Answer:
In the ATP-ADP cycle, energy is released or stored as chemical bonds are broken or formed between phosphate groups. Here's how the cycle works:
Explanation: 1. ATP (Adenosine Triphosphate): ATP is the primary energy currency of cells. It consists of an adenosine molecule (adenine base and ribose sugar) linked to three phosphate groups.
2. Energy Release: When a cell needs energy, ATP is hydrolyzed, meaning it loses one of its phosphate groups, becoming ADP (Adenosine Diphosphate), and releases energy. This reaction can be represented as follows:
ATP → ADP + Pi + Energy
In this reaction, Pi represents an inorganic phosphate group.
3. Energy Storage: Conversely, when a cell needs to store energy, ADP can undergo phosphorylation, where it gains a phosphate group, converting back into ATP. This process occurs during cellular respiration and photosynthesis when energy from food or sunlight is used to add a phosphate group to ADP.
ADP + Pi + Energy → ATP
During this cycle, energy is released when ATP is converted to ADP and inorganic phosphate (Pi), and energy is stored when ADP and Pi are converted back into ATP. This energy transfer is fundamental to various cellular processes, providing the necessary energy for activities such as muscle contraction, active transport, and synthesis of biomolecules.