How could you be sure you have located a section of DNA that encodes for a protein?

A DNA sequence that encodes a protein can be transcribed into RNA, and the RNA can then be translated to produce a protein. Seeing what protein results is the direct way to test whether the DNA section encodes one. Simply writing down the DNA sequence does not show that it is expressed, and comparing a faulty protein with DNA does not establish that the section produces a protein.

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