chapter 9

• Catabolic pathways


  Release stored energy by breaking down complex molecules (exergonic)
• Catabolic pathways


  • Aerobic respiration
  • Anaerobic respiration
  • Fermentation
• Aerobic respiration


  Consumes organic molecules & O2 to yield ATP
• Anaerobic respiration


  Consumes organic molecules to yield ATP without O2 (Alt electron acceptor required)
• Fermentation


  Partial degradation of sugars that occurs without O2
• Cellular Respiration


  C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + Energy
• Cellular Respiration


  Energy produced is in the form of ATP and heat (exergonic)
• Fuels for cellular respiration


  • Carbohydrates
  • Lipids
  • Proteins
• Potential energy


  Stored in arrangement of e- in bonds between atoms
• Principles of metabolic pathways


  • Complex transformations occur in a series of separate reactions
  • Each reaction is catalyzed by a specific enzyme
  • Many metabolic pathways are similar in all organisms
  • In eukaryotes, metabolic pathways are compartmentalized in specific organelles
  • Key enzymes can be inhibited or activated to alter the rate of the pathway
• Oxidation


  A substance loses electrons
• Reduction


  A substance gains electrons
• Reducing agent


  The electron donor
• Oxidizing agent


  The electron receptor
• Oxidation and reduction are coupled
• During cellular respiration, the fuel (such as glucose) is oxidized, and O2 is reduced</b>
• Glucose is broken down in a series of steps


  At key steps, electrons are stripped from glucose, in the form of a Hydrogen atom [H = H+ + e-]
• Loss of H atoms

  Creates oxidized molecule
• Electrons are usually first transferred to an electron acceptor


  NAD+ or FAD
• NADH/FADH2


  Represents stored energy that can be used to synthesize ATP
• The ultimate fate of the NADH or FADH2 molecules is to transfer their electrons (stored energy) to oxygen, O2
• O2 accepts electrons from NADH

  O2 is the oxidizing agent
• Substrate level phosphorylation


  Involves the direct transfer of a phosphate group
• Stages of aerobic cellular respiration


  • Glycolysis
  • Citric acid cycle
  • Oxidative phosphorylation
• Fermentation


  Uses substrate-level phosphorylation instead of an electron transport chain to generate ATP
• Cellular locations for major energy pathways in eukaryotes and prokaryotes


  • Glycolysis
  • Citric acid cycle
  • Oxidative phosphorylation
• Glycolysis


  1. Breaks down glucose into two molecules of pyruvate

  2. Energy investment phase (steps 1-5)

  3. Energy payoff phase (steps 6-10)
• Glycolysis


  • Occurs in the cytoplasm
  • Occurs with or without O2
• Net yield of glycolysis


  2 ATP + 2 NADH + 2 Pyruvate
• Pyruvate oxidation


  1. Occurs in the mitochondrial matrix

  2. Produces acetate and CO2

  3. Acetate binds to coenzyme A to form acetyl CoA

  4. Catalyzed by the pyruvate dehydrogenase complex
• Pyruvate oxidation


  Exergonic; one NAD+ is reduced to NADH
• Citric acid cycle


  1. Acetyl CoA is the starting point

  2. The acetyl group is completely oxidized to 2 molecules of CO2

  3. Energy released is captured by ADP, NAD+, FAD, and GDP
• Net yield of citric acid cycle

  4 CO2 + 2 ATP + 6 NADH + 2 FADH2
• Oxidative phosphorylation


  Electron transport chain + Chemiosmosis
• Electron transport chain


  1. Electrons from NADH and FADH2 pass through the respiratory chain of membrane-associated carriers

  2. Electron flow results in a proton concentration gradient across the inner mitochondrial membrane
• Chemiosmosis


  Uses energy stored in H+ gradient across a membrane to synthesize ATP
• ATP synthase


  A membrane channel protein that couples the diffusion of H+ into cell with ATP synthesis
• The respiratory chain is located in the folded inner mitochondrial membrane
• Electron transport chain


  • Located in the inner mitochondrial membrane of the mitochondrion
  • NADH/FADH2 harbor most of the energy
  • Electrons drop in free energy as they go down the chain
  • Electrons are finally passed to O2 to form H2O
• Electron transport chain and chemiosmosis

  1. Protons are actively transported during ETC

  2. H+ accumulate in the intermembrane space of mitochondria

  3. This creates a concentration gradient & charge difference (Potential Energy Source)

  4. H+ flow back across membrane by passing through ATP synthase