In terms of structure : A purine is a heterocyclic aromatic compound that consists of a pyrimidine ring fused to a imidazole ring.It consists of 2 carbon- nitrogen rings together with four nitrogen atoms whereas pyrimidine is a heterocyclic aromatic compound consisting of nitrogen atoms that are present on 1st and 3rd position of the ring.So,pyrimidine contains 1 carbon- nitrogen ring and two nitrogen atoms. In terms of molecular weight: Molecular weight of purine is 120.11 g/mol whereas molecular weight of pyrimidine is 80.088 g/mol. The pneumonic device that can be used to memorise which bases are purines vs pyrimidines are : for purine nucleotides : It can be remembered as Pure as gold or pure as AG.So,purines are Adenine and guanine. for pyrimidines:It can be remembered as cut the Py because it sound like pie. Also, pie has one ring and so does pyrimidine.So, pyrimidines are cytosine, uracil and thymine. Solution In terms of structure : A purine is a heterocyclic aromatic compound that consists of a pyrimidine ring fused to a imidazole ring.It consists of 2 carbon- nitrogen rings together with four nitrogen atoms whereas pyrimidine is a heterocyclic aromatic compound consisting of nitrogen atoms that are present on 1st and 3rd position of the ring.So,pyrimidine contains 1 carbon- nitrogen ring and two nitrogen atoms. In terms of molecular weight: Molecular weight of purine is 120.11 g/mol whereas molecular weight of pyrimidine is 80.088 g/mol. The pneumonic device that can be used to memorise which bases are purines vs pyrimidines are : for purine nucleotides : It can be remembered as Pure as gold or pure as AG.So,purines are Adenine and guanine. for pyrimidines:It can be remembered as cut the Py because it sound like pie. Also, pie has one ring and so does pyrimidine.So, pyrimidines are cytosine, uracil and thymine..