolysis During 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. Glycolysis Hydrogen 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 Glucose 6C 2ATP 2ADP + 2P i 4ADP + 4P i 4ATP Pyruvate 3C 2NAD 2NADH 2 (reduced) To electron transport chain if oxygen is present Net gain of 2ATP molecules Fermentation if oxygen is absent Energy investment phase Energy pay off phase

10. Aerobic Respiration If 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 Respiration Pyruvate 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. pyruvate acetyl Co A NAD NADH CO 2 To citric acid cycle

12. Citric Acid Cycle Occurs 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 Cycle Dehydrogenase removes H ions along with high energy electrons. They combine with NAD to form NADH and another coenzyme called FAD to form FADH 2. These transport H ions and high energy electrons to the electron transport chain. ATP and carbon dioxide are also produced.

14. Questions 1.Explain why the phosphorylation of intermediates in glycolysis is described as an energy investment phase.(2) 2.State the role of dehydrogenase enzymes in glycolysis and the citric acid cycle.(1) 3.Describe the role of the co-enzymes NAD and FAD. (2)

15. ATP Production In respiration so far; ATP has been synthesised directly Hydrogen ion and electron carriers NADH and FADH 2 have been synthesised NADH and FADH 2 are now going to be used to produce more ATP molecules, using the enzyme ATP synthase.

16. ATP Synthase To 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 Synthase ATP 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 P i

18. Electron Transport Chain The 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 Chain At the cristae, NADH and FADH 2 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 Chain The hydrogen ions pass through ATP synthase This causes ATP synthase to produce ATP (from ADP and Pi).

21. Electron Transport Chain When 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. Questions 1.Name the enzyme embedded in the inner membrane of a mitochondrion, responsible for the regeneration of ATP.(1) 2.Describe the role of the high-energy electrons transported to the electron transport chain.(2) 3.State the role of oxygen in the electron transport chain.(1)

24. Fermentation If 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 - Animals The 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 & Yeasts Pyruvate (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 RespirationFermentation Oxygen requirements Oxygen requiredNo oxygen required Breakdown of glucose Complete breakdown (efficient) Incomplete breakdown (inefficient) End products Carbon dioxide & water Animals & some bacteria: lactate Plants & yeasts; ethanol & CO 2 Energy yield 38 ATP per molecule of glucose 2 ATP per molecule of glucose Location Cytoplasm Matrix of mitochondria Cristae of mitochondria Cytoplasm

28. Alternative Substrates Other 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 Substrates Fat is broken down to fatty acids 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 Substrates Proteins are broken down to amino acids. Any amino acids not used during protein synthesis are converted to intermediates of glycolysis or the citric acid cycle.

31. Key Points Glycolysis Occurs in the cytoplasm Breaks 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 Points Pyruvate 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 Points Citric Acid Cycle Occurs in the matrix of mitochondria Acetyl 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 FADH 2. They are taken to the electron transport chain.

34. Key Points Electron Transport Chain A 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 Points Fermentation

36. Key Points Glucose is the main substrate for respiration. However, alternative substrates include; Starch Glycogen Other sugars such as maltose or sucrose Fatty acids Glycerol Amino acids