Question

Methyl guanosine triphosphate is added at the 5’ end of hn RNA in the process of:
A. Tailing
B. Splicing
C. Capping
D. None of these

Answer 1

Hint: The term hnRNA pertains to the unprocessed mRNA (pre-mRNA) molecules found in the nucleus. The heterogeneous nuclear ribonucleoprotein is made up of hnRNA that is associated with proteins (hnRNP). Methyl guanosine triphosphate is added to the 5' end of the hn-RNA during the post-transcriptional process.

Complete Step by Step Answer:
In eukaryotes, the primary transcript is much larger than that of the mature mRNA and is known as Heterogeneous nuclear RNA (hnRNA). It includes unique sequences and approximately ten times the number of sequences as mature mRNA. Since hnRNA is processed before producing mRNA, it is referred to as "mRNA precursor" or "pre-mRNA".
Poly (A) tail is added at the 3′ ends after transcription, and the polymerization reaction is catalyzed by the enzyme "poly (A) polymerase." This enzyme, which does not need a DNA template, adds approximately 200 adenine nucleotides to the 3′ OH- end of hnRNA.
hnRNA is made up of coding sequences (exons) and noncoding sequences known as "intervening sequences" (introns). These sequences are found alternating with one another, known as split genes. During the processing, introns are disintegrated and exons are joined in the correct sequence; this is known as RNA splicing. Several ribonucleoprotein particles known as "snRNPs" are involved in intron removal and RNA splicing.
A "cap" is constituted at the 5′ ends of RNA during processing. The cap comprises one or two nucleotides with methylated sugars at the 2′ positions. A triphosphate bridge connects the methylated nucleotide to 7-methylguanosine. At the 5′-end of mRNA, 7-methylguanosine binds to 5′-triphosphate and thus stops at the 3′-OH end. So, capping is the process in which methyl guanosine triphosphate is added at the 5’ end of hn RNA.
The correct option is C.



Note: Capping may also influence transcript stability, describing variance in half-lives between prokaryotic and eukaryotic mRNAs. Furthermore, the fact that cap analogs can hinder splicing when added early in the reaction but not afterward indicates that cap acknowledgment is an essential step in the creation of a specific ribonucleoprotein complex needed for splicing.