What do we need to make proteins ? The process of translation , or protein synthesis , involves the decoding of an mRNA message into individual amino acids that are then strung together to form polypeptides - or proteins - ranging in length from 50 to more than 1,000 amino acids .
Transfer RNAs ( tRNA ) tRNAs bind to codon sequences on the mRNA template and add the corresponding amino acid to the growing polypeptide chain . tRNAs carry a series of nucleotides , called anticodons , that allow them to match up with complementary mRNA codons . For example , if the sequence GAG occurred on an mRNA template , it would be bound by a tRNA expressing the anticodon CUC ( complementary sequence ), and the amino acid glutamic would be subsequently added to the polypeptide chain . tRNAs are the molecules that actually ' translate ' mRNA into proteins .
Many molecules and macromolecules |
contribute to the process of translation . |
In addition to the mRNA template , |
translation |
requires |
the |
input |
of |
ribosomes , |
tRNAs , |
and |
various |
enzymes . |
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Ribosomes Ribosomes are found in the cytoplasm in prokaryotes and in both the cytoplasm and rough endoplasmic reticulum in eukaryotes . When they are not synthesizing proteins , ribosomes are dissociated into two subunits , large and small . The units reassociate with the initiation of translation . The small subunit is responsible for binding the mRNA template , and the large subunit binds tRNAs . mRNA is simultaneously translated by many ribosomes .
The complete mRNA / poly-ribosome structure is called a polysome .
Aminoacyl tRNA Synthetases Every tRNA molecule is linked to its correct amino acid by a group of enzymes called aminoacyl tRNA synthetases . At least one type of aminoacyl tRNA synthetase exists for each of the 20 amino acids .