036 CHAPTER 27 Nucleosides, Nucleotides, and Nucleic Acids
Because phosphoric acid can form an anhydride, nucleotides can exist as monophos-
phates, diphosphates, and triphosphates. They are named by adding monophosphateor
diphosphateor triphosphateto the name of the nucleoside.PROBLEM 2Draw the structure for each of the following:a. dCDP c. dUMP e. guanosine
b. dTTP d. UDP f. adenosine27.2 ATP: The Carrier of Chemical Energy
All cells require energy to ensure their survival and reproduction. They get the
energy they need by converting nutrients into a chemically useful form of energy.
The most important form of chemical energy is adenosine -triphosphate (ATP).
The importance of ATP to biological reactions is shown by its turnover rate in hu-
mans—each day, a person uses an amount of ATP equivalent to his or her body
weight. ATP is known as the universal carrier of chemical energy because, as it is
commonly stated,“the energy of hydrolysis of ATP converts endergonic reactions
into exergonic reactions.”
In other words, the ability of ATP to enable otherwise unfavorable reactions to
occur is attributed to the large amount of energy released when ATP is hydrolyzed,
which can be used to drive an endergonic reaction. For example, the reaction of5 ¿3 ¿-monophosphate5 ¿-triphosphatephosphoric acid pyrophosphoric acid triphosphoric acidOOHP
+∆
5 HO OH P 2 O 5 OOOHP
OHOOHP
HO OOOHP
OOOHP
OHOOHP
HONNNN−O OOPO−NH 2OHO OH
adenosine
5 ′-monophosphate
AMPNNNNO OOPO−−OOPO−NH 2OHO OH
adenosine
5 ′-diphosphate
ADPNNNNO OOPO−−OOPO−OOPO−NH 2OHO OH
adenosine
5 ′-triphosphate
ATPNNNN−O OOPO−NH 2OHO
2 ′-deoxyadenosine
5 ′-monophosphate
dAMPNNNNO OOPO−−OOPO−NH 2OHO
2 ′-deoxyadenosine
5 ′-diphosphate
dADPNNNNO OOPO−−OOPO−OOPO−NH 2OHO
2 ′-deoxyadenosine
5 ′-triphosphate
dATP