Key Concepts of Cellular Respiration Process to Know for AP Biology

Cellular respiration is how cells convert glucose into energy. This process includes glycolysis, the Krebs cycle, and the electron transport chain, ultimately producing ATP. Understanding this process is key in AP Biology, as it highlights energy flow in living organisms.

1. Glycolysis

   • Occurs in the cytoplasm and breaks down glucose into two molecules of pyruvate.
   • Produces a net gain of 2 ATP and 2 NADH molecules.
   • Does not require oxygen, making it an anaerobic process.

2. Citric Acid Cycle (Krebs Cycle)

   • Takes place in the mitochondrial matrix and processes acetyl-CoA derived from pyruvate.
   • Produces 2 ATP, 6 NADH, and 2 FADH2 per glucose molecule.
   • Releases carbon dioxide as a waste product.

3. Electron Transport Chain

   • Located in the inner mitochondrial membrane, it consists of a series of protein complexes.
   • Transfers electrons from NADH and FADH2 to oxygen, forming water.
   • Creates a proton gradient that drives ATP synthesis.

4. Oxidative Phosphorylation

   • Coupled with the electron transport chain, it uses the proton gradient to produce ATP.
   • Involves the enzyme ATP synthase, which synthesizes ATP from ADP and inorganic phosphate.
   • Requires oxygen as the final electron acceptor.

5. ATP Production

   • Total ATP yield from one glucose molecule can be up to 36-38 ATP, depending on the cell type.
   • Includes ATP from glycolysis, the Krebs cycle, and oxidative phosphorylation.
   • ATP serves as the primary energy currency of the cell.

6. NAD+ and FAD as Electron Carriers

   • NAD+ and FAD are essential coenzymes that transport electrons during cellular respiration.
   • NAD+ is reduced to NADH, while FAD is reduced to FADH2, both carrying high-energy electrons to the electron transport chain.
   • They play a crucial role in energy production and metabolic pathways.

7. Aerobic vs. Anaerobic Respiration

   • Aerobic respiration requires oxygen and produces more ATP (up to 38 ATP).
   • Anaerobic respiration occurs without oxygen, resulting in less ATP (2 ATP) and byproducts like lactic acid or ethanol.
   • The choice between aerobic and anaerobic pathways depends on oxygen availability.

8. Fermentation

   • A type of anaerobic respiration that allows glycolysis to continue by regenerating NAD+.
   • Produces lactic acid in animals or ethanol and carbon dioxide in yeast.
   • Provides a quick energy source but is less efficient than aerobic respiration.

9. Mitochondrial Structure and Function

   • Mitochondria have a double membrane: an outer membrane and a highly folded inner membrane (cristae).
   • The matrix contains enzymes for the Krebs cycle and mitochondrial DNA.
   • Mitochondria are known as the powerhouse of the cell due to their role in ATP production.

10. Substrate-level Phosphorylation

    • A direct method of ATP production that occurs during glycolysis and the Krebs cycle.
    • Involves the transfer of a phosphate group from a substrate molecule to ADP, forming ATP.
    • Does not rely on the electron transport chain or chemiosmosis.

11. Chemiosmosis

    • The process by which ATP is produced using the energy from the proton gradient created by the electron transport chain.
    • Protons flow back into the mitochondrial matrix through ATP synthase, driving ATP synthesis.
    • Essential for efficient ATP production in aerobic respiration.

12. Proton Gradient

    • Established by the electron transport chain as protons are pumped from the mitochondrial matrix to the intermembrane space.
    • Creates a potential energy difference (proton motive force) that drives ATP synthesis.
    • The gradient is crucial for the process of chemiosmosis.

13. ATP Synthase

    • An enzyme located in the inner mitochondrial membrane that synthesizes ATP from ADP and inorganic phosphate.
    • Utilizes the energy from the proton gradient to catalyze ATP production.
    • Functions like a turbine, converting the flow of protons into chemical energy.

14. Regulation of Cellular Respiration

    • Controlled by the availability of substrates, energy needs of the cell, and feedback mechanisms.
    • Key enzymes, such as phosphofructokinase in glycolysis, are regulated by ATP, ADP, and citrate levels.
    • Ensures that energy production matches cellular demand.

15. Energy Yield and Efficiency

    • Theoretical maximum yield from one glucose molecule is 38 ATP, but actual yield is often lower (around 30-32 ATP).
    • Efficiency of cellular respiration is about 40%, with the rest of the energy lost as heat.
    • Factors affecting yield include the type of cell, conditions, and metabolic pathways utilized.