Question

A eukaryotic cell carrying out transcription and RNA processing is incubated with 32P-labeled ATP. Where will the radioactive isotope appear in mature mRNA if the ATP is labeled at the (a) α position, (b) β position, and (c) γ position?

Short answer

The ATP labelled at alpha position appears in the phosphate groups in the phosphodiester backbone of the m RNA and at all sites 32-P containing ATP is introduced as a substrate by RNA polymerase.

Step-by-step solution

ATP  as an higher nucleotide.

ATP is the higher nucleotide having two high energy phosphate bonds and thus occurs in the m RNA as a structural component of it. The bond energy released by breaking of these phosphate bonds is used up to form the bonds between base pairs during the process of transcription. So radioactive or 32 P radiolabelled ATP will appear in different regions depending on the position at which it is labelled in the DNA during the process of transcription.

Explanation.

The ATP labelled at alpha position appears in the phosphate groups in the phosphodiester backbone of the mRNA and at all sites 32-P containing ATP is introduced as a substrate by RNA polymerase. In the ATP labelled at beta position 32 P appears only at 5’end of m RNA that contains the sequence as A as the first residue. In other cases at $\sigma 70$location, 32 bound ATP used as substrate for RNA synthesis, the phosphates are released out as PPi.

In the ATP labelled at gamma position, 32 P will not appear in the RNA chain. During polymerization, the phosphates are released out as PPi. The terminal position in the gamma residues at the 5’end on the A residue are removed during the capping process of mRNA.