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Ch 9- Cellular Respiration

Ch 9- Cellular Respiration. How do we get the energy we need? Food What in food gives us the energy we need? Cellular Respiration- process that releases energy by breaking down food molecules in the presence of oxygen Made up of glycolysis , Krebs cycle, and the electron transport chain

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Ch 9- Cellular Respiration

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  1. Ch 9- Cellular Respiration • How do we get the energy we need? • Food • What in food gives us the energy we need? • Cellular Respiration- process that releases energy by breaking down food molecules in the presence of oxygen • Made up of glycolysis, Krebs cycle, and the electron transport chain • Equation for cellular respiration • 6 O₂+ C₆H₁₂O₆→ 6 CO₂+ 6 H₂O + Energy

  2. Main Stages of Cellular Respiration • Each stage captures some of the chemical energy available in food molecules and uses it to produce ATP • Glycolysis- process in which one molecule of glucose is broken in half, producing two molecules of pyruvic acid- 3-carbon compound • Glycolysis needs 2 ATP molecules to begin process • What happens during glycolysis? • 2 molecules of pyruvic acid, 2 molecules of ATP, and 2 molecules of NADH are produced • One of reactions of glycolysis removes 4 high energy electrons and passes them to NAD⁺-electron carrier • Each NAD⁺ accepts a pair of high energy electrons and transfers them to other molecules • Allows energy from glucose to be passed to other pathways in cell • Cellular Respiration

  3. Fermentation • Releases energy from food molecules by producing ATP in the absence of oxygen • What happens during fermentation? • NADH is converted back to NAD⁺ by passing high energy electrons back to pyruvic acid • Allows glycolysis to produce steady supply of ATP • Anaerobic • 2 main types of fermentation- alcoholic fermentation and lactic acid fermentation

  4. Alcoholic fermentation- uses pyruvic acid and NADH to produce ethyl alcohol, carbon dioxide and NAD⁺ • Used by yeasts and few other microorganisms • Lactic Acid- uses pyruvic acid and NADH to produced lactic acid and NAD⁺ • Produced in muscles during rapid exercise when body cannot supply enough oxygen to tissues • Unicellular organisms produce lactic acid as waste, as result prokaryotes are used in array of food production

  5. Sec 2- Krebs Cycle and Electron Transport • 90% of chemical energy still available in glucose after glycolysis, locked up in high energy electrons of pyruvic acid • Oxygen is required for final steps of cellular respiration- aerobic

  6. Krebs Cycle • Oxygen must be present • Also known as Citric Acid Cycle • During cycle, pyruvic acid is broken down into carbon dioxide in a series of energy extracting reactions • Citric Acid Production • Pyruvic acid enters mitochondrion, carbon is removed forming CO₂, electrons are removed, changing NAD⁺ to NADH • Coenzyme A joins the 2 carbon molecule, forming acetyl- CoA. Acetyl- CoA adds the 2 carbon acetyl group to a 4-carbon compound forming citric acid

  7. Energy Extraction • Citric acid is broken down into 5-carbon compound and then into 4-carbon compound • 2 more molecules of CO₂ are released and electrons join NAD⁺ and FAD, forming NADH and FADH₂, one molecule of ATP is generated • Energy output from one molecule of pyruvic acid= 4 NADH, 1 FADH₂, and 1 molecule of ATP • CO₂ released is source of all carbon dioxide we breathe • ATP produced in Krebs cycle is used for cellular activities

  8. Electron Transport Chain • Krebs cycle generates high energy electrons that are passed to NADH and FADH₂ • Electrons are passed from carriers to electron transport chain • Uses high energy electrons from Krebs cycle to convert ADP to ATP • Takes place in mitochondrion • Steps of Electron Transport Chain • High energy electrons passed along chain from one carrier protein to next. At end of chain, enzyme combines these electrons with hydrogen ions and oxygen to form water • Oxygen serves as final acceptor, it is essential for getting rid of low energy electrons and hydrogen ions-the wastes of cellular respiration

  9. Every time 2 high energy electrons transport down chain, energy is used to transport hydrogen ions across the membrane • Inner membrane of mitochondria contain protein spheres called ATP synthases, as H⁺ ions escape through channels, into these proteins, ATP synthases spin and grab a low energy ADP and attaches a phosphate, forming high energy ATP • On average, each pair of high energy electrons produces 3 molecules of ATP from ADP

  10. Totals • Glycolysis produces 2 ATP molecules • Krebs cycle and Electron Transport Chain produce roughly 36 ATP molecules, 18 times more than glycolysis

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