Structural genes are composed of which parts?

• A. Intron and exon
• B. Exon only
• C. Promoter and terminator
• D. Intron only

Answer: (A)

Structural genes are the coding segments within a gene, and in many organisms these coding parts are arranged with noncoding sequences in between. Exons are the portions that carry the information used to make the final product, while introns are the noncoding sequences transcribed first but removed during RNA processing. After splicing, the exons come together to form the mature mRNA that will be translated into protein. The promoter and terminator are regulatory elements that control transcription, not part of the coding structure of the gene itself. So, a structural gene comprises both exons and introns.