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-mRNA
• Splicing is the second modification event of pre-mRNA 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
• If this modification does not occur then introns will be copied from DNA that will interrupt the genetic code
• Most of mature eukaryotic mRNA have 50-250 adenine residue 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 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

Answer:

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.