In molecular biology, the usual flow of genetic information is from DNA to RNA to protein.

• A. DNA to RNA to Protein
• B. RNA to DNA to Protein
• C. Protein to RNA to DNA
• D. DNA to Protein to RNA

Answer: (A)

Transcription followed by translation explains how genetic information moves from DNA to protein. DNA in the nucleus serves as the template to make messenger RNA during transcription. The mRNA carries the encoded instructions in codons, which the ribosome reads in the cytoplasm, with help from tRNAs bringing the corresponding amino acids, to assemble a polypeptide chain. This two-step process—DNA to RNA, then RNA to protein—is why the standard description is DNA to RNA to protein. Exceptions exist (such as reverse transcription in some viruses), but they don’t reflect the usual flow of information in most cellular biology.