aloitusaminohappo

Aloitusaminohappo, also known as the start codon, is a specific nucleotide sequence within messenger RNA (mRNA) that signals the beginning of protein synthesis. In most organisms, this sequence is AUG, which also codes for the amino acid methionine. When the ribosome encounters the AUG codon during translation, it initiates the process of building a polypeptide chain by recruiting the first tRNA carrying methionine. This methionine is often removed from the newly formed protein after synthesis is complete, but its presence is crucial for initiating the translation process.

The start codon is not just a signal for initiation; it also establishes the reading frame for the subsequent codons. The genetic code is read in triplets of nucleotides, and the start codon determines where the first triplet begins. Any shift in this reading frame, caused by insertions or deletions of nucleotides, would result in a completely different sequence of amino acids being incorporated into the protein, likely rendering it non-functional. In some cases, alternative start codons like GUG or UUG can be used, but AUG is by far the most common in all domains of life. The precise recognition and binding of the initiator tRNA to the start codon is a highly regulated step, ensuring that protein synthesis begins at the correct location on the mRNA molecule.