Nucleic Acid Structure and General Features

ID #2216

Why do purines and pyrimidines have the same amount of usable energy?

The storage of energy in the nucleotides is NOT in the nitrogenous purine or pyrimidine base. Instead the energy is in the repelling force of the negatively charged phosphate groups present in both pyrimidines and purines. That is why breaking a purine like ATP-->ADP + Pi releases energy because you're simply breaking off a phosphate group from two other phosphate groups attached to a ribose sugar and adenine base. A cell typically doesn't use this as an energy source, but you could say the same for breaking down a pyrimidine like CTP. 

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