How Cells Release Chemical Energy

1. How Cells Release Chemical Energy Chapter 7 Slide with a red dot may be tested upon, those without are for information purposes only

2. Objectives Today • Know the meaning of the term "metabolism." • Understand how cellular energy is produced from a glucose molecule during cellular respiration. • Discuss how the availability of oxygen determines the pathway by which ATP is produced.

3. Metabolism • is the complete set of chemical reactions that occur in living cells. • These processes are the basis of life, allowing cells to grow and reproduce, maintain their structures, and respond to their environments.

4. Producing the Universal Currency of Life All energy-releasing pathways • require characteristic starting materials - substrates • yield predictable products and by-products • produce ATP • ATP is the universal currency molecule of all life

5. ATP Is Universal Energy Source • Photosynthesizers get energy from the sun • Animals get energy second- or third-hand from plants or other organisms • Regardless, the energy is converted to the chemical bond energy of ATP

6. Making ATP • Plants make ATP during photosynthesis • Cells of all organisms (including plants) make ATP by breaking down carbohydrates, fats, and protein

7. Aerobic pathways Evolved later Require oxygen Start with glycolysis in cytoplasm Completed in mitochondria Anaerobic pathways Evolved first Don’t require oxygen Start with glycolysis in cytoplasm Completed in cytoplasm Main Types of Energy-Releasing Pathways

8. Energy-Releasing Pathways

9. Overview of Aerobic Respiration C6H1206 + 6O2 6CO2 + 6H20 glucose oxygen carbon water dioxide enzymes

10. Main Pathways Start with Glycolysis • Glycolysis occurs in cytoplasm • Reactions are catalyzed by enzymes • ALL LIFEFORMS ON PLANET EARTH Glucose 2 Pyruvate (six carbons) (three carbons)

11. The Role of Coenzymes • NAD+ and FAD accept electrons and hydrogen from intermediates during the first two stages • When reduced, they are NADH and FADH2 • In the third stage, these coenzymes deliver the electrons and hydrogen to the transfer chain (3rd stage)

12. Overview of Aerobic Respiration

13. Glucose • A simple sugar (C6H12O6) • Atoms held together by covalent bonds

14. Glycolysis Occurs in Two Stages • Energy-requiring steps (supply energy) • ATP energy activates glucose and its six-carbon derivatives • Energy-releasing steps (gain energy) • The products of the first part are split into three-carbon pyruvate molecules • ATP and NADH form

15. Net Energy Yield from Glycolysis Energy requiring steps: -2 ATP invested (supply energy) Energy releasing steps: 2 NADH formed 4 ATP formed (gain energy) Net yield is 2 ATP and 2 NADH

16. Second-Stage Reactions(Stage 2) • Occur in the mitochondria • Pyruvate is broken down to carbon dioxide and water • More ATP is formed • More coenzymes are reduced - carry high energy

17. Two Parts of Second Stage • Preparatory reactions (Stage 2a) • Pyruvate is oxidized into two-carbon acetyl units and carbon dioxide • NAD+ is reduced • Krebs cycle (Stage 2b) • The acetyl units are oxidized to carbon dioxide • NAD+ and FAD are reduced

18. Results of the Second Stage • All of the carbon molecules in pyruvate end up in carbon dioxide - released from cells • Coenzymes are reduced (they pick up electrons and hydrogen) - energized • One molecule of ATP is formed - just one!

