DNA stands for Deoxyribose [blank_start]Nucleic[blank_end] Acid. A monomer unit of DNA is a [blank_start]nucleotide[blank_end]. Each nucleotide has [blank_start]3[blank_end] (<< type the number please) parts: a phosphate group, a deoxyribose [blank_start]sugar[blank_end], and a nitrogen [blank_start]base[blank_end]. There are [blank_start]4[blank_end] (<< type the number please) types of nitrogen bases: adenine, guanine, [blank_start]thymine[blank_end], and cytosine. Adenine and guanine are larger and therefore are [blank_start]purines[blank_end]. Thymine and cytosine are [blank_start]pyrimidines[blank_end].