Re: Structure of phosphate group in DNA?

During the process of DNA synthesis, nucleotides are in the
"tri-phosphate" form. That is, each nucleotide has 3 phosphate groups.
However, as DNA polymerase adds on each nucleotide to the growing DNA
chain, it has to find energy to do this, and it acquires energy by
cleaving off two of the phosphate groups. This reaction provides the
energy required to drive DNA synthesis. As a result, the
sugar-phosphate backbone of DNA only has 1 phosphate for each
nucleotide ("mono-phosphate" form).

This is also the reason that the very extreme 5' end of a DNA strand
has 3 phosphate groups on it.

--Alex

*************
Alex B. Berezow, Grad Student
Dept. of Microbiology
University of Washington School of Medicine
Seattle, WA 98195

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