Question

Which of the following is absent from host cell mRNA exported into the cytoplasm from the nucleus?

		introns
		5′ 7-methylguanylate cap
		codons
		3′ poly(A) tail

Answer 1

Introns

DNA is transcribed to form mRNA in nucleus. It is premature mRNA and contains introns. Post transcriptional modifications take place in mRNA in nucleus before it is exported to cytoplasm. It has 3 steps -

1. Capping, addition of methylguanosine cap at 5' end.

2. Tailing, addition of poly A residues at 3' end.

3. Splicing, removal of introns and joining of exons.

After these 3 steps, premature mRNA is converted to mature mRNA which is then transported into cytoplasm and is ready to undergo translation to form proteins.

Please rate.

Answer 2

Explanation:

• Host cell mRNA is processed in the nucleus before being exported to the cytoplasm for translation. Here’s what’s kept and what’s removed:

• 5' cap (7-methylguanylate) and 3' poly(A) tail: These are added to protect the mRNA and help it get translated.

• Codons: These are the coding sequences that actually instruct protein synthesis.

•  Introns: These are non-coding regions spliced out (removed) during mRNA processing. They never make it to the cytoplasm—only the mature mRNA (with exons) does.

• 
  

Why not the others?

• The 5' cap and poly(A) tail are essential for stability and translation.

• Codons are the whole point of mRNA—they’re the instructions for building proteins!

• 
  

Simple analogy:

Think of mRNA like a movie. Before export:

• Introns = deleted scenes (cut out).

• Exons (codons) = the final film.

• 5' cap and poly(A) tail = the opening/closing credits (necessary for the movie to play properly).

So, introns are the only thing absent in cytoplasmic mRNA

The correct answer is introns.