Question

In order to test the effects of a new drug, you isolate the messenger RNA molecules from both treated and untreated eukaryotic cells and separate them according to size using gel electrophoresis. The samples that were loaded into each of the four lanes are as follows:
Lane 1: the primary RNA transcripts isolated from the nucleus of untreated cells Lane
2: the primary RNA transcripts isolated from the nucleus of cells treated with the drug being tested Lane
3: RNA isolated from the cytosol of untreated cells Lane
4: RNA isolated from the cytosol of cells treated with the drug being tested

Which of the following conclusions is most likely to be CORRECT?

A. These results suggest that the drug affects RNA processing.B. These results suggest that the drug digests DNA.C. These results suggest that the drug inhibits DNA replication.D. These results suggest that the drug contains a protease that targets this gene product.E. These results suggest that the drug inhibits post-translational processing of this gene.

Answer 1

A) option is correct

Explanation:

RNA processing involves 5'capping,splicing,polyadenylation and RNA editing

1) 5'capping

• It is the first modification event in the pre mRNA that occurs after 20-30 nucleotide addition
• In capping a 7 methyl guanosine(cap) is added to the 5' end of pre mRNA
• Capping protects 5'end of pre mRNA from degradation by exoribonucleases and facilitate transportation form nucleus to cytoplasm

2) Splicing

• Splicing is the second modification event of pre mRNA and occurs in nucleus just after transcription but before the RNA moves to the cytoplasm
• In RNA splicing non coding regions of pre mRNA called introns are removed and coding regions called exons are religated

3) Polyadenylation

• Most of mature RNA have 50-250 adenine residues at the 3'end called Poly A tail
• These nucleotides are not encoded by the genome but are added after transcription,process is called polyadenylation
• Polyadenylation is both template and primer independent process catalysed by polyadenylate polymerase(PAP)
• PAP uses ATP as a precursor and adds the nucleotides using same chemistry as RNA Polymerase
• Poly A tail protects mRNA from exonucleases at 3' end

4) RNA editing

• RNA editing is defined as changing of nucleotide sequence of RNA resulting mature RNA differs from which encoded by genomic sequence
• RNA editing is carried out in two different ways:
• Site specific base modification RNA editing is the one in which deamination of cytosine and adenine are common types of modification
• Insertional or Deletion type of RNA editing is the one which is more common where uridine is inserted or deleted from specific region after transcription