19. Coenzyme Reductions during First Two Stages - high energy molecules • Glycolysis (stage 1) 2 NADH • Preparatory reactions (stage 2a) 2 NADH • Krebs cycle 2 FADH2 + 6 NADH (stage 2b) • Total 2 FADH2 + 10 NADH

20. Electron Transfer Phosphorylation (chain) • Occurs in the mitochondria • Coenzymes deliver electrons to electron transfer chains • Electron transfer sets up H+ ion gradients • Flow of H+ down gradients powers ATP formation (from between membranes to inner matrix of mitochondria)

21. Second Stage of Aerobic Respiration

22. Electron Transfer Phosphorylation • Electron transfer chains are embedded in inner mitochondrial compartment • NADH and FADH2 give up electrons that they picked up in earlier stages to electron transfer chain • Electrons are transferred through the chain • The final electron acceptor is oxygen

23. Creating an H+ Gradient OUTER COMPARTMENT NADH INNER COMPARTMENT

24. ATP Formation-as the H+ rush back into the mitochondrial matrix they spin a protein that makes lots of ATP ATP INNER COMPARTMENT ADP+Pi

25. Summary of Transfers

26. Importance of Oxygen • Electron transfer chains require the presence of oxygen • Oxygen combines with spent electrons and H+ to form water - which is used by the cell - it is not released from your lungs

27. Summary of Energy Harvest(per molecule of glucose) • Glycolysis step • 2 ATP formed by substrate-level phosphorylation • Krebs cycle and preparatory reactions • 2 ATP formed by substrate-level phosphorylation • Electron transfer phosphorylation • 32 ATP formed

28. Efficiency of Aerobic Respiration • 686 kcal is the about of energy in a glucose molecule • Of the above, 7.5 kcal are conserved in each ATP. When 36 ATP form, 270 kcal (36 X 7.5) are captured in ATP • Efficiency is 270 / 686 X 100 = 39 percent • Most energy (over 60%) is lost as heat

29. What if a cell does not use oxygen? How does it get energy?

30. Anaerobic Pathways • Do not use oxygen • Produce less ATP than aerobic pathways • Two types of fermentation pathways • Alcoholic fermentation - great for students • Lactate fermentation - hurts me

31. Fermentation Pathways • Begin with glycolysis • Do not break glucose down completely to carbon dioxide and water • Yield only the 2 ATP from glycolysis (stage 1) • Steps that follow glycolysis serve only to regenerate NAD+ - no energy is produced

32. Alcoholic Fermentation

33. Yeasts • Single-celled fungi • Carry out alcoholic fermentation • Saccharomyces cerevisiae • Baker’s yeast • Carbon dioxide makes bread dough rise • Saccharomyces ellipsoideus • Used to make beer and wine

34. Lactate Fermentation • Carried out by certain bacteria • No mitochondria, so where does this take place? • Electron transfer chain is in bacterial plasma membrane • Final electron acceptor is compound from environment (such as nitrate), not oxygen • ATP yield is low

35. Lactate Fermentation

36. Carbohydrate Breakdown and Storage • Glucose is absorbed into blood • Pancreas releases insulin (a hormone) • Insulin stimulates glucose uptake by cells • Cells convert glucose to glucose-6-phosphate • This traps glucose in cytoplasm where it can be used for glycolysis

37. Making Glycogen - (this is not glucose) • If glucose intake is high, ATP-making machinery goes into high gear • When ATP levels rise high enough, glucose-6-phosphate is diverted into glycogen synthesis (mainly in liver and muscle) • Glycogen is the main storage polysaccharide in animals

38. Using Glycogen • When blood levels of glucose decline, pancreas releases glucagon (a hormone) • Glucagon stimulates liver cells to convert glycogen back to glucose and to release it to the blood • (Muscle cells do not release their stored glycogen) - selfish ba**ards!!!!!

39. Energy Reserves • Glycogen makes up only about 1 percent of the body’s energy reserves - sugars • Proteins make up 21 percent of energy reserves - proteins • Fat makes up the bulk of reserves (78 percent) - fats

40. Reaction Sites

41. Evolution of Metabolic Pathways • Life started without OXYGEN • Earliest organisms used anaerobic pathways • Then came OXYGEN from some Bacteria • The came organisms with aerobic pathways

42. Aerobic Respiration Reactants Sugar Oxygen Products Carbon dioxide Water Photosynthesis Reactants Carbon dioxide Water Products Sugar Oxygen Cycle of life