Chapter 9: Pathways That Harvest Chemical Energy

• What is the main topic of Chapter 9?

  Pathways That Harvest Chemical Energy
• What are the key concepts covered in Chapter 9?

  • Cells harvest chemical energy from glucose oxidation
  • Glucose is fully oxidized in the presence of oxygen
  • Oxidative phosphorylation forms ATP
  • Energy is harvested from glucose in the absence of oxygen
  • Metabolic pathways are interrelated and regulated
• What is the role of brown fat in human infants?

  It releases energy as heat to keep the baby warm.
• How are mitochondria related to obesity?

  Mitochondria in brown fat help regulate energy expenditure.
• How do cells obtain energy from glucose?

  Through a series of metabolic pathways.
• What are the five principles of metabolic pathways?

  1. Complex transformations occur in a series of separate reactions.
  2. Each reaction is catalyzed by a specific enzyme.
  3. Many metabolic pathways are similar in all organisms.
  4. Metabolic pathways are compartmentalized in specific organelles in eukaryotes.
  5. Key enzymes can be inhibited or activated to alter the rate of the pathway.
• What is the chemical equation for the burning of glucose?

  $C_6H_{12}O_6 +$$6 O_2 \rightarrow 6 CO_2 +$$6 H_2O +$$\text{free energy}$
• What does the ΔG value of -686 kcal/mol indicate about glucose metabolism?

  It is highly exergonic and drives the formation of ATP.
• What are the three catabolic processes that harvest energy from glucose?

  1. Glycolysis (anaerobic)
  2. Cellular Respiration (aerobic)
  3. Fermentation (anaerobic)
• What are oxidation-reduction (redox) reactions?

  They involve the transfer of electrons between substances.
• What happens during reduction in redox reactions?

  There is a gain of electrons.
• What happens during oxidation in redox reactions?

  There is a loss of electrons.
• In glucose metabolism, what is the reducing agent?


  Glucose is the reducing agent.
• In glucose metabolism, what is the oxidizing agent?

  Oxygen is the oxidizing agent.
• What does the transfer of electrons often associate with?

  It is often associated with the transfer of hydrogen ions.
• What is the role of coenzyme NAD⁺ in redox reactions?

  It is a key electron carrier.
• What happens during the reduction of NAD⁺?

  NAD⁺ + H⁺ + 2e^- → NADH
• What happens during the oxidation of NADH?

  NADH + H⁺ + ½ O₂ → NAD⁺ + H₂O
• What is the ΔG value for the oxidation of NADH?

  ΔG = -52.4 kcal/mol
• What is the role of oxygen in aerobic conditions?

  Oxygen is the final electron acceptor.
• What are the steps of glycolysis?

  1. Takes place in the cytoplasm.
  2. Converts glucose into 2 molecules of pyruvate.
  3. Produces 2 ATP and 2 NADH.
  4. Occurs in 10 steps.
• What are the two types of reactions in metabolic pathways?

  Oxidation-reduction and substrate-level phosphorylation.
• Where does pyruvate oxidation occur?

  In the mitochondrial matrix.
• What happens to pyruvate during pyruvate oxidation?

  It is oxidized to acetate and CO₂.
• What is formed when acetate binds to coenzyme A?

  Acetyl CoA is formed.
• What is the role of the pyruvate dehydrogenase complex?

  It catalyzes the three intermediate steps in pyruvate oxidation.
• What is the starting point of the citric acid cycle?

  Acetyl CoA is the starting point.
• What occurs during the citric acid cycle?

  • Acetyl CoA is completely oxidized to 2 molecules of CO₂.
  • Eight reactions capture energy by GDP, NAD⁺, and FAD.
  • Oxaloacetate is regenerated in the last step.
• What is the overall yield from the oxidation of one glucose molecule in the citric acid cycle?

  6 CO₂, 10 NADH, 2 FADH₂, and 4 ATP.
• What must happen for the citric acid cycle to continue?

  The starting molecules must be replenished and electron carriers reoxidized.
• What happens to electrons in the presence of oxygen?

  Oxygen accepts the electrons and water is formed.
• What is oxidative phosphorylation?

  • ATP is synthesized by reoxidation of electron carriers in the presence of O₂.
  • It involves two components: electron transport and chemiosmosis.
• What occurs during electron transport in oxidative phosphorylation?

  Electrons from NADH and FADH₂ pass through the respiratory chain.
• What is created as a result of electron flow during electron transport?

  A proton concentration gradient across the inner mitochondrial membrane.
• What is chemiosmosis in oxidative phosphorylation?

  It is the process where protons flow back across the membrane through ATP synthase, coupling diffusion with ATP synthesis.
• What happens to protons during electron transport?

  Protons are actively transported into the intermembrane space.
• What is the proton-motive force?

  It is the potential energy created by the proton concentration and charge difference across the membrane.
• How does ATP synthase function in oxidative phosphorylation?

  It couples the diffusion of protons back into the matrix with ATP synthesis.
• What additional role can ATP synthase perform?

  It can act as ATPase, hydrolyzing ATP to ADP.
• What do FADH₂ molecules pass through in the respiratory chain?

  Membrane-associated carriers