B6 Alexandrite: ATP-ADP Process Notes

Definition of Terms

  • ATP: (Adenosine Triphosphate) Main energy carrier; stores energy for cellular processes. Composed of Adenine, Ribose, and three phosphate groups.

  • ADP: (Adenosine Diphosphate) Lower-energy molecule formed when ATP loses a phosphate group—composed of Adenine, Ribose, and two phosphate groups.

  • Phosphate Group: A phosphorus atom bound to four oxygen atoms, often found in energy-carrying molecules like ATP and ADP, plays a crucial role in transferring energy within cells.

  • Exergonic Reaction: Releases energy (catabolic → A breakdown process that releases energy).

  • Endergonic Reaction: Requires energy (anabolic → A building process that requires energy).

Fueling the Cycle

  • Energy Sources: Glucose (cellular respiration) and sunlight (photosynthesis).

  • ADP: Starting point for ATP synthesis. (Uncharged form)

  • Inorganic Phosphate (Pᵢ): Joins ADP to make ATP.

ATP-ADP Process

  • ATP breaks down, releasing energy for cell functions (exergonic).

  • Results: ADP, free phosphate, and energy.

  • Energy from food or sunlight rejoins ADP and phosphate to create ATP (endergonic).

ATP Hydrolysis

  1. ATP binds to ATPase.

  2. The water molecule breaks the phosphate bond.

  3. Inorganic phosphate and energy are released.

  4. Released Pi phosphorylates another molecule (driving endergonic reactions) or is released.

  5. Released energy powers cellular work via protein changes and direct phosphorylation.

  6. ADP and Pi are released.

ATP Hydrolysis Products

  • ADP

  • Pi (inorganic phosphate)

  • Energy

Cellular Work Powered by ATP Hydrolysis

  • Muscle contractions, active transport, nerve impulse transmission, protein synthesis, etc.

ADP-ATP Process

  • Energy from food rejoins ADP and phosphate to create ATP (endergonic).

  • ATP releases energy when needed (exergonic).

Building ATP

  1. Cells need ATP.

  2. Catabolic processes release energy.

  3. Chemiosmosis creates a proton gradient.

  4. ATP Synthase uses the gradient energy to rotate.

  5. Phosphorylation: Phosphate attaches to ADP, making ATP.

  6. ATP is released to power cellular work.

ATP Synthesis Product

  • ATP

Overall Summary

  • ATP broken down into ADP + Pᵢ releases energy (exergonic).

  • Energy from food or sunlight recharges ADP to form ATP (endergonic).

  • Cycles power cell functions.

Why It Matters

  • Essential for efficient energy storage and use in cells.