Aerobic Respiration & Energy Production

1. Aerobic Respiration & Energy Production Dr. Michael P. Gillespie11

2. Mitochondria • Mitochondria are football-shaped organelles that are roughly the size of a bacterial cell. • They are bound by an outer mitochondrial membrane and an inner mitochondrial membrane. • The space between these membranes is the intermembrane space and the space inside the inner membrane is the matrix space. Dr. Michael P. Gillespie

3. Mitochondria Dr. Michael P. Gillespie

4. Mitochondria • The mitochondria has it’s own genetic information and is able to make some of its own proteins. • Mitochondria grow and multiply in a way that is very similar to simple bacteria. • Mitochondria are most likely the descendants of bacteria that were captured by eukaryotic cells millions of years ago. Approximately 1.5 X 109 years ago. Dr. Michael P. Gillespie

5. Outer Mitochondrial Membrane • The outer mitochondrial membrane has small pores through which small molecules can pass. • The molecules that are oxidized for the production of ATP are small enough to easily enter the mitochondrial membrane. Dr. Michael P. Gillespie

6. Inner Mitochondrial Membrane • The inner membrane is highly folded to create a large surface area. • The folded membranes are known as cristae. • The inner membrane is almost completely impermeable. Dr. Michael P. Gillespie

7. Inner Mitochondrial Membrane • Transport proteins bring specific food molecules into the matrix space. • The protein electron carriers of the electron transport system are embedded within the inner membrane. • ATP synthase is embedded in the membrane. Dr. Michael P. Gillespie

8. Origin Of Mitochondria • Mitochondria are roughly the size of bacteria. • Mitochondria have their own genetic information (DNA). • They make their own ribosomes that are very similar to those of bacteria. • The DNA and ribosomes allow the mitochondria to synthesize their own proteins. • Mitochondria are self-replicating. They grow in size and divide to produce new mitochondria. Dr. Michael P. Gillespie

9. Glucose Utilization • Under anaerobic conditions, glucose is broken down into two pyruvate molecules. • Very little of the stored potential energy in glucose is released from this limited degradation of glucose. • Under aerobic conditions the cells can use oxygen and completely oxidize glucose to CO2 in a metabolic pathway called the citric acid cycle. Dr. Michael P. Gillespie

10. Citric Acid Cycle • Often referred to as the Krebs cycle in honor of Sir Hans Krebs who elucidated the steps of this cyclic pathway. • Also called the tricarboxylic acid (TCA) cycle because several of the early intermediates in the pathway have three carboxyl groups. Dr. Michael P. Gillespie

11. Pyruvate Conversion To Acetyle CoA • When pyruvate enters the mitochondria, it must be converted to a two-carbon acetyl group. • The acetyl group must be activated to enter into Krebs cycle. • It is activated when it is bonded to coenzyme A. • Acetyle CoA is the “activated” form of the acetyl group. Dr. Michael P. Gillespie

12. Pyruvate Conversion To Acetyle CoA • Four coenzymes from four different vitamins are necessary for this reaction to occur. • Thiamine pyrophosphate from thiamine (Vitamin B1) • FAD derived from riboflavin (Vitamin B2) • NAD+ derived from niacin • Coenzyme A derived from pantothenic acid Dr. Michael P. Gillespie

13. Aerobic Respiration • Aerobic respiration is the oxygen-requiring breakdown of food molecules and production of ATP. Dr. Michael P. Gillespie

14. Compartments of Mitochondria • Different steps of aerobic respiration occur in different compartments of the mitochondria. • The enzymes for the citric acid cycle are found in the mitochondrial matrix. Dr. Michael P. Gillespie

15. Compartments of Mitochondria • Electrons from NADH and FADH2 are passed through the electron transport system located in the inner mitochondrial membrane. • This transfer of electrons causes protons to be pumped out of the mitochondrial matrix into the intermembrane compartment (resulting in a high energy H+ reservoir. Dr. Michael P. Gillespie

16. Compartments of Mitochondria • The high energy H+ reservoir is used to make ATP. The enzyme ATP synthase facilitates this step. • The protons flow back into the mitochondrial matrix through a pore in the ATP synthase complex and ATP is generated. Dr. Michael P. Gillespie

17. The Citric Acid Cycle • The citric acid cycle is the final stage of the breakdown of carbohydrates, fats, and amino acids. • The following steps will follow the acetyl group of an acetyle CoA as it passes through the citric acid cycle. • Pyruvate was converted to acetyl CoA when it entered the mitochodria, thus preparing it for entry into Krebs cycle. Dr. Michael P. Gillespie

