Cellular Respiration

1. Cellular Respiration Topic 3.7 and 3.8

2. Assessment Statements: Core 3.7.1 Define cell respiration. 3.7.2 State that, in cell respiration, glucose in the cytoplasm is broken down by glycolysisinto pyruvate, with a small yield of ATP. 3.7.3 Explain that, during anaerobic cell respiration, pyruvate can be converted in the cytoplasm into lactate, or ethanol and carbon dioxide, with no further yield of ATP. 3.7.4 Explain that, during aerobiccell respiration, pyruvate can be broken down in the mitochondrion into carbon dioxide and water with a large yield of ATP.

3. Assessment Statements: Higher Level

4. Energy metabolism and REDOX reactions • Metabolism is the sum of all of the chemical reactions in an organism: catabolic (breakdown) and anabolic (synthetic) • Respiration is a catabolic pathway • Photosynthesis is an anabolic pathway • The two processes are closely linked in plants • REDOX (oxidation-reduction) reactions play a key role in energy flow through organisms • This is because the electrons flowing from one molecule to another are carrying energy with them

5. REDOX reactions OIL RIG LEO says GER

6. Definition of cellular respiration Controlled release of energy from organic compounds to produce ATP • Cells break down organic compounds by SLOW oxidation • Chemical energy is stored in covalent bonds • By releasing energy in a controlled way, it can be trapped in the ‘useful’ form of ATP

7. REDOX reactions in respiration Cells tap energy from electrons transferred from organic fuels to oxygen Glucose gives up energy as it is oxidized: it transfers its electrons (and energy) to water The protons follow the electrons to produce water Loss of hydrogen atoms Energy Gain of hydrogen atoms

8. Where Does Cellular Respiration Take Place? glycolysis occurs in the cytoplasm Krebs Cycle & ETC Takeplace in the mitochondria

10. Cellular Respiration: Standard level How does the process of cellular respiration yield ATP (chemical energy) from food? • What do you already know about cellular respiration? • What organelle in the cell is the “powerhouse” that makes energy for the cell?

11. What is ATP? • Energy ‘currency’ used by all cells • Adenosine triphosphate • Organic molecule containing high-energy phosphate bonds

12. Chemical Structure of ATP Adenine Base 3 Phosphates Ribose Sugar

13. How Do We Get Energy From ATP? By breaking the high- energy bonds between the last two phosphates in ATP ATP hydrolase (ATP’ase) catalyses the breakdown of ATP into ADP + Pi

14. Each day, you hydrolyse 1025 ATP molecules ATP-ase ATP Synthetase

15. HYDROLYSIS (Adding H2O) H2O

16. How is ATP re-made? • Substrate-level phosphorylation (using enzymes: in the cytoplasm of the cell and the matrix of the mitochondrion) • Chemiosmosis (in the mitochondria, using ATP synthase)

17. Substrate level phosphorylation and chemiosmosis GLYCOLYSIS ELECTRONTRANSPORT CHAINAND CHEMIOSMOSIS KREBSCYCLE Glucose Pyruvicacid Substrate Level Phos. Substrate Level Phos. Oxidative Phos.

18. REDOX reactions in respiration Cells tap energy from electrons transferred from organic fuels to oxygen Glucose gives up energy as it is oxidized: it transfers its electrons (and energy) to water The protons follow the electrons to produce water Loss of hydrogen atoms Energy Gain of hydrogen atoms

19. Hydrogen carriers such as NAD+ shuttle electrons in redox reactions Enzymes remove electrons from glucose molecules and transfer them to a coenzyme OXIDATION Dehydrogenaseand NAD+ REDUCTION

20. Redox reactions release energy when electrons “fall” from a hydrogen carrier to oxygen • NADH delivers electrons to a series of electron carriers in an electron transport chain • As electrons move from carrier to carrier, their energy is released in small quantities Energy released and nowavailable for making ATP ELECTRON CARRIERSof the electron transport chain Electron flow

21. Two mechanisms generate ATP • ATP can be made by transferring phosphate groups from organic molecules to ADP • This process is called substrate-level phosphorylation • Occurs in cytoplasm and in matrix of the mitochondrion

22. Two mechanisms generate ATP High H+concentration 1. Cells use the energy released by “falling” electrons to pump H+ ions across a membrane • The energy of the gradient is harnessed to make ATP by the process of chemiosmosis • also known as oxidative phosphorylation ATP synthase uses gradient energy to make ATP Membrane Electron transport chain ATPsynthase Energy from Low H+concentration Figure 6.7A

