The structure of ATP has an ordered carbon compound as a
backbone,
but the part that is really critical is the phosphorous part - the
triphosphate. Three phosphorous groups are connected by oxygens to each
other, and there are also side oxygens connected to the phosphorous
atoms. Under the normal conditions in the body, each of these oxygens
has a negative charge, and as you know, electrons want to be with
protons - the negative charges repel each other. These bunched up
negative charges want to escape - to get away from each other, so there
is a lot of potential energy here.
If you remove just one of these phosphate groups from
the end, so
that there are just two phosphate groups, the molecule is much happier.
This conversion from ATP to ADP
is an extremely crucial reaction for the supplying of energy for life
processes. Just the cutting of one bond with the accompanying
rearrangement is sufficient to liberate about 7.3 kilocalories per mole
= 30.6 kJ/mol. This is about the same as the energy in a single peanut.
Living things can use ATP like a battery. The ATP can
power needed
reactions by losing one of its phosphorous groups to form ADP, but you
can use food energy in the mitochondria to convert the ADP back to ATP
so that the energy is again available to do needed work. In plants,
sunlight energy can be used to convert the less active compound back to
the highly energetic form. For animals, you use the energy from your
high energy storage molecules to do what you need to do to keep
yourself alive, and then you "recharge" them to put them back in the
high energy state. The oxidation of glucose operates in a cycle called
the Krebs cycle in animal cells to provide energy for the conversion of
ADP to ATP.
