Translation

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Translation involves taking the message that's in the messenger RNA and in a sense decoding the message from the language of nucleic acids to the language of proteins or polypeptides. For translation to happen, the messenger RNA goes to the cytoplasm where it is attached to a cellular structure called a ribosome. Ribosomes are two part molecular assemblies consisting of various proteins plus a special kind of RNA called ribosomal RNA. Ribosomal RNA is involved in catalyzing some of the chemical reactions of translation.

In addition to the ribosome, another kind of RNA called tRNA carries amino acids to the mRNA when it is attached to a particular part of the ribosome's small subunit, called a binding site. A critical feature of mRNA and how it is translated is the fact that each three nucleotides in the mRNA is called a codon and it is the codon that is translated. Thus the sequence of codons corresponds to the sequence of amino acids in the polypeptide. You will see that the tRNA molecules have a set of three nucleotide bases at one end that are complementary to a corresponding codon. The bases on the tRNA are called the anti codon. This is critical because the anti codons make the connection between the codons and the correct amino acids that go with each codon.

Scientists have cracked the code involved in translation and given a stretch of mRNA can tell what the corresponding sequence of amino acids is. Learning how to do this was one of the two or three big advances in the 20th century and has laid the foundation for many advances in biotechnology as well as more basic biology such as the study of evolution.

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Sample mRNA transcript showing codons nucleotide triplets. Read from left to right. This mRNA has 5 codons. Press on the image to go to the next step!
mRNA from transcription


 
 
 
 
 
 
 
 
 
 
 
 
 
 


Step 1. Attachment of AUG start codon to first binding site on ribosome. tRNA with the anticodon UAC and carrying the amino acid methionine(MET) comes to binding site.

Step 1 translation binding to ribosome

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Step 2. Ribosome moves down one codon so that AUG codon is at the second binding side UCA codon at first binding site. tRNA for serine comes to first binding site.
step 2 translation

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Step 3. Amino acids Methionine and serine joined by a peptide bond, Ribosome moves over by another codon. The tRNA carrying glycine comes to the first binding site.
Step 3 translation

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Step 4. Glycine(GLY) is joined to the other amino acids by a peptide bond. The tRNA carrying threonine(THR) is now at the first binding site of the ribosome.

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Step 5. Threonine attached to the polypeptide by a peptide bond. Stop codon at the first binding site. 

step 5 translation
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Step 6. Stop codon tells the ribosome to release the polypeptide. The tRNA's pick up more amino acids from the cell cell's amino acid pool to participate in more protein synthesis. The mRNA sequence is often broken down by the cell and its nucleotides reused. Image links to top of page.

step 6 translation

 

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created 03/07/00 pgd