Which of the following could not be an rna transcript?
answer ggcuag
ccgatc
uuaacc
acggau
gagcau

The answer is the second option namely CCGATC. This is because of the inclusion of T for thymine. RNA never has thymine in its structure but thymine is always replaced with uracil. In RNA, thymine is replaced by uracil as the base complementary to adenine. Uracil is very similar to thymine and is energetically less expensive to produce than thymine which may account for its use in RNA. In DNA however, uracil is readily produced by chemical degradation of cytosine so having thymine which is more stable than uracil in that respect makes it more ideal to have in the DNA structure because it has a higher fidelity than uracil.