Aerobic Respiration & Energy
ProductionDr. Michael P. Gillespie11
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.
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Mitochondria
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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
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Aerobic Respiration
• Aerobic respiration is the oxygen-requiring breakdown of food molecules and production of ATP.
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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.
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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.
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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.
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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.
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Krebs Cycle
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Reaction 1
• 4-Carbon Oxaloacetate combines with Acetyle CoA to yield 5-carbon Citrate and Coenzyme A.
• Citrate Synthase catalyzes this reaction.
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Reaction 2
• Citrate is isomerized to Isocitrate.
• Aconitase catalyzes this reaction in two steps.
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Reaction 3
• Isocitrate is oxidated to α-ketoglutarate.
• CO2 is released.
• NAD+ is reduced to NADH.
• Isocitrate dehydrogenase catalyzes this reaction.
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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.
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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.
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Reaction 6
• Succinate is converted into Fumarate.
• FAD is reduced to FADH2.
• Succinate dehydrogenase catalyzes this reaction.
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Reaction 7
• Fumarate is converted into Malate.
• The enzyme Fumarase catalyzes this reaction.
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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.
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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.
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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
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Important Products From The TCA Cycle
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Krebs Cycle Products
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Krebs Mnemonic
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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.
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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.
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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.
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ATP Yield From Aerobic Respiration
• 2 ATP / glucose from glycolysis
• 34 ATP / glucose from aerobic respiration
• 26 ATP / glucose
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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
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