Adenosine Triphosphate Structure

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ATP is 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 liberated. This free energy can then be utilized for endergonic reactions that need an input of free energy in order to occur. The recycling of ATP/ADP is critical to for energy exchange in living organisms. Thermodynamically unfavorable reactions can be driven if they are coupled to ATP hydrolysis in a new reaction.

The structure of adenosine triphosphate (ATP) is composed of a three phosphate groups (in a triphosphate unit) attached to the nucleotide adenine with two phosphoanhydride bonds. The two phosphoanhydride bonds are formed by 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 into 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 structure differences include (1) electrostatic repulsion, (2) resonance stabilization, and (3) stabilization due to hydration (Tymoczko et al. 2013. p. 252) At a neutral pH, ATP has four negative charges that repel each other. However, hydrolysis of ATP reduces this electrostatic repulsion. Also, ADP and Pi have
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