Conversion of the information of the mRNA (the base sequence) into a protein (an amino acid sequence). Each three nucleotides of the mRNA encode an amino acid. This is bound to a specific transfer RNA (= tRNA) and is transported to the ribosome where it is converted into protein molecules.
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Translation
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A distinction is made between:
- the start codon
- normal codons and
- the stop codons.
Translation will always begin at the start codon AUG (base triplet consisting of adenine, uracil and guanine) and end at one of the three stop codons (UGA, UAA or UAG).
All other base triplets that are neither start nor stop codons and each encode a specific amino acid are referred to as "normal" codons. The start codon AUG also codes for an amino acid (methionine). The three stop codons are only responsible for terminating translation. They do not encode an amino acid.
The first tRNA (transfer RNA) now attaches to the mRNA at the start codon (the start codon is AUG and the first attaching tRNA accordingly takes up the amino acid methionine). The tRNA has the task of transporting the individual amino acids to the ribosome and then linking them to another amino acid. This sequence results in a peptide chain.
The tRNA consists of several arms. One arm binds an amino acid. The anticodon, which matches the corresponding base codon of the mRNA, is located on the other arm.
Example: The tRNA for methionine has the anticodon UAC; this only matches the base triplet AUG in the mRNA. This means that the base sequence AUG in the mRNA codes for the amino acid methionine.
Each tRNA is only responsible for one amino acid at a time, analogous to its anticodon. This means that each amino acid requires a specific tRNA in order to be transferred to the corresponding codon on the mRNA. This is followed by a second tRNA with a corresponding amino acid, which is attached next to the first tRNA. A peptide bond is formed between the two amino acids. After attachment of the amino acid, the first tRNA leaves the ribosome. The attached amino acid is now located at the end of the arm of the second tRNA together with its amino acid. Furthermore, a third tRNA together with a specific amino acid attaches to the mRNA. The process is repeated until a base triplet encoding a stop codon appears in the mRNA. There is no suitable tRNA for stop codons, so that the resulting peptide chain is now detached. The polypeptide strand is finalized.