3.5 Cellular Respiration

Describe the processes and structural features of mitochondria that allow organisms to use energy stored in biological macromolecules.

• Cellular respiration uses energy from biological macromolecules to synthesize ATP. Respiration and fermentation are characteristic of all forms of life.
• Aerobic cellular respiration in eukaryotes involves a series of coordinated enzymecatalyzed reactions that capture energy from biological macromolecules.
• The ETC transfers electrons in a series of oxidation-reduction reactions that establish an electrochemical gradient across membranes.
  • i. In cellular respiration, electrons delivered by NADH and FADH2 are passed to a series of electron acceptors as they move t oward the terminal electron acceptor, oxygen. Aerobic prokaryotes use oxygen as a terminal electron acceptor, while anaerobic prokaryotes use other molecules.
  • Exclusion: The full names of the specific electron carriers in the electron transport chain are beyond the scope of the AP Exam. Specific steps, names of enzymes, and intermediates of the pathways for these processes are beyond the scope of this course and the AP Exam.

Explain how cells obtain energy from biological macromolecules in order to power cellular functions.

• Glycolysis is a biochemical pathway that releases the energy in glucose molecules to form ATP (from ADP and inorganic phosphate), NADH (from NAD+), and pyruvate.
• Pyruvate is transported from the cytosol to the mitochondrion where oxidation occurs. This process releases electrons during the Krebs (citric acid) cycle, reducing NAD+ to NADH and FAD to FADH2, and releasing CO2 . 77 Cellular Energetics UNIT 3
• The Krebs cycle takes place in the mitochondrial matrix. During the Krebs cycle, carbon dioxide is released from organic intermediates, ATP is synthesized from ADP and inorganic phosphate, and electrons are transferred by the coenzymes NAD+ and FAD.
• Electrons extracted in glycolysis and Krebs cycle reactions are transferred by NADH and FADH2 to the ETC in the inner mitochondrial membrane.
• When electrons are transferred between molecules in a sequence of reactions as they pass through the ETC, an electrochemical gradient of protons (hydrogen ions) across the inner mitochondrial membrane is established. The pH inside the mitochondrial matrix is higher than in the intermembrane space.
• Fermentation allows glycolysis to proceed in the absence of oxygen and produces organic molecules such as alcohol and lactic acid.
• Exclusion: Memorization of the steps in glycolysis and the Krebs cycle, and of the structures of the molecules and the names of the enzymes involved, is beyond the scope of this course and the AP Exam.