Protein translation is the process by which a protein is created from a ribonucleic acid (RNA) template code. The strand of RNA, which contains the order for the protein’s amino acid sequence, binds to a special cellular organelle called a ribosome. This ribosome moves down the RNA strand, reads the code, and synthesizes the protein by adding one amino acid at a time. Once completed, the ribosome detaches from the RNA, and the RNA is either degraded by the cell or used again to make another protein. The newly synthesized protein then must undergo folding to achieve its native structure, or natural three-dimensional shape.
Following the process of transcription, which creates the RNA strand from a template of deoxyribonucleic acid (DNA), protein translation is the final main step in protein biosynthesis. The recently created RNA strand will leave the cell’s nucleus and move into either the cytosol, the main interior space of the cell, or into the endoplasmic reticulum (ER), another compartment of the cell where protein translation occurs. There are ribosomes as well as free amino acids for protein biosynthesis in both of these locations. In the ER, the ribosomes are attached to the surface of the organelle membrane, while in the cytosol, the ribosomes are free.
After the ribosome binds to the RNA, the phase of protein activation is started. During this phase, the ribosome’s large subunit binds covalently to the RNA strand. Next, small proteins called initiation factors also bind to the ribosome, allowing its small subunit to bind to the RNA and begin the protein initiation phase. The complex is now ready to begin building the protein.
Each of the three nucleotides on the RNA strand code for one specific amino acid, and the protein is created in the order of amino acids listed in the RNA code. The ribosome holds the RNA where three nucleotides bind to another molecule called transfer RNA (tRNA), which is a type of RNA molecule that is also bound to an amino acid. Once bound, the tRNA transfers its amino acid to the growing protein and leaves the complex, while the ribosome moves down the RNA strand to the next group of three nucleotides. This phase of protein translation is known as protein elongation, because during this phase the protein grows in length.
Protein termination is the end step of protein translation. During this phase the ribosome reaches the terminal RNA nucleotide code, known as the stop codon. Here, a protein called a release factor binds to the complex, freeing the ribosome, RNA strand, and newly created protein molecule.