1) DNA is a double-helical macro molecule found in the nucleus of eukaryotic cells that is essential for carrying genetic information. 2) DNA is composed of nucleotides, which each contain a nitrogenous base, a 5-carbon sugar (deoxyribose), and a phosphate group. The four nucleotides are deoxyadenosine, deoxyguanosine, deoxycytosine, and deoxythymidine. 3) The two strands of DNA are held together by hydrogen bonds between complementary nucleotide base pairs - adenine pairs with thymine, and cytosine pairs with guanine.