How to Translate MRNA to TRNA

By John Brennan
Uracil is a base in RNA.
uracil - rna image by Cornelia Pithart from Fotolia.com

Genes in DNA are like coded recipes for proteins. Cells transcribe these coded recipes onto an messenger RNA (mRNA) transcript and export it out of the nucleus into the cytoplasm of the cell. Here structures called ribosomes make proteins with the help of transfer RNAs (tRNAs). This process is called translation. If you're taking a general biology course or a genetics course, some classes may want you to take an mRNA sequence and figure out what sequence of tRNAs, and hence amino acids, it would code for.

Find the first place in the mRNA sequence where the start codon occurs. The start codon is AUG. AUG also codes for the amino acid methionine, so all proteins start with the amino acid methionine (or N-formylmethionine in bacteria).

Translate each mRNA codon into an amino acid using a genetic code table, which can be found online. Remember that a tRNA essentially acts as an adapter in translation. A tRNA is an RNA molecule with a three-base anticodon which is complementary to a given mRNA codon. As are always complementary to Us, and Cs are complementary to Gs. Each tRNA is attached to an amino acid, so the ribosome moves down the mRNA transcript, positioning a matching tRNA codon next to each mRNA codon and linking the amino acids before ejecting the tRNA. Since each codon has three bases, you'll move down the mRNA transcript three bases at a time. Write down each amino acid's name as you go.

Notice more than one mRNA codon can code for the same amino acid. That's because the third base of the tRNA doesn't have to bond as tightly to its opposite number in the mRNA transcript as the first two bases. The third codon position is called the wobble base-pair.

Stop translating once you reach a stop codon in the mRNA. There are three stop codons: UAA, UAG and UGA.

About the Author

Based in San Diego, John Brennan has been writing about science and the environment since 2006. His articles have appeared in "Plenty," "San Diego Reader," "Santa Barbara Independent" and "East Bay Monthly." Brennan holds a Bachelor of Science in biology from the University of California, San Diego.