Question: why is the sequence of nitrogen bases in dna important

title: Nitrogenous base
text: In the biological sciences , nitrogenous bases are increasingly termed nucleobases because of their role in nucleic acids - their flat shape is particularly important when considering their roles as the building blocks of DNA and RNA . A set of five nitrogenous bases is used in the construction of nucleotides , which in turn build up nucleic acids like DNA and RNA . These nitrogenous bases are adenine ( A ) , uracil ( U ) , guanine ( G ) , thymine ( T ) , and cytosine ( C ) . The nitrogenous bases form hydrogen bonds between opposing DNA strands to form the rungs of the `` twisted ladder '' or double helix of DNA or a biological catalyst that is found in the nucleotides . Adenine is always paired with thymine , and guanine is always paired with cytosine . These are known as base pairs . Uracil is only present in RNA , replacing thymine . Pyrimidines include thymine , cytosine , and uracil . They have a single ring structure . Purines include adenine and guanine . They have a double ring structure .