Before leaving the nucleus, the pre-mRNA transcript formed through transcription undergoes a series of enzyme-regulated modifications. Part of the process is illustrated below. Without this modification, why would mRNA be translated into a nonfunctional protein?

Post transcription

Explanation:

Before leaving the nucleus, the pre-mRNA transcript formed through transcription undergoes a series of enzyme-regulated modifications which includes: 5'capping,splicing,3' cleavage(polyadenylation) and RNA editing

5' capping 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-mRNASplicing is the second modification event of pre-mRNA occurs in nucleus just after transcription but before the RNA moves to the cytoplasmIn RNA splicing non coding regions of pre-mRNA called introns are removed and coding regions called exons are religated If this modification does not occur then introns will be copied from DNA that will interrupt the genetic codeMost of mature eukaryotic mRNA have 50-250 adenine residue at the 3'end called Poly A tailThese nucleotides are not encoded by the genome but are added after transcription,process is called is both template and primer independent process catalysed by polyadenylate polymerase and protects mRNA from exonuclease at 3'end RNA editing is defined as the change of nucleotide sequence of RNA which is carried out in two different ways: site specific base modification and insertional or deletion type of RNA editing

Introns are regions of pre-mRNA copied from DNA that interrupt the genetic code.

Explanation:

1. DNA is first transcribed into pre-mRNA, then this pre-mRNA further go series of modification, like 5' capping, 3' polyadenylation and RNA splicing.

2. Through splicing, introns are removed and exons are joined together to form a mature RNA known as mRNA.

3. If without these modifications, RNA is translated, it would encode non-functional protein because all the codons in the pre-mRNA would translated and introns would code a non-functional protein.

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