Stages of Cellular Respiration and Fermentation

1. Stages of Cellular Respiration and Fermentation There are three that occur continuously

2. Overview • First two (Glycolysis and Krebs) are exergonic • Break down glucose and other organic fuels • Glycolysis occurs in the cytoplasm • Begins respiration by breaking glucose into 2 molecules of pyruvic acid • Krebs Cycle occurs in the mitochondria • Completes breakdown of glucose by decomposing a pyruvic acid derivative into Carbon Dioxide • The cell makes a small amount of ATP during these two stages • The main function of these two stages is to provide electrons to the third stage of respiration

3. 3rd Stage is the Electron Transport Chain • Obtains electrons from NADH(the reduced form of NAD), as well as from FADH2 (the reduced form of FAD) • This process stores energy that ATP Synthase enzyme uses to make most of the cell’s ATP by chemiosmosis

4. Overview of Respiration

5. Glycolysis: Harvesting Chemical Energy • “splitting of sugar” • Universal energy-harvesting process- all living cells (an ancient process) • Begins with a single molecule of sugar • 6-Carbon sugar • Ends with two molecules of pyruvic acid • Each has 3-Carbon sugar • As the reaction occurs it releases two molecules of ATP by substrate-level phosphorylation and reduces two molecules of NAD to NADH • Thus, banking energy in ATP and NADH

6. Glycolysis Breakdown • Between glucose and the pyruvic acids there are intermediates(which you won’t need to know in Honors Bio). • Each chemical step leads to the next in succession • Starting materials: glucose (fuel), ADP and inorganic phosphate, and NAD • Along with a little ATP- thus the cell must expend a little energy to start glycolysis • Plus a few needed enzymes

7. Glycolysis continued… • 2 sets of stages • First is preparatory and consumes energy • ATP energy(2 molecules) is used to split glucose into two smaller ones • Second is energy yielding. • Because there are two pyruvic acids, all of these stages occur in duplicate. • NADH is produced along with the oxidation of sugar, and 4 ATP are produced. • Thus, the net gain of ATP during Glycolysis is 2 ATP per molecule of glucose • Accounts for 5% of the energy that a cell can harvest from a molecule of glucose • NADH in 2 set of stages account for an additional 16% of potential ATP • Most organisms need a lot more energy than that!

8. Glycolysis

9. Details of Glycolysis-which you do not need to know in Honors Biology

10. Pyruvic Acids get “groomed” for the Krebs Cycle • Pyruvic acid diffuses through cytoplasm into the mitochondria • It is oxidized while NAD+ is reduced to NADH • A carbon atom is removed/released as CO2 • Coenzyme A (from B vitamin) joins with the 2-Carbon molecule remaining to form acetyl coenzyme A (acetyl CoA) • Fuel molecule for the Krebs cycle • For each molecule of glucose that entered glycolysis, two molecules of acetyl-CoA enter the Krebs Cycle

11. Preparation for Krebs

12. Krebs Cycle • Coenzyme A helps the acetyl enter into the Krebs cycle and then splits and is recycled • Only the 2-C acetyl enters • Each step is catalyzed by a specific enzyme • Disassembles acetyl CoA • Strips its electrons • Casts off 2 Carbons as CO2 per acetyl fragment that enters into the Krebs cycle

13. Krebs Cycle Continued… • Each turn of the cycle yields one molecule of ATP by substrate level phosphorylation • Also yields 3 NADH molecules and one molecule of FADH2 molecule • Since there are two acetyl CoA molecules per glucose molecule, the actual yield is: 2ATP, 6 NADH, and 2FADH2 • By this point, the cell has gained a total of 4 ATP, 10 NADH and 2 FADH2 • To actually use all of this energy, the cell must transfer all of the energy in the NADH and FADH2 to ATP

14. Krebs Cycle - you need to know diagram on left but not the details on right for Honors Biology • .

15. Chemiosmosis powers most ATP production • Final stage: ETC and ATP synthesis by chemiosmosis • With chemiosmosis, the spatial arrangement of membrane bound proteins makes it possible for mitochondria to use chemical energy to create a H+ gradient • Can then use energy stored in the gradient to drive ATP synthesis

16. Chemiosmosis in the Membrane

17. The how, where, and why • ETC of cellular respiration is in the inner membranes of the mitochondria. • Cristae (folds of the membrane) extend its surface area. • Many copies of ETC and many ATP synthase complexes • Can produce many ATP simultaneously • Path: NADHETC O2 • Each oxygen atom combines with 2 electrons and 2 hydrogens to form H2O ( one of the final products of cellular respiration) • All carriers bind and release electrons in redox reactions.

