Question

5- PolyT oligomers bound to a matrix resin column will selectively isolate which of the following? a. Ribosomal RNA b. GC-rich DNA c. Transfer RNA d. Messenger RNA

Answer 1

Ans:-) option d. Messenger RNA.

Oligomer is molecular complex of chemicals that consist of many repeating units.

Now come to the question :-

Cell extract - - - - - - - - - > DNA+RNA+Proteins

We know RNA is of 3 types.

i) mRNA ii) tRNA iii) rRNA

Among these rRNA is most abundant and after that mRNA.

In eukaryotes, some post transcriptional or during transcription some modifications occur in mRNA.

At 5' end cap is attached and at 3' end polyadenylation occurs. Polyadenylation is covalent linkange of polyadenylyl moiety at 3' end. In eukaryotes, with the exception of histones, all the messenger RNA molecules are polyadenylated at 3' end. The poly (A) tail and protein bound to it aid in protecting mRNA from degradation by exonuclease. Polyadenylation is also important for transcription termination,export of mRNA from nucleus and translation.

Polyadenylation occurs during and immediately after transcription of DNA into RNA. After transcription has been terminated, the mRNA chain is cleaved through action of endonuclease complex associated with RNA polymerase. After the mRNA has been cleaved, around 250 adenosine residues are added to free 3' end at cleavage site. This reaction is catalysed by polyadenlate polymerase.

Now here we have to purify mRNA using oligo dT column.

Take a column and this column is having many beads made up of solid matrix and matrix we may called as synthetic tail made up of synthetic thymine. This is also called as oligo dT column. Now put the DNA - RNA solution or simply RNA extract into the column. Among these since mRNA is having many adenyl residues at its 3' end and we know that adenine form hydrogen bonds with thymine. So the mRNA will bind to the dT chain or we can say with matrix while other kind of RNA like rRNA and tRNA (DNA if taken) will remain suspended. We can extract this mRNA by changing the ionic strength of buffer.

Date Page cell extract - DNA +RNA + Proteins ~ Protein taken out DNA +RNA DNA taken out RNA MRNA rRNA tRNA scap AAAAA Poly (A) tait ather hva molecule NO.0.0 -Bosh hound with olige at Bead / matrix

Hence poly T oligomers bound to a matrix resin column will selectively isolate messenger RNA.

Since tRNA, rRNA and GC rich DNA donot have much adenine to bind with thymine. So they are not isolated.