Which of these terms refers to a specific segment of DNA that contains the code for a polypeptide?

• A. Promoter
• B. Intron
• C. Exon
• D. Gene

Answer: (D)

The term that refers to a specific segment of DNA that contains the code for a polypeptide is a gene. Genes are fundamental units of heredity and serve as instructions for synthesizing proteins, which include polypeptides. Each gene comprises several nucleotides that are arranged in a specific sequence, ultimately encoding the information required to produce a particular polypeptide or protein.

While promoters are sequences that initiate the transcription of a gene, they do not themselves contain the code for a polypeptide. Introns are non-coding sequences within a gene that are transcribed but are later spliced out during mRNA processing, so they also do not contain the final coding information for polypeptides. Exons are the coding sequences of a gene that are expressed in the final mRNA; however, the term "gene" encompasses both exons and introns, making it the more accurate choice for describing the overall segment of DNA responsible for coding a polypeptide.