18. What happens when redox occurs? • Use energy released from electrons to move H+ across the membrane from the matrix into the innermembrane space. • The resulting H+ gradient stores potential energy • Ready to produce a LOT of ATP • ATP Synthase provides the channel to allow H+ ions through • Contains the enzyme necessary to catalyze the phosphorylation of ADP to ATP • As H+ ions pass through, they drive ATP synthesis

19. Finally • Via Chemiosmosis, the cell can couple the exergonic reactions of the ETC to the endergonic formation of ATP. • The total net yield of ATP per glucose molecule has a maximum of 38. • This can be interfered with, ie. Certain poisons or toxins • See additional notes and diagrams on this info • Without O2, chemiosmosis cannot occur. What then???

20. ATP Yield – when everything works the way it should

21. Poisons that can block the ETC – ATP formation is blocked at different steps by different toxins

22. Anaerobic alternatives • Some organisms, like yeast and bacteria can survive without oxygen. They use only the 2 ATP generated from glycolysis • But how can they replenish the NAD+ from its reduced form? • Use Fermentation!

23. Types of Fermentation • Alcoholic Fermentation • Can convert pyruvic acids to CO2 and ethyl alcohol • Yeasts release alcoholic wastes into the environment, but die if the alcohol becomes too concentrated • Lactic Acid Fermentation • Produces lactic acid when NADH is oxidized • No CO2 is produced • Used in dairy industry- cheese and yogurt • If you get a “stitch” when you exercise, lactic acid causing it can be broken down by liver to end muscle cramp

24. Fermentation

25. Oxygen-lacking conditions • Strict Anaerobes • Require anaerobic conditions • Oxygen is poisonous • Facultative anaerobes (E.coli) can make ATP by fermentation or chemiosmosis depending upon conditions

26. Cells use all kinds of organic food sources

27. Also use other foods for biosynthesis

28. So why do we usually use glucose to fuel cell respiration? • Fat gives us twice as much ATP as an equal amount of starch, but we must use as much energy to break it down as it gave us in storage. It’s easier for our cells to break down carbohydrates into glucose and use those, so our body goes for those first!

29. But where does all of this food come from? • Photosynthesis • Time to reverse the reaction!

30. Let’s Review – 10 questions!

31. Question • The break down of glucose is called • Hydrolysis • Cytolysis • Dehydration synthesis • glycolysis

32. Question 2. The resulting products of glycolysis include • Sugar • ATP • ADP • water

33. Question 3. NAD and FAD molecules move the following throughout the cell • Electrons • Hydrogens • Energy • All of the above

34. Question 4. The organic product of glycolysis is a molecule containing ___ carbon atoms called pyruvic acid • One • Two • Three • Four

35. Question 5. Pyruvic acid is formed in the cells _____. • Matrix • Stroma • Cytoplasm • Membrane

36. Question 6. After grooming pyruvic acid enters into the second stage of aerobic cellular respiration aka ___. • Krebs Cycle • Electron Transport chain • Substrate level phosphorylation • Chemiosmosis

37. Question 7. The Krebs cycle takes place in the ___of the mitochondria. • Inter-membrane space • Outer membrane • Inner membrane • Matrix

38. Question 8. The products of the Krebs cycle include • ATP • NADH and FADH2 • CO2 • All of the above

39. Question 9. Chemiosmosis generates more ATP than glycolysis because of the presence of • The electron transport chain • Oxygen • ATP synthase • All of the above

40. Question 10. Glycolysis is an ___ process • Aerobic • Anaerobic