Our DNA (deoxyribonucleic acid) is our instruction manual. It is composed of a sequence of letters (nucleotides – A, T, C, and G) that give rise to proteins, the functional elements of our organism. For this purpose, DNA needs to be read, interpreted, and translated. This is where a process called translation comes into play.
Phase 1: DNA Transcription
Before starting to produce proteins, the cell needs to make a temporary copy of the gene from which it will extract the information. This process comes before translation and is known as transcription. During transcription, the DNA information is copied into a molecule called messenger RNA (mRNA), which serves as a guide to generate proteins. The instructions in the mRNA are grouped in threes, forming what are known as nucleotide triplets or codons. Each codon corresponds to a specific element (amino acid) in the protein.
Phase 2: Initiation of DNA Translation
One of the main characters in translation is the ribosome, responsible for reading the mRNA and joining the amino acids in the correct order to form a protein.
To initiate the translation process, all the “pieces” of the ribosome must assemble. The ribosome is made up of two subunits. The small subunit binds to the 5’ end of the mRNA and moves along it until it finds the start codon (AUG). This codon marks the beginning of the protein and serves as a guide to identify which part of the DNA corresponds to a new protein.
To incorporate the different amino acids into the protein chain, the participation of transfer RNA (tRNA) is required, which acts as an adapter between the mRNA and the growing amino acid chain. Its function is to attach the corresponding amino acid to the protein chain that is being synthesized.
Once the tRNA carrying the first amino acid of the protein (methionine) binds to the start codon, the large ribosomal subunit joins in. At that moment, the functional ribosome is formed, which is responsible for carrying out the translation.
Phase 3: Elongation of DNA Translation
Once translation has started, the ribosome moves along the mRNA to synthesize the corresponding protein. During the elongation phase, and thanks to the coordinated action of the functional ribosome and the tRNA, the polypeptide chain is progressively extended through the various sites of the ribosome. This process follows a repetitive cycle:
- A new tRNA enters the A site of the ribosome, where its anticodon pairs with the corresponding codon on the mRNA, introducing a new amino acid.
- A peptide bond is formed between the newly incorporated amino acid and the polypeptide chain located at the P site.
- The tRNA, now without its amino acid, moves to the E site and is released from the ribosome.
In each cycle, the ribosome moves one position along the mRNA, allowing the tRNA located in the P site to move to the E site and be released, while the tRNA in the A site shifts to the P site. In this way, a new tRNA can enter the A site. This mechanism repeats codon by codon, incorporating one amino acid at each step, until a stop codon or termination codon is reached, signaling the end of the process.
Phase 4: Termination of DNA Translation
When the ribosome encounters a stop codon (UAA, UAG, or UGA), there is no corresponding tRNA. Instead, a release factor binds to the A site and triggers the release of the peptide chain.
The protein folds into its functional form and is then free to carry out its role in the organism. On the other hand, the ribosome disassembles, ready to begin another round.
