ATP is a universal form of free energy in all living organisms and is an energy coupling agent (Tymoczko et al. 2013. p. 250). When ATP is hydrolyzed to produce adenosine diphosphate (ADP) and orthophosphate (Pi), or to adenosine monophosphate (AMP) and Pi, free energy is released. This free energy can then be used for endergonic reactions that require a free energy input to occur. ATP/ADP recycling is critical for energy exchange in living organisms. ATP is critical in photosynthesis as it is used to produce carbohydrates from carbon dioxide (Tymoczko et al. 2013. p. 407). Thermodynamically unfavorable reactions can also occur if they are coupled to ATP hydrolysis in a new reaction (Tymoczko et al. 2013. p. 250). The structure of adenosine triphosphate (ATP) is composed of a ribose sugar molecule attached to the nucleotide base adenine on one side and attached to three phosphate groups (in a triphosphate unit) on the other side of the ribose sugar (adenosine triphosphate-ATP ). The ATP molecule contains two phosphoanhydride bonds that join the three phosphate groups together and a phosphoester bond that connects one of the phosphate groups to the ribose molecule (Properties of ATP). The two phosphoanhydride bonds are formed through the loss of a water molecule (Tymoczko et al. 2013. p. 250). ATP is formed in chemotrophs through the oxidation of carbon fuels and in photosynthetic organisms when light energy is converted to chemical energy (Topic 4.2-The Structure and Role of ATP). ATP has a high phosphoryl transfer potential due to its structural differences compared to ADP and Pi. These structural differences include (1) electrostatic repulsion, (2) resonance stabilization, and (3) stabilization du… middle of paper… ibulose 1,5-bisphosphate (Tymoczko et al. 2013. p.412). 12 NADPH are also used in the reduction of the 12 1,3-phosphoglycerate molecules produced during the 6 cycles. Therefore, ATP has a fundamental role in the functioning of the Calvin cycle and photosynthesis since without it, plants would not be able to complete the Calvin cycle and synthesize hexose carbohydrate sugars (Tymoczko et al. 2013. p. 412) Works cited May, P . Adenosine triphosphate-ATP. University of Bristol. Retrieved from http://www.chm.bris.ac.uk/motm/atp/atp1.htmProperties by ATP. UC Davis. Retrieved from http://biowiki.ucdavis.edu/Biochemistry/Oxidation_and_Phosphorylation/ATP_and_Oxidative_Phosphorylation/Properties_of_ATPTopic 4.2-The Structure and Role of ATPTymoczko, J.L., Berg, J.M., and Stryer, L. (2013). Biochemistry: A Short Course, 2nd Edition. New York, NY: W. H. Freeman and Co.