In the DNA's double helix the nucleotides used are adenine (A), timine (T), Guanine (G), cytosine (C) and A will pair with T, while C will pair with G.
Meanwhile, RNA sequences are formed by the following nucleotides: adenine (A), uracil (U), Guanine (G), cytosine (C). In RNA, A pairs with U, while C will pair with G.
So, the DNA codon CGA would be transcribed on mRNA as GCU.
