Adenosine Tri-phosphate (ATP)

As over dramatic as it may sound, it is very difficult to over state the importance of this molecule in biology. It is used almost everywhere, for example:

1. It can form one of the 4 bases in DNA.
   • The two membered rings of adenine and guanine are PURINES
     The single membered rings of uracil (from RNA), thymine and cytosine are PYRAMIDINES.
2. It is used in a host of signalling mechanisms
   • The gamma (i.e. the third) phosphate is often attached to protein in order to facilitate a conformational change, which alters the activational state.
3. It provides the necessary energy for a range of enzymatic reactions which would otherwise be energetically unfavourable.
   • The hydrolysis of the gamma phosphate provides about 7.3 kcal/mol of free energy. This is in comparison to the 2 kcal/mol which is released by breaking the link between the alpha phosphate and the ribose. The reason for this diffrence is that the 3 negative charges strong repel each other so that breaking this bond is very favourable.

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• Historical view of muscle contraction.