Respiration

• Cellular Respiration


  The process by which living cells convert chemical energy from nutrients into ATP, the universal energy currency of cells

  
• Cellular Respiration


  1. Glycolysis

  2. Link Reaction

  3. TCA Cycle

  4. Electron Transport

  
• Metabolism


  The sum total of the biochemical reactions that take place within an organism, including reactions that allow energy to be stored, transferred or released, and reactions that synthesize and break down important carbon molecules

  
• Metabolic Reactions


  • Anabolic (Synthesis)
  • Catabolic (Breakdown)
• ATP


  The form of chemical energy available at the biochemical level, built up from ADP and phosphate
• Metabolic Processes all involve ATPase enzymes, which catalyze the breakdown of ATP to ADP + Pi, and make use of the energy released

  
• ATP molecules in a cell are constantly being cycled between ATP and ADP + Pi
• Glycolysis


  A pathway found in almost all organisms, where a small amount of energy is captured as a glucose molecule is converted to two molecules of pyruvate

  
• Glycolysis


  • Occurs in the cytoplasm
  • Converts a 6C sugar (glucose) to 2 3C compounds (Pyruvate)

  
• Aerobic Glycolysis


  Sets the stage for the oxidative decarboxylation of pyruvate to acetyl CoA, a major fuel of the TCA cycle

  
• Anaerobic Glycolysis


  Pyruvate is reduced to lactate/alcohol production

  
• Na+-independent, facilitated diffusion transport system

  An energy-requiring process that transports glucose "against" the concentration gradient, from low glucose concentrations outside the cell to higher concentrations within the cell

  
• Na+-monosaccharide cotransporter system


  A carrier-mediated process in which the movement of glucose is coupled to the concentration gradient of Na+

  
• Glycolysis


  1. Energy investment phase (ATP provides activation energy by phosphorylating glucose)

  2. Energy payoff phase (ATP is produced by substrate-level phosphorylation and NAD+ is reduced to NADH)
• Phosphorylated sugar molecules do not readily penetrate cell membranes, as there are no specific trans-membrane carriers for these compounds
• Substrate level phosphorylation


  Phosphorylation of ADP to ATP at the reaction site
• ATP made during glycolysis is generated by substrate level phosphorylation

  
• The reactions of glycolysis take place within the cytosol of eukaryotic cells
• Oxidative decarboxylation of pyruvate


  Irreversibly converts pyruvate to acetyl CoA, a major fuel for the TCA cycle

  
• Reduction of pyruvate


  Lactate fermentation (animals) or Alcoholic Fermentation (microorganisms and plants) when O2 is absent

  
• After Glycolysis which takes place in the cytosol, all the steps of cellular respiration take place in the mitochondria

  
• Link Reaction


  Oxidation, Decarboxylation, and attachment of CoA to acetate to form Acetyl CoA

  
• Krebs Cycle


  A metabolic pathway that is amphibolic (both catabolic and anabolic), cyclic, and produces reduced NAD and FAD which are precursors to ATP, as well as CO2 as an excretory product

  
• Oxidative Phosphorylation


  1. Oxidation step: electron transport chain

  2. Phosphorylation step: ADP + Pi -> ATP

  
• Electron Transport Chain


  The process that couples electron transport to ATP synthesis via chemiosmosis, using the energy released from the oxidation of NADH and FADH2

  
• The energy released during electron transport is used to transport protons (H+) from the mitochondrial matrix to the intermembrane space, where a high concentration of protons accumulates
• The protons cannot diffuse back into the matrix except through special channels in ATP synthase in the inner membrane
• The flow of the protons through the ATP synthase channels powers the synthesis of ATP

  
• Oxidation step


  Electron transport chain
• NADH


  Carries electrons from food
• NAD+


  Oxidized form of NADH
• FADH2


  Carries electrons from food
• FAD


  Oxidized form of FADH2
• Electron Transport Chain


  1. During oxidative phosphorylation, chemiosmosis couples electron transport to ATP synthesis

  2. Following glycolysis and the citric acid cycle, NADH and FADH2 account for most of the energy extracted from food

  3. NADH and FADH2 accepted electrons and at least one proton

  4. These two electron carriers donate electrons to the electron transport chain, which powers ATP synthesis via oxidative phosphorylation

  
• Electron Transport Chain


  1. During electron transport, The energy released during electron transport is used to transport protons (H+) from the mitochondrial matrix to the intermembrane space, where a high concentration of protons accumulates

  2. The protons cannot diffuse back into the matrix except through special channels in ATP synthase in the inner membrane

  3. The flow of the protons through ATP synthase provides the energy for generating ATP from ADP and inorganic phosphate (Pi )

  4. In the process, the inner part of ATP synthase rotates (thick red arrows) like a motor

  5. Protons which have travelled through the ATP synthesase molecule will then combine with the electrons to form Hydrogen; which in turn couples with Oxygen to form H2O

  
• Electron Transport Chain


  • The electron transport chain is in the cristae of the mitochondrion
  • Most of the chain's components are proteins, which exist in multi-protein complexes numbered I through IV
  • The carriers alternate reduced and oxidized states as they accept and donate electrons
  • What happens, a carrier accepts an electron then hands it down to the next carrier
  • Electrons drop in free energy as they go down the chain and released energy is used to pump protons from the matrix across the inner mitochondrial membrane to the intermembrane space
  • The energy stored in a H+ gradient across a membrane couples the redox reactions of the electron transport chain to ATP synthesis
  • The H+ gradient is referred to as a proton-motive force, emphasizing its capacity to do work
• During cellular respiration, most energy flows in this sequence: glucose NADH and FADH2 electron transport chain proton-motive force ATP

  
• About 40% of the energy in a glucose molecule is transferred to ATP during cellular respiration, making about 38 ATP

  
• Anaerobic respiration


  Enables cell to produce energy without O2
• Glycolysis


  Can produce ATP with or without O2 (in aerobic or anaerobic conditions)