9.Pathways That Help Harvest Chemical Energy

9.1

• How do cells obtain energy from glucose?

  • Cells obtain *energy from glucose by the chemical process of oxidation, which is carried out through a series of metabolic pathways.
  • five principles that govern metabolic pathways:
    • A complex chemical transformation occurs in a series of separate reactions that form a metabolic pathway.
    • Each reaction is catalyzed by a specific enzyme.
    • Many metabolic pathways are similar in all organisms, from bacteria to humans.
    • In eukaryotes, many metabolic pathways are compartmentalized, with certain reactions occurring inside specific organelles, or even specific regions of an organelle.
    • Some key enzymes in each metabolic pathway can be inhibited or activated to alter the rate of the pathway.
  • If glucose is burned in a flame or is in a typical cell, it reacts with oxygen gas (O₂), forming carbon dioxide and water and releasing energy in the form of heat.

  •  The balanced equation for the complete reaction is

    C₆H₁₂O₆ + 6 O₂ → 6 CO₂ + 6 H₂O + free energy (ΔG = –686 kcal/mol)

  • This is an oxidation–reduction reaction (more on this shortly), in which glucose loses electrons (becomes oxidized) and oxygen gains them (becomes reduced).

  • The large standard free energy change (ΔG) is negative, indicating that the overall conversion is highly exergonic and can drive the endergonic formation of a lot of…