<P> Nucleotides contain either a purine or a pyrimidine base--i.e., the nitrogenous base molecule, also known as a nucleobase--and are termed ribonucleotides if the sugar is ribose, or deoxyribonucleotides if the sugar is deoxyribose . Individual phosphate molecules repetitively connect the sugar - ring molecules in two adjacent nucleotide monomers, thereby connecting the nucleotide monomers of a nucleic acid end - to - end into a long chain . These chain - joins of sugar and phosphate molecules create a' backbone' strand for a single - or double helix . In any one strand, the chemical orientation (directionality) of the chain - joins runs from the 5' - end to the 3' - end (read: 5 prime - end to 3 prime - end)--referring to the five carbon sites on sugar molecules in adjacent nucleotides . In a double helix, the two strands are oriented in opposite directions, which permits base pairing and complementarity between the base - pairs, all which is essential for replicating or transcribing the encoded information found in DNA . </P> <P> Unlike in nucleic acid nucleotides, singular cyclic nucleotides are formed when the phosphate group is bound twice to the same sugar molecule, i.e., at the corners of the sugar hydroxyl groups . These individual nucleotides function in cell metabolism rather than the nucleic acid structures of long - chain molecules . </P> <P> Nucleic acids then are polymeric macromolecules assembled from nucleotides, the monomer - units of nucleic acids . The purine bases adenine and guanine and pyrimidine base cytosine occur in both DNA and RNA, while the pyrimidine bases thymine (in DNA) and uracil (in RNA) in just one . Adenine forms a base pair with thymine with two hydrogen bonds, while guanine pairs with cytosine with three hydrogen bonds . </P> <P> Nucleotides can be synthesized by a variety of means both in vitro and in vivo . </P>

The genetic code is contained within the nucleotide sequences of what type of organic molecule