Question

hnRNA is a
a. Heterogenous nuclear RNA
b. Homonuclear RNA
c. Heterogeneous RNA
d. Useful RNA

Answer 1

Hint: Mostly it is present outside the nucleolus. It is largely composed of the pre-mRNA molecules that need extensive processing to become mature mRNA molecules.

Complete answer:
The hnRNA is the collective term for the unprocessed mRNA (pre-mRNA) molecules in the nucleus. The hnRNA that is associated with proteins form the heterogeneous nuclear ribonucleoprotein (hnRNP).
The preliminary step of synthesizing mRNA is transcription. During transcription, the DNA sequence is read by RNA polymerase for the second to create a complementary, antiparallel RNA strand (called primary transcript). The primary transcript that afterward becomes a messenger RNA (mRNA) is known as a pre-mRNA. The pre-mRNA sequentially requires undergoing extra processing to become a fully functional mature mRNA.
hnRNA is the shortened form for heterogeneous nuclear ribonucleic acid: an extrachromosomal RNA molecule in the nucleus that provides a primary transcript from DNA.

Hence, Option (A) is the correct answer.

Additional Information:
A pre-mRNA molecule becomes a mature mRNA molecule after undergoing the following processes:
5′ cap addition – the joining of a 5’cap to the front or 5′ end of the pre-mRNA molecule at the start of transcription.
splicing – deletion of any introns (non-coding sequences) and the splicing jointly of exons (protein-coding sequences).
editing – in a few cases, the nucleotide composition is distorted.
polyadenylation – a poly tail is added to the free 3′ end at the cleavage site.

Note: Main features of hnRNA are as follows:
(i) Size is not regular and sedimentation values range from the 20S to 100S.
(ii) The base composition of hnRNA is likely to be DNA from which it is transcribed.
(iii) mRNA is prepared from hnRNA through enzymatic processing.