6.2.3—Transcription and translation roles

Protein synthesis converts genetic information into an amino-acid sequence through two linked stages: transcription makes an mRNA copy from a DNA template, and translation reads the mRNA to assemble a polypeptide.

1. Transcription — DNA template to mRNA: The relevant DNA region is used as a template. RNA polymerase joins complementary RNA nucleotides to make a single-stranded mRNA molecule containing codons. The DNA sequence remains the information source; mRNA is the transportable message.
2. Message to ribosome: The mRNA leaves the nucleus and attaches to a ribosome. The ribosome reads the mRNA codons in order from the defined start point.
3. tRNA matching: Each tRNA carries a specific amino acid and has an anticodon. Its anticodon pairs with the complementary mRNA codon, bringing the corresponding amino acid to the ribosome.
4. Translation — chain assembly: The ribosome positions successive tRNAs so peptide bonds form between adjacent amino acids. The chain lengthens in the order specified by the mRNA codons.
5. Completion: Translation stops when a stop codon is reached. The completed amino-acid chain is released and can fold into the particular polypeptide structure specified by its sequence.

The information is converted rather than moved unchanged: DNA base sequence → mRNA codons → tRNA anticodon matching → amino-acid order → polypeptide. Transcription separates the protected DNA information source from the message, while translation converts the message into a peptide-bonded chain at the ribosome.

Transcription produces RNA, not a polypeptide; translation reads mRNA, not DNA directly. tRNA brings amino acids and uses anticodons, whereas mRNA carries codons. Staff-only visual brief retained in the Topic Blueprint: show DNA → mRNA → ribosome, tRNA delivery and chain growth; no image is generated or bound here.