The translation

Translation understandable explained ...

In the course of translation, proteins are synthesized by reading the mRNA previously produced in the transcription. Translation means "to translate," and indeed, the genetic code is "translated" into protein chains.

The place where this process takes place in the cell is the ribosome.

But first, let's take a closer look at the mRNA strand: it consists of a long chain of bases. Three consecutive bases (base triplet / codon) always encode a particular amino acid (which triplets which amino acid codons can be read in the codon).

One distinguishes between the start codon, normal codons and the stop codons. The translation will always start 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).

"Normal" codons are all other base triplets that are neither start nor stop codon and each encode a particular amino acid. Also, the start codon AUG encodes an amino acid (methionine) in contrast to the three stop codons, which are really only responsible for completing the translation.

The task of tRNA (transfer RNA) is to transport the individual amino acids to the ribosome and then combine them with another amino acid to form peptide chains.

tRNA consists of several arms. An amino acid binds to one of these arms, and on the opposite arm is an anticodon that matches the corresponding base codon of the mRNA. Example: The tRNA for methionine possesses the anticodon UAC; this only fits the base triplet AUG in the mRNA. Thus, the base sequence AUG encodes the amino acid methionine in the mRNA.

There are far more tRNAs available: each of the amino acids needs a specific tRNA to be delivered to the corresponding codon on the mRNA. Because every tRNA is always responsible for only one amino acid, corresponding to its anticodon.

Back to the ribosome: At the start codon, the first tRNA attaches to the mRNA (because the start codon is AUG, the first annealing tRNA has accordingly taken up the amino acid methionine). This is followed by a second tRNA with a specific amino acid, which attaches next to the first tRNA. A peptide bond provides for linking of the two adjacent amino acids. Thereupon, the first tRNA leaves the ribosome without an amino acid, which is now at the end of the arm of the second tRNA together with its amino acid.

The third tRNA 'flies' along with the specific amino acid and attaches itself to the mRNA. The process is repeated until a base triplet appears in the mRNA that encodes a stop codon. For stop codons, there are no suitable tRNAs, so that the resulting peptide chain is then detached.

Codontable ordered by amino acids

Number      Amino Acid         Codon
1                  Methionine          AUG (start codon)
1                  Tryptophan          UGG
2                  Tyrosine                UAU UAC
2                  Phenylalanine      UUU UUC
2                  Cysteine ​​               UGU UGC
2                  Asparagin             AAU AAC
2                  Aspartic acid        GAU GAC
2                  Glutamine            CAA CAG
2                  Glutamic acid       GAA GAG
2                  Histidine               CAU CAC
2                  lysine                     AAA AAG
3                  Isoleucine             AUU AUC AUA
4                  Glycine                  GGU GGC GGA GGG
4                  Alanine                 GCU GCC GCA GCG
4                  Valin                      GUU GUC GUA GUG
4                  Threonine             ACU ACC ACA ACG
4                  Proline                  CCU CCC CCA CCG
6                  leucine                  CUU CUC CUA CUG UUA UUG
6                  Serine                    UCU UCC UCA UCG AGU AGC
6                  Arginine                CGU CGC CGA CGG AGA AGG
3                  No amino acids    UAA UAG UGA (stop codons)

Summary

During translation, the mRNA strand is read and a polypeptide chain is synthesized