Cellular Respiration

Principles Module 24

Principles Module 25


  • Describe the 4 major steps that release energy from glucose in the cell
  • Explain the qualities that make ATP an efficient energy-storing molecule

Key points

  • Cellular respiration is the oxidation of organic compounds to extract energy
    • energy is stored in C-C, C-O, and C-H bonds
    • oxidation reactions remove electrons and H+ at same time
  • Overall picture of respiration
    • glucose is oxidized to CO2 and the potential energy is captured by the cell
    • as glucose is oxidized, the electrons are used to reduce an electron carrier, NAD+, to NADH
    • NADH is oxidized by an electron transport chain, resulting in a H+ gradient
    • The H+ gradient is used to drive ATP synthesis
  • ATP as cellular energy
    • stores energy in the 2 terminal phosphate bonds
    • phosphate groups are strongly negative, repel each other
    • requires energy to force them together, gives off energy (–7.3 kcal/mol) when hydrolyzed
  • Four major steps in 2 compartments
    • In the cytoplasm
      • Glycolysis
        • consists of 10 steps
        • yields 4 ATP per glucose by substrate-level phosphorylation
        • yields 2 NADH
        • produces 2 pyruvate molecules
    • In the mitochondria
      • Pyruvate oxidation
        • releases CO2
        • yields 2 NADH
        • produces acetyl-CoA
      • Krebs Cycle (Tricarboxylic Acid Cycle)
        • acetyl-CoA is fully oxidized to CO2
        • an example of a metabolic cycle, in which the initial substrate is regenerated by the pathway itself
        • yields ATP by substrate-level phosphorylation
        • yields NADH and FADH2
      • Electron transport chain and chemiosmosis
        • NADH and FADH2 donate electrons
        • flow of electrons through carrier chain results in the formation of a proton gradient
        • electrons are used to reduce O2 to H2O
        • the proton gradient across the inner membrane drives ATP synthesis

In-class activities

  • Draw a cell and diagram the process of cellular respiration, including the inputs and outputs discussed above.

Questions for Practice

  • List the 4 main steps of cellular respiration and briefly describe each one.
  • Considering cellular respiration as a whole, what is oxidized, and what is reduced?
  • Considering each step of respiration separately, state the effect of a lack of oxygen on each step.
  • Why is ATP a high-energy molecule in the cell? What makes this the case?
  • What is the link between glucose oxidation and ATP synthesis?