Both DNA and RNA consists of polymers of nucleotides. RNA is single stranded but DNA is double stranded. DNA polynucleotide contains thymine but RNA polynucleotide contains uracil.

Dear student,

DNA molecule is double stranded while RNA is single stranded, if RNA molecule was also double stranded it would eventually resist from being translated into proteins.
DNA contains thymine which makes it energetically more costly, while RNA contains uracil in place of thymine. The only difference between thymine and uracil is the presence of methyl group in thymine, absent in uracil. If uracil was also present in DNA, it would cause difficulties in its transcription.

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