Water reaction with adenosine triphosphate

The relative strengths of bonds are important for understanding the way that energy is used in bodies to power our brains and muscles. For instance, adenosine triphosphate, ATP (35), is found in ever)- living cell. The triphosphate part of this molecule is a chain of three phosphate groups. One of the phosphate groups is removed in a reaction with water. The P O bond in ATP requires only 276 kjmol-1 to break and the new P—O bond formed in H2P04 releases 350 kj-mol-1 when it forms. As a result, the conversion of ATP to adenosine diphosphate, ADP, in the reaction... 

The oxygen formed clearly comes from H20 and not from C02, because photosynthesis in the presence of water labeled with lgO produces oxygen labeled with 180, whereas carbon dioxide labeled with 180 does not give oxygen labeled with 180. Notice that the oxidation of the water produces two electrons, and that the formation of NADPH from NADP requires two electrons. These reactions occur at different locations within the chloroplasts and in the process of transferring electrons from the water oxidation site to the NADP reduction site, adenosine diphosphate (ADP) is converted to adenosine triphosphate (ATP see Section 15-5F for discussion of the importance of such phosphorylations). Thus electron transport between the two photoprocesses is coupled to phosphorylation. This process is called photophosphorylation (Figure 20-7). 

To 17 parts by volume of the crude enzyme solution are added 5 parts of kanamycin B, 50 parts by volume of 0.5 M phosphate buffer (pH 7.0), 100 parts by volume of 1 M adenosine triphosphate solution, 50 parts by volume of 0.1 M magnesium acetate solution and 50 parts by volume of 0.1 M 2-mercaptoethanol, which is filled up to 500 parts by volume with distilled water. The mixture is subjected to enzymic reaction at 37°C for 20 h. 

Substitution and elimination reactions are so useful that it is not surprising that they occur in nature. Alkyl halides, however, are not compatible with cytoplasm because they are hydrocarbon-like and therefore insoluble in water. In the cell, alkyl phosphates play the role that alkyl halides do In the laboratory. Adenosine triphosphate (ATP) is an example of a biologically important alkyl phosphate. We will abbreviate its structure here as follows (the full structure is given in Sec. 1 8.12). 

Stage 2— Carbon dioxide (CO,) combines with the released hydrogen to form the simple sugars and water. This reaction is energized (powered) by ATP (adenosine triphosphate), a stored source of energy. Neither chlorophyll nor light is involved in this stage. 

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