Organisms of all three domains of life usually use the mRNA codon AUG as the start codon.
Do organisms of the three domains use the same amino acid as the initial amino acid in translation? Identify similarities and differences.

Verified step by step guidance

1. Understand that the start codon AUG is universally recognized in all three domains of life (Bacteria, Archaea, and Eukarya) as the signal to initiate translation.
2. Recall that the AUG codon codes for the amino acid methionine (Met) in most cases, but the form of methionine used as the initial amino acid can vary between domains.
3. In Bacteria, the initial methionine is a modified form called N-formylmethionine (fMet), which is specifically used for the initiation of protein synthesis.
4. In Archaea and Eukarya, the initial methionine is not formylated; instead, it is a regular methionine (Met) that is incorporated at the start of translation.
5. Summarize the similarity: all three domains use AUG as the start codon and methionine as the initial amino acid. Highlight the difference: Bacteria use N-formylmethionine (fMet), while Archaea and Eukarya use unmodified methionine (Met).

Key Concepts

Start Codon

The start codon, AUG, is a specific sequence in mRNA that signals the beginning of translation. It codes for the amino acid methionine in eukaryotes and archaea, while in bacteria, it can also code for a modified form called N-formylmethionine. Understanding the role of the start codon is crucial for grasping how protein synthesis initiates across different organisms.

Translation Initiation

Translation initiation is the first step in protein synthesis, where the ribosome assembles around the mRNA and the first tRNA molecule binds to the start codon. This process varies slightly among the three domains of life—bacteria, archaea, and eukaryotes—due to differences in ribosomal structure and initiation factors, which can affect the initial amino acid incorporated into the growing polypeptide chain.

Amino Acids and Genetic Code

Amino acids are the building blocks of proteins, and the genetic code determines how sequences of nucleotides in mRNA are translated into amino acids. While AUG universally codes for methionine in eukaryotes and archaea, bacteria use it to code for N-formylmethionine, highlighting both similarities and differences in the translation process across the three domains of life.