STRUCTURE OF DNA: Summary Below is a student's summary of the structure of DNA It has some mistakes - And and highlight them then rewrite their answer below with corrections. DNA is composed of three strands that form a triple spiral. Each strand is composed of nucleotides, which each contain a phosphate group, ribose sugar and a nitrogenous base. The four nitrogenous bases found in DNA are adenine, gymine, thymine and cytosine. They form complementary base pairs with oxygen bonds holding them together. Diester bonds hold the nucleotides together in one long chain.