23. Definition of cellular respiration Controlled release of energy from organic compounds to produce ATP • Cells break down organic compounds by SLOW oxidation • Chemical energy is stored in covalent bonds • By releasing energy in a controlled way, it can be trapped in the ‘useful’ form of ATP

26. Cellular Respiration Breakdown of one glucose results in 36 to 38 ATP molecules • Metabolic Pathway that breaks down carbohydrates • Process is exergonic as high-energy glucose is broken into CO2 and H2O • Process is also catabolic because glucose breaks into smaller molecules

27. Equations for aerobic respiration All of these are fine!....

28. Equation for Cellular Respiration C6H12O6 + 6O2 YIELDS 6CO2 + 6H20 + e- + 36-38ATP + heat

29. Stages of Cellular Respiration • Glycolysis ALWAYS OCCURS • Anaerobic pathways if no oxygen available (Lactic acid and Ethanolfermentation) • Aerobic pathways if oxygen available (Link reaction, Krebs cycle, electron transport chain)

31. Where Does Cellular Respiration Take Place? glycolysis occurs in the cytoplasm Krebs Cycle & ETC Takeplace in the mitochondria

33. Glycolysis: Always the initial stage of respiration • Location: cytoplasm • Substrate: glucose • Requires input of 2 ATP • Products: pyruvate, (NADH), 4 ATP Glycolysis is an anaerobic process: no oxygen required the movie...

34. Glycolysis

35. Summary of glycolysis • Occurs in the cytoplasm of the cell • Two ATP molecules are used to start the process (‘energy investment phase’) • A total of 4 ATP’s are produced (net gain of 2 ATP) • 2 molecules of NADH are produced • Involves substrate level phosphorylation, lysis, oxidation and ATP formation • Controlled by enzymes: when ATP levels in the cell are high, feedback inhibition will block the first enzyme in the pathway • Produces 2 pyruvate molecules at the end

36. If no oxygen is available, glycolysis (anaerobic) is followed by fermentation (anaerobic)

37. Why fermentation? In the absence of oxygen, glycolysis soon stops unless there is an alternative acceptor for the electrons produced from the glycolytic pathway

38. Fermentation 1. Alcoholic fermentation Pyruvate is converted into ethanol plus carbon dioxide and NAD+ • Lactate fermentation Pyruvate is converted into lactate and NAD+

39. Alcoholic fermentation in yeast

40. Alcoholic fermentation in yeast • Pyruvate is produced from glycolysis • 3-carbon pyruvate is converted to 2-carbon ethanol and carbon dioxide • Generation of carbon dioxide helps bread products to rise • Yeast is used to produce ethanol

41. Lactate fermentation in mammals • Lactate is a 3-carbon molecule • NAD+ is regenerated to allow glycolysis to continue

42. Aerobic respiration: Higher level 8.1.4: Explain aerobic respiration: the Link reaction, the Krebs cycle, the role of NADH and H+, the electron transport chain and the role of oxygen 8.1.5: Explain oxidative phosphorylation in terms of chemiosmosis

43. Aerobic respiration • Takes place in the mitochondria of eukaryotic cells • Substrate: pyruvate • Produces LOTS of ATP (28 – 38 ATP): 90% of total ATP from respiration • Also produces carbon dioxide, water and heat • Oxygen is the final electron acceptor

44. Aerobic respiration • 2 pyruvate molecules enter the mitochondrion • Pyruvate loses a CO2 molecule and becomes acetyl CoA • Krebs cycle produces 2 ATP, 4 CO2, 6 NADH and 3 FADH2 • Electron transport chain produces 34 ATP and water • Aerobic respiration completelyoxidises glucose • Anaerobic respiration does not completely oxidise glucose – ethanol, lactate and carbon dioxide are by-products

45. Get to know your mitochondrial structure!

47. Stages of aerobic respiration • The ‘link’ reaction • The Krebs cycle • The electron transport chain • Chemiosmosis and oxidative phosphorylation

48. The Link Reaction Steps 2 in aerobic respiration (step 1 is glycolysis in the cytoplasm) After glycolysis, when there is ample oxygen… 2 pyruvate molecules from glycolysis move into the matrix of the mitochondrion for the Link reaction and the Krebs cycle

49. Matrix – Link Reaction 2 Krebs Cycle 2

50. The Link reaction The link reaction converts pyruvate (3C) into acetyl Coenzyme A (2C), producing carbon dioxide and NADH in the process