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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
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
main stages of cellular respiration
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
  • 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

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
sec 2 krebs cycle and electron transport
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
krebs cycle
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

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
electron transport chain
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

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