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Biology LibreTexts

17.4: Adenosine Triphosphate (ATP)

Skills to Develop

  1. State what the letters ADP and ATP stand for and how the two molecules differ.
  2. Briefly describe how energy that is released from energy-containing compounds is trapped and stored as ATP and how energy stored in ATP is released to do cellular work.

Adenosine triphosphate (ATP) links most cellular exergonic and endergonic chemical reactions. To obtain energy to do cellular work, organisms take energy-rich compounds such as glucose into the cell and enzymatically break them down to release their potential energy. Therefore, the organism needs a way to trap some of that released energy and store the energy in a form that can be utilized by the cell to do cellular work. Principally, energy is trapped and stored in the form of adenosine triphosphate or ATP.

A tremendous amount of ATP is needed for normal cellular growth. For example,a human at rest uses about 45 kilograms (about 99 pounds) of ATP each day but at any one time has a surplus of less than one gram. It is estimated that each cell will generate and consume approximately 10,000,000 molecules of ATP per second. As can be seen, ATP production is an ongoing cellular process.

To trap energy released from exergonic catabolic chemical reactions, the cell uses some of that released energy to attach an inorganic phosphate group on to adenosine diphosphate (ADP) to make adenosine triphosphate (ATP). Because the phosphate groups are all negatively charged, they repel each other and stress the bond holding them together, much like a bent diving board. Thus, energy is trapped and stored in these stressed bonds known as high-energy phosphate bonds. To obtain energy to do cellular work during endergonic anabolic chemical reactions, the organism enzymatically removes the third phosphate from ATP thus releasing the stored energy and forming ADP and inorganic phosphate once again (see Fig. 1).

 

Depending on the type of organism, cells transfer energy and generate ATP by photophosphorylation, by substrate-level phosphorylation, and/or by oxidative phosphorylation. (Phosphorylation refers to the attachment of a phosphate group to a molecule.)

Summary

  1. Cellular energy is primarily trapped and stored in the form of adenosine triphosphate or ATP.
  2. A tremendous amount of ATP is needed for normal cellular growth.
  3. To trap energy released from exergonic catabolic chemical reactions, the cell uses some of that released energy to attach an inorganic phosphate group on to adenosine diphosphate (ADP) to make adenosine triphosphate (ATP). The energy is stored in these high-energy phosphate bonds.
  4. To obtain energy to do cellular work during endergonic anabolic chemical reactions, the organism enzymatically removes the third phosphate from ATP thus releasing the stored energy and forming ADP and inorganic phosphate once again.
  5. Depending on the type of organism, cells transfer energy and generate ATP by photophosphorylation, by substrate-level phosphorylation, and/or by oxidative phosphorylation.

Questions

Study the material in this section and then write out the answers to these question. Do not just click on the answers and write them out. This will not test your understanding of this tutorial.

  1. The acronym ATP stands for________________. (ans)
  2. Describe how cells trap energy released from exergonic catabolic chemical reactions and store it as ATP. (ans)
  3. Describe how cells obtain energy to do cellular work during endergonic anabolic chemical reactions. (ans)
  4. The hydrolysis of ATP is:
    1. an exergonic reaction (ans)
    2. an endergonic reaction (ans)

Contributors

  • Dr. Gary Kaiser (COMMUNITY COLLEGE OF BALTIMORE COUNTY, CATONSVILLE CAMPUS)