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2. Cellular Respiration

2. Cellular Respiration

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2. Cellular Respiration

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  1. But, in the presence of Oxygen…. 2. Cellular Respiration • A series of metabolic pathways involving 3 separate phases: • Krebs cycle • electron transport system • oxidative phosphorylation • Oxidizes pyruvate to ATP & CO2 • Text pg 117 • So why is ATP so important?

  2. ATP Energy released by the oxidation (controlled burning) of carbohydrates and fats, and energy harvested by photosynthesis in green plants, are channeled into making the molecule adenosine triphosphate (ATP). ATP is a high energy compound considered to be the universal currency of biological energy. On reaction of ATP with water under closely controlled conditions, a high energy bond is ruptured releasing energy, and producing adenosine diphosphate (ADP) and phosphate. • This release of energy is usually coupled to other biological processes, to do work, for example, in the contraction of muscle and in the synthesis of the essential macromolecules of life, nucleic acids and proteins. The ATP molecule is then remade from the ADP and phosphate with further input of energy. • The synthesis of ATP is a central process in human nutrition. The energy in the food we ingest is converted into ATP. Each day every one of us of makes, breaks down and remakes in the mitochondria in our bodies an amount of ATP that is about the same as our body weights. The energy in the ATP molecule powers all biological processes. Thus, the synthesis of ATP is essential for life.

  3. Where in the cell does this occur? Mitochondria • double membrane bound organelle • site of aerobic cellular respiration • source of cellular energy

  4. Mitochondria: Structure • Outer membrane • Intermembrane space • Inner membrane (with folds called cristae) • Matrix Text Pg. 68

  5. The Mitochondrion Outer Membrane Intermembrane space Inner Membrane Matrix Cristae

  6. Outer Membrane(& Intermembrane space) • permeable to small molecules (to ~10,000 MW) • contains transmembrane pores (porins) which allow these molecules to pass • composition of intermembrane space closely matches cytoplasm

  7. Inner Membrane • highly folded into “cristae” • folds greatly increase surface area • relatively impermeable to solutes • surface facing matrix lined with small lollipop-like particles (F1 particles)

  8. F1 Particles • about 9 nm in diameter • 10,000 to 100,000 per mitochondria • face matrix side of inner membrane • contain ATP synthase enzyme • couples oxidation reactions with phosphorylation to produce ATP Plant chloroplast F1 particles (ATP synthase) visualized at room temperature using atomic force microscopy

  9. F1 Particles = ATP Synthase • Protein particles which embed in inner mitochondrial membrane and face matrix • Actual site of ATP production in mitochondria F1 F0

  10. Matrix • inner space of mitochondria • rich in proteins • contains ribosomes (70S) and DNA • derived from endosymbiotic prokaryote?? • site of oxidative metabolism (Krebs cycle)

  11. KK KK Krebs Cycle NADH ETC ATP

  12. Glucose Glucose Glycolysis Pyruvate 2 ATP + 2 NADH KK KK Krebs Cycle NADH ATP

  13. Glycolysis: Summary • 10 enzymes act in sequence to: • Convert 1 Glucose (6C) --> 2 Pyruvate (3C) • 2 ATP’s produced • 2 NADH produced • Reactions occur in cytoplasm • Next…

  14. Glucose Glucose Glycolysis Pyruvate 2 ATP + 2 NADH KK KK Krebs Cycle

  15. Pyruvate moves to Mitochondria and is oxidized to Acetyl-CoA

  16. Glycolysis & A-CoA Production 6C glucose 2 NADH 2 ATP In Cytoplasm pyruvate 3C In Mitochondria NADH CO2 Acetyl CoA 2C

  17. Next, Acetyl- CoA enters the Krebs Cycle

  18. Text pg 123

  19. acetyl CoA 2C Oxaloacetate 4C citric acid 6C NADH Krebs Cycle NADH CO2 Malate 4C Fumarate 4C a-Ketoglutarate 5C FADH2 NADH CO2 Succinate 4C Succinyl CoA 4C ATP

  20. Krebs Cycle • Acetyl CoA from pyruvate oxidation is the main input to cycle • A-CoA combines with 4C oxalo-acetate to form 6C citrate • subsequent reactions produce molecules with 5C and 4C… causing the release of CO2 molecules each time • Additionally, these reactions produce NADH, FADH2 and ATP

  21. Krebs Cycle • For each A-CoA going into Krebs… 3 NADH, 1 FADH2, 1 ATP & 2 CO2 are produced • The 2 CO2 molecules released in the cycle convert 6C citrate back to 4C molecules and result in 4C oxaloacetate to renew the cycle • Note: 2 A-CoA are produced for each glucose consumed!

  22. Respiration and ATP How many ATPs have we produced so far from 1 glucose molecule? • 2 ATP from glycolysis • 2 ATP from Krebs Cycle • Both termed substrate-level phosphorylation • Krebs, so far, has doubled ATPs from Glycolysis • But, not over yet..…

  23. Remember the NADH & FADH2 Produced? And, the 2 NADH from Glycolysis

  24. NADH, FADH2 Production in Mitochondria • Each Pyruvate to Acetyl-CoA = 1 NADH 2 Pyruvates (from glucose) = 2NADH • Each Acetyl-CoA in Krebs = 3 NADH & 1 FADH2 2 Acetyl-CoA = 6 NADH & 2 FADH2

  25. Total NADH & FADH2 • 2 NADH from Glycolysis • 2 NADH from Pyr oxidation • 6 NADH from Krebs • Plus: 2 FADH2 from Krebs Cycle

  26. These Energy-Rich Molecules pass on e- to an Electron Transport Chain Along this ETC, new ATP is synthesized from the energy-rich NADH and FADH2 molecules…