ribonucleic acid: any of a class of single-
stranded molecules transcribed from DNA
in the cell nucleus or in the mitochondrion
or chloroplast, containing along the strand
a linear sequence of nucleotide bases that
is complementary to the DNA strand from
which it is transcribed: the composition of
the RNA molecule is identical with that of
DNA except for the substitution of the
sugar ribose for deoxyribose and the
substitution of the nucleotide base uracil
for thymine.
