In the process of translation, the formation of proteins from mRNA involves multiple steps that take place within the ribosome—a complex molecular machine in the cell. The translation process initiates when:
- The small subunit of the ribosome binds to the mRNA. This initial binding is crucial as it sets the stage for the correct alignment and reading of the mRNA coding sequence.
- The process begins in the cytoplasm where the small subunit of the ribosome attaches to the mRNA near the start codon (AUG), positioning it correctly for the translation to begin.
Once the small subunit is bound to the mRNA, the following steps occur:
- The appropriate initiator tRNA molecule, which carries methionine, pairs with the start codon on the mRNA.
- This pairing attracts the larger subunit of the ribosome to form a complete ribosome, creating the P (peptidyl) and A (aminoacyl) sites.
This correctly juxtaposed configuration of ribosomal subunits and mRNA prepares for elongation—the next phase of translation, where tRNAs sequentially add amino acids to the growing polypeptide chain, following the codon sequence present on the mRNA.
Therefore, contrary to other options, the translation's precise start is marked by the initial encounter and binding of the small ribosomal subunit to mRNA.