ATP

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ATP, or Adenosine Triphosphate, is the universal energy currency for all living things. Every cell in the world uses ATP for energy. It consists of a base (adenine) and three phosphate groups. It can be made many different ways, but mainly it is made by cellular respiration.

[edit] How it is formed

ATP is formed in almost the same way in photosynthesising plants and animals. In plants, ATP is made during a stage of photosynthesis. When an excited electron activates a gate that allows protons in the cell, the protons can not get out. As the concentration increases, the internal pressure increases as well. Soon, a small gate opens, allowing protons through. Upon their exit, the proton starts a reaction between an ADP molecule (Adenosine Diphosphate) and a phosphate. The two are joined together and form ATP. However, in animals, ATP is made during Cellular respiration: it makes 2 ATP molecules in glycolysis, and 36 in the electron transport chain. Therefore, cellular respiration creates a total of 38 ATP in one cycle.

[edit] How it is used

ATP is a very versatile molecule, meaning that it can be used for many things. Energy is stored in chemical bonds in molecules. When a bond is broken, energy is released. Also, when a bond is made, energy is stored. When ADP binds with another phosphate, energy is stored that can be used later. When ATP breaks a bond with a phosphate group and becomes ADP, energy is released. The ATP phosphate exchange is a nearly never-ending cycle, stopping only when the cell dies. ATP gives energy to most of the cell's functions: the sodium-potassium pumps in the cell membrane require ATP to break into ADP and the loose phosphate must bind to the pump. All active transports require ATP in some form.