Question

Assertion :Transcription unit is often monocistronic in eukaryotes and polycistronic in prokaryotes . Reason: Exons do not appear in mature RNA, introns appear in mature RNA.

• A. Assertion and Reason are true, Reason is correct explanation of Assertion.
  
• B. Assertion and Reason are true, Reason is not the correct explanation of Assertion.
  
• C. Assertion is true, Reason is false.
  
• D. Assertion is false, Reason is true.

Answer 1

The correct option is C Assertion is true, Reason is false.

The prokaryotic mRNAs are polycistronic which means that multiple genes are present on a single transcript and the single promoter initiates transcription of all those genes and regulates their expression. They have multiple initiation and termination codons and thus translate more than one protein. Eukaryotic mRNAs are monocistronic which are transcribed from the single gene and thus carry single initiation and termination codons thereby coding for the single polypeptide. The assertion is correct.

The protein coding part of eukaryotic DNA is exon while the gene sequences that are present between exons and do not code for any protein product are called introns. Each exon carries a part of the reading frame and thus carries information of a part of encoded polypeptide which means that it is both transcribed and translated. Introns of the transcript are removed by splicing to produce mature mRNA which means that introns are transcribed but not translated. The reason is false.
Therefore, the correct answer is option C.