Utilization of Energy Stored in Nucleotides

The reaction types outlined above indicate the various ways in which the free energy of ATP can be released through hydrolysis of one or more of its phosphoanhydride bonds. This energy can be used in several different ways to drive endergonic reactions. 

ATP is the primary source of utilizable energy for biosynthetic reactions, but other purine and pyrimidine nucleoside triphosphates (GTP, UTP, CTP) occur in cells and are formed by phosphoryl transfer from ATP, as described in detail in Chapter 4. These are also high-energy compounds, and their hydrolysis can be coupled to energetically unfavorable reactions. This most commonly takes place through nucleotidyl transfer reactions leading to group-transfer coenzymes (Section II, B, 3). 

In those cases in which the products of phosphoryl transfer reactions 

A large group of biosynthetic enzyme reactions, now called ligases, use ATP as an immediate substrate, but no part of the ATP appears attached to any of the products. In terms of the way in which ATP is used, these reactions may be divided into two subclasses. 

In this type of reaction an intermediate enzyme-bound acetyl (acyl) adenylate is believed to be formed this subsequently reacts with some acceptor of the acetyl group, such as Co A  

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