18. Krebs Cycle Dr. Michael P. Gillespie

19. Reaction 1 • 4-Carbon Oxaloacetate combines with Acetyle CoA to yield 5-carbon Citrate and Coenzyme A. • Citrate Synthase catalyzes this reaction. Dr. Michael P. Gillespie

20. Reaction 2 • Citrate is isomerized to Isocitrate. • Aconitase catalyzes this reaction in two steps. Dr. Michael P. Gillespie

21. Reaction 3 • Isocitrate is oxidated to α-ketoglutarate. • CO2 is released. • NAD+ is reduced to NADH. • Isocitrate dehydrogenase catalyzes this reaction. Dr. Michael P. Gillespie

22. Reaction 4 • 5-carbon α-ketoglutarate is converted to 4-carbon Succinyl CoA. • A carboxylate group is lost in the form of CO2. • NAD+ is reduced to NADH. • The enzyme α-ketoglutarate dehydrogenase catalyzes this reaction. • Coenzyme A assists. Dr. Michael P. Gillespie

23. Reaction 5 • Succinyl CoA is converted to Succinate. • An inorganic phosphate is added to GDP to create GTP. • The enzyme Succinyl CoA synthase catalyzes this reaction. • Coenzyme A is restored. • Dinucleotide diphosphokinase transfers a phosphoryl group from GTP to ADP to make ATP. Dr. Michael P. Gillespie

24. Reaction 6 • Succinate is converted into Fumarate. • FAD is reduced to FADH2. • Succinate dehydrogenase catalyzes this reaction. Dr. Michael P. Gillespie

25. Reaction 7 • Fumarate is converted into Malate. • The enzyme Fumarase catalyzes this reaction. Dr. Michael P. Gillespie

26. Reaction 8 • Malate is converted back into Oxaloacetate. • The citric acid cycle began with this product so we have come full circle. • NAD+ is reduced to NADH. • Malate dehydrogenase catalyzes this reaction. Dr. Michael P. Gillespie

27. Dr. Michael P. Gillespie

28. Point to Remember • Recall that for every glucose molecule that was degraded in glycolysis, two molecules of pyruvate were created. • Therefore, two turns of the TCA cycle happen for every molecule of glucose. Dr. Michael P. Gillespie

29. Important Products From The TCA Cycle • Per turn of the TCA cycle • 1 ATP • 3 NADH • 1 FADH2 • Per glucose molecule • 2 ATP • 6 NADH • 2 FADH2 Dr. Michael P. Gillespie

30. Important Products From The TCA Cycle Dr. Michael P. Gillespie

31. Krebs Cycle Products Dr. Michael P. Gillespie

32. Krebs Mnemonic Dr. Michael P. Gillespie

33. Oxidative Phosphorylation • Electrons carried by NADH can be used to produce three ATP molecules. • Electrons carried by FADH2 can be used to produce two ATP molecules. Dr. Michael P. Gillespie

34. Oxidative Phosphorylation • Electron transport systems are embedded within the mitochondrial inner membrane. • These electron carriers pass electrons from one carrier in the membrane to the next. • Protons (H+) can be pumped from the mitochondrial matrix to the intermembrane space at three sites in the electron transport system. Dr. Michael P. Gillespie

35. Oxidative Phosphorylation • At each site, enough H+ are pumped into the H+ reservoir to produce one ATP molecule. • A multiprotein complex called ATP synthase catalyzes the phosphorylation of ADP to produce ATP. • There is a channel in the ATP synthase through which H+ pass. The energy of the flow of H+ is harvested to make ATP. Dr. Michael P. Gillespie

36. ATP Yield From Aerobic Respiration • 2 ATP / glucose from glycolysis • 34 ATP / glucose from aerobic respiration • 26 ATP / glucose Dr. Michael P. Gillespie

37. ATP Yield From Aerobic Respiration • Glycolysis • Substrate level phosphorylation – 2 ATP • 2 NADH X 2 ATP / cytoplasmic NADH – 4 ATP • Conversion of 2 pyruvate molecules to 2 acetyl CoA molecules • 2 NADH X 3 ATP / NADH – 6 ATP • Citric Acid Cycle (2 Turns) • 2 GTP X 1 ATP / GTP – 2 ATP • 6 NADH X 3 ATP / NADH – 18 ATP • 2 FADH2 X 2 ATP / FADH2 – 4 ATP • 36 ATP Total Dr. Michael P. Gillespie