_____ are extra sequences of nucleotides that are not necessary to create the corresponding protein.

• A. Exons
• B. Promoters
• C. Enhancers
• D. Introns

Answer: (D)

Understanding how genes are organized and processed helps explain this. Genes contain coding regions called exons and noncoding regions called introns. Introns are transcribed into pre-mRNA but are removed during RNA splicing before translation, so they do not become part of the final mRNA that encodes the protein. That’s why they are described as extra sequences not necessary to create the protein. Exons are the portions that remain in the mature mRNA to specify the amino acid sequence. Promoters are DNA regions that recruit RNA polymerase to start transcription, and enhancers help boost transcription levels but aren’t themselves part of the protein-coding sequence. So the noncoding, intron sequences fit the description.