Question

The portion of a eukaryotic gene which is transcribed but not translated is
A) Exon
B) Intron
C) Cistron
D) Codon

Answer 1

Hint: Transcription is a process of formation of RNA from DNA and translation is a process of protein synthesis in which sequence of amino acids are synthesized from messenger RNA molecule (also known as mRNA).

Complete answer: Introns are the noncoding region (that is they do not code for any protein) and exons are coding part of eukaryotic DNA.
Exons carry part of the reading frame. That means it carries part of the information of an encoded polypeptide. In the initial stage transcripted m RNA is known as heterogeneous RNA.
In the process of transcription along with exons and introns, the complete gene is copied into pre mRNA.
During RNA splicing, pre mRNA is converted into mRNA but in this process, only exons are joined and introns have the nonsense codon which cannot be translated hence they are removed.
Therefore mature mRNA is formed and that is translated into protein.

So, the correct answer is “Option B”.

Note: Cistrons are genes that have special behavior in the cis-trans test. Cistron is transcribed as well as translated. An m-RNA can be monocistronic (single cistron) or polycistronic (multiple cistrons) which is transcribed from a single gene or multiple gene and code for single or multiple proteins respectively.
Codons are set of three DNA or RNA molecule that specifies a particular amino acid.
DNA codons can be transcripted into mRNA. Then it can be translated into proteins.
Therefore, the codon can be transcribed as well as translated.