Page 114 - Demo 1

Figure 51. Structure of ATP
Source: https://ka-perseus-images.s3.amazonaws.com/9b3e651e6dc5d6fb4883e4fb5e5b72c147cbdec0.png

Structurally, ATP is an RNA nucleode that is made up of three
phosphates. At the center of the molecule lies a five-carbon sugar, ribose,
which is aached to the nitrogenous base adenine and to the chain of three
phosphates. The three phosphate groups, in order of proximity to the ribose
sugar, are labeled alpha, beta, and gamma. ATP is made unstable by the three
negavely-charged phosphate groups that repel each other. The bonds between
the phosphate groups are “high-energy” bonds. It takes energy to overcome
the repulsion, as well as link them by chemical bonds.

ATP easily loses the last phosphate group because the breakdown
products, ADP (adenosine diphosphate) and a separate phosphate group, are
more stable than ATP. A significant amount of energy is released when one of
the high-energy bonds is broken in a hydrolysis (water-mediated breakdown)
reacon. ATP is hydrolyzed to ADP in the following reacon:

ATP + H2O ⇋ ADP + Pi + energy

Like most chemical reacons, the hydrolysis of ATP to ADP is reversible.
The reverse reacon, which regenerates ATP from ADP and Pi (inorganic
phosphate), requires energy. The ATP regeneraon reacon is simply the reverse
of the hydrolysis reacon:

energy + ADP + Pi ⇋ ATP + H2O

The energy released by the hydrolysis of ATP is used to power many
energy-requiring cellular reacons. The connuous process of breakdown and
synthesis of ATP is referred to as the ATP-ADP cycle. ATP holds energy for only
a short period of me before it is ulized in an energy-requiring reacon. Then ATP
is synthesized from ADP and Pi. Each ATP molecule undergoes about 10,000
cycles of hydrolysis and regeneraon every day.

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