Question

The coding sequence which appears in mature RNA is:
(A) Exon
(B) Intron
(C) Cistron
(D) Splicing

Answer 1

Hint: During the process of transcription, only one DNA strand transcribes to form ss RNA. Once the process is complete it undergoes post-transcriptional modification where splicing occurs. After the process of splicing, introns are removed and mature RNA consists of exons only. Only exons can code for proteins.
 Step by step solution:

Cistron is the part of DNA which can code for specific polypeptides in protein synthesis. DNA segment which has one cistron is called monocistronic and which has more than one Cistron is known as polycistronic. Cistron is often used as an alternate term for the gene (but both are not completely the same), so option (C) is not the correct answer.
Newly formed RNA from DNA contains both introns and exons, after a process known as splicing introns are removed and mature RNA contains only exons. Immature RNA is also known as hn RNA or precursor mRNA. Introns have no role in protein synthesis, their presence is a primitive character and thus is also known as reminiscent of antiquity. A process called splicing is used to remove introns from hn RNA and form fully processed mature RNA. The RNA formed after splicing participates in protein synthesis, mature RNA contains exons so therefore exons are used in protein synthesis.

Therefore, the correct option is (A).
Both hnRNA and mRNA both of these are RNA and contain ribonucleotide as their basic unit, the only difference is that hn RNA is the precursor of mRNA, and hnRNA forms or becomes mRNA after splicing.