Describe the structure of ATP and how it stores energy?

Answer 1

Stable chemical bonds release energy as they form, and bond formation thermodynamically happens spontaneously. However, formation reactions often do require energy of activation to rearrange bonds and get reactions over activation barriers (which usually involves breaking bonds first before forming new ones). Stable bond formation is always exoergic.

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.

Why do chemical bonds appear to "store" energy? They certainly "contain" energy, but energy must be added to get any energy out. Where can the energy for breaking bonds come from -- only when stronger bonds are formed instead? This is the true driving energy for biochemistry, where cellular respiration provides energy by forming the strong oxygen bonds in carbon dioxide and water, breaking the weaker bonds in carbohydrates and sugars. In photosynthesis, energy from the sun is used to break the CO2 and H2O bonds (overall), and the fairly strong O2 bond is formed as well. The larger the difference between the bond energies of the formed products (CO2 and H2O) and the reactants, the more energy is available. So, in fact, more energy is "available" when the weakest bonds are broken in favor of the stronger bonds being formed. ATP provides energy when it transfers phosphate groups to more strongly bonded glucose or fructose phosphates.