RNA Translation: the synthesis of a protein. (Lewis, 3) The biosynthesis of peptides and proteins on ribosomes, directed by messenger RNA, via transfer RNA. (MeSH)
The process in which messenger RNA is transported out of the “nucleus” and delivered to a "ribosome," itself composed of RNA and "proteins," where the information in the sequence of the "messenger RNA" will be used to generate a new protein molecule. "Transfer RNA’s," complementary to each “base pair” triplet “codon” in the messenger RNA, deliver “amino acids” which are bonded together to form a protein chain. (Watson, 77-78) The information within a gene is ultimately translated into the sequence of amino acids in a "polypeptide." Translation requires many cellular components including a ribosome and two types of RNA molecules. (Brooker, 69) If the protein is "synthesized" on a 'free ribosome’ (one that is free floating in the "cytoplasm"), it will probably be used in the cell. If the protein is synthesized on a ribosome that is located on the “endoplasmic reticulum” it will probably be placed in a “vesicle,” move through the “smooth ER” and the “golgi apparatus” for processing, and then be transported outside the cell. (RNA translation) interprets one language into another language - "nucleic acid" language into amino acid language. (Norman, 7/22/09) Also referred to as 'translation,' 'protein translation,' and 'genetic translation.'
RNA Translation Stages: the stages of protein synthesis in which the code on the mRNA molecule is used to control the production of a polypeptide chain by a ribosome. (Indge, 274) Editor’s note - RNA translation stages listed below in order of occurrence.
RNA Translation Initiation: mRNA strand becomes attached to the (ribosome) “small subunit.” The “large subunit” "binds" to the top of the small subunit with mRNA sandwiched between. (Norman, 7/22/09)
Single Recognition Particle: a protein/RNA complex that has two functions. First, it recognizes the endoplasmic reticulum (ER) signal sequence and pauses translation. Second, it binds to a "receptor" in the endoplasmic reticulum membrane, which docks the ribosome over a “channel.” At this stage the single recognition particle is released and translation resumes. (Brooker, 117) Also referred to as 'initiation.'
RNA Translation Elongation: mRNA is ‘read’ by the ribosome one codon at a time beginning at start sequence ‘AUG.’ Multiple ribosomes are working on a mRNA strand simultaneously. Each codon (3 nucleotides long) is translated into one amino acid. Marshall Nirenberg discovered the first codon (UUU) in 1961. (Norman, 7/22/09) Also referred to as 'elongation.'
RNA Translation Translocation: tRNA retrieves amino acid, with matching nucleic acid codon, from the cytoplasm and brings it to the large ribosome subunit, where it attaches to the ‘A-site’. A peptide bond forms between an amino acid on the polypeptide already in the ‘P-site,’ and the new amino acid. The polypeptide is transferred to the A-site. The ribosome moves one codon to the right. The now ‘amino acid-less” tRNA is released from the ‘E-site’ (‘exit site’). This process is repeated again and again until a stop codon (UAA, UGA, or UAG) is reached. (Norman, 7/22/09) Also referred to as 'translocation.'
RNA Translation Termination: a protein 'releasing factor’ binds to the ‘A’ site. This hydrolyzes the bond at the P-site breaking it, and the newly synthesized polypeptide is released. The ribosome subunits, mRNA, and releasing factor, dissociate. Note as the mRNA strand is being translated into amino acids, the polypeptides being produced are assuming structural "conformation." Note for proteins destined for the “ER” - during protein synthesis, the new protein is bound by the ‘signal recognition particle (SRP)’, which, in turn, binds to an ‘SRP receptor’ in the ER membrane. This anchors the ribosome to the ER. Note the polypeptide chains have an “N-terminus” and a “C-terminus.” (COOH) (Norman, 7/22/09) Also referred to as 'termination.'