<P> A phosphodiester bond occurs when exactly two of the hydroxyl groups in phosphoric acid react with hydroxyl groups on other molecules to form two ester bonds . </P> <P> Phosphodiester bonds are central to all life on Earth, as they make up the backbone of the strands of nucleic acid . In DNA and RNA, the phosphodiester bond is the linkage between the 3' carbon atom of one sugar molecule and the 5' carbon atom of another, deoxyribose in DNA and ribose in RNA . Strong covalent bonds form between the phosphate group and two 5 - carbon ring carbohydrates (pentoses) over two ester bonds . </P> <P> The phosphate groups in the phosphodiester bond are negatively charged . Because the phosphate groups have a pK near 0, they are negatively charged at pH 7 . This repulsion forces the phosphates to take opposite sides of the DNA strands and is neutralized by proteins (histones), metal ions such as magnesium, and polyamines . </P>

Where are the phosphodiester bonds located in the double helix of dna