Two substances of special biological importance

The exact three-dimensional shape of molecules is a matter of great importance. 

A = adenine C = cytosine and G = guanine. This structure was based on the experimental work of a number of people, including the British physicists Maurice H, Wilkins and Rosalind Franklin. 

Of particular importance in biology are adenosine triphosphate (ATP) and nicotinamide adenine dinucleotide (NAD ). The structure of ATP is 

On hydrolysis, particularly under the action of the enzyme adenosine triphosphatase (ATPase), ATP is converted into adenosine diphosphate (ADP) and phosphate. This process is of great importance in metabolism (see p, 246). Under ordinary physiological conditions ATP bears four negative charges, as shown above. 

The importance of this substance is that under the action of an appropriate enzyme it can undergo reduction. If we write NAD simply as 

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