Question

RNA polymerase is incubated with a DNA template, all the necessary transcription factors, and the substrates: ATP, GTP, CTP, and UTP. Each ribonucleotide 5’-triphosphate substrate is labeled with 18O in the β-phosphate group and 13C in the ribose. What labeled RNA is produced?

Group of answer choices:

The newly synthesized RNA will have 13C-ribose at every nucleotide residue, but no 18O-atoms incorporated.

The newly synthesized RNA will have an 18O-atom and a 13C-ribose at every nucleotide residue.

The newly synthesized RNA will have 13C-ribose at every nucleotide residue, but only an 18O-atom at the 5’-end.

The newly synthesized RNA will have 13C-ribose at every nucleotide residue, but only an 18O-atom at the 3’-end.

The newly synthesized RNA will have 13C-ribose at every nucleotide residue, but only an 18O-atom at the 5’-end and the 3’-end.

Answer 1

The newly synthesized RNA will have 13C-ribose at every nucleotide residue, but only an 18O-atom at the 5’-end.

RNA synthesis by RNA Polymerase involves the addition of Nucleotide triphosphste (NTPs) to the 3' - OH group of previously added base. This involves the release of the beta and gamma phosphate groups of the newly added NTP. However the first nucleotide is added denovo and the two phosphates are not released for the first nucleotide. Therefore the heavy isotopes will be found for the first phosphate, but all Sugars will have the heavy Carbon.