What Is ATP in Biology? Adenosine Triphosphate Facts (2024)

In biology and biochemistry, ATP is the acronym for adenosine triphosphate, which is the organic molecule responsible for intracellular energy transfer in cells. For this reason, it’s often called the “energy currency” of metabolism and cells. Here is a look at ATP structure, its functions, how ATP transfers energy, and interesting facts about the molecule.

Why Is It So Important?

There are basically three reasons why ATP is so important in biology:

1. It’s the molecule the body uses directly as energy.
2. Other forms of chemical energy get turned into ATP.
3. It’s easy to recycle, so a cell can use a single molecule again and again.

Structure of the ATP Molecule

You can think of ATP as a molecule built from three subunits: adenine, ribose, and phosphate groups. The purine base adenine binds to the pentose sugar ribose, forming adenosine. The way this works is the 9′ nitrogen atom from adenine bonds to the 1′ carbon of ribose. The phosphate groups attach sequentially to 5′ carbon of the ribose. So, the 5′ carbon from ribose bonds to the oxygen of the first phosphate group. This opposite oxygen connects to the phosphorus of the next phosphate group, and so on. The phosphate groups are alpha (α), beta (β), and gamma (γ), starting from the group closest to the ribose.

If you remove one phosphate group from ATP, you get ADP (adenosine diphosphate). Removing two phosphate groups from ATP forms AMP (adenosine monophosphate). Adding phosphates is the process of phosphorylation, while removing them is dephosphorylation. Forming ATP from AMP or ADP requires energy, while releasing phosphate groups by forming ADP or AMP from ATP releases energy.

Note that while cells mainly use ATP, ADP, and AMP, a similar process occurs using other nitrogenous bases. For example, phosphorylation of guanosine forms GMP, GDP, and GTP.

ATP Functions

ATP serves many function in cells, including providing energy for active transport, muscle contraction, DNA and RNA synthesis, signaling between synapses, and intracellular signaling.

Here are some metabolic processes that use ATP:

• Cell division
• Aerobic respiration
• Fermentation
• Motility
• Muscle contraction
• Photophosphorylation
• Endocytosis
• Exocytosis
• Protein synthesis
• Photosynthesis
• Neurotransmission
• Intracellular signaling

How ATP Works

ATP is how cells turn the sugar glucose into a useful form of chemical energy. Synthesis of ATP primarily occurs within the mitochondrial matrix using the enzyme ATP synthase in the process of cellular respiration. For each molecule of glucose oxidized in respiration, the mitochondria produces about 32 molecules of ATP. ATP production also occurs under anaerobic conditions, but in humans this process only yields two molecules of ATP per molecule of glucose. Plants generate ATP in mitochondria, plus they also make it in chloroplasts.

To use ATP for energy, the cell cleaves the chemical bond between phosphate groups. This bond, called a phosphodiester bond, holds a lot of energy because there is a significant repulsion between phosphate groups due to their electronegativity. Breaking the phosphodiester bond is an exothermic reaction, so it releases heat. While heat is a form of energy, it not how a cell uses ATP for power. Instead, the energy release from turning ATP into ADP (or AMP) is coupled to an energetically unfavorable (endothermic) reaction, giving it the activation energy it needs to proceed. The final energy carriers are electrical charges in the form of protons (H⁺ ions), electrons, or other ions.

Interesting ATP Facts

Here are some interesting facts about ATP or adenosine triphosphate:

• The amount of ATP recycled each day is about the same as your body weight, even though the average person only has about 250 grams of ATP at any given time. In other words, a single ATP molecule gets recycled 500 to 700 times per day.
• At any given moment, your body has about the same amount of ADP (adenosine diphosphate) as ATP. This is important because cells can’t store ATP, so having ADP present as a precursor allows for quick recycling.
• Karl Lohmann and Cyrus Fiske/Yellapragada Subbarow independently discovered ATP in 1929.
• Fritz Albert Lipmann and Herman Kalckar discovered they key tole ATP plays in metabolism in 1941.
• Alexander Todd first synthesized ATP in 1948.
• The 1997 Nobel Prize in Chemistry honored Paul D. Boyer and John E. Walker for clarifying the enzymatic mechanism of ATP synthesis and to Jens C. Skou for discovering the ion-transporting enzyme Na⁺, K⁺-ATPase.

References

• Berg, J. M.; Tymoczko, J. L.; Stryer, L. (2003). Biochemistry. New York, NY: W. H. Freeman. ISBN 978-0-7167-4684-3.
• Ferguson, S. J.; Nicholls, David; Ferguson, Stuart (2002). Bioenergetics 3 (3rd ed.). San Diego, CA: Academic. ISBN 978-0-12-518121-1.
• Knowles, J. R. (1980). “Enzyme-catalyzed phosphoryl transfer reactions”. Ann. Rev. Biochem. 49: 877–919. doi:10.1146/annurev.bi.49.070180.004305
• The Nobel Prize in Chemistry (1997). Nobelprize.org
• Törnroth-Horsefield, S.; Neutze, R. (December 2008). “Opening and closing the metabolite gate”. Proc. Natl. Acad. Sci. USA. 105 (50): 19565–19566. doi:10.1073/pnas.0810654106

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