Learning Objectives
- Identify the universal Start Codon and its amino acid products.
- Contrast the start amino acids in Prokaryotes versus Eukaryotes.
- Master the three Stop Codons and their role in termination.
- Understand the clinical significance of fMet in the immune response.
1. The Start Codon: AUG
Translation always begins at the AUG codon. While the codon is the same for both domains of life, the initial amino acid differs.
- Mnemonic: AUG inAUGurates protein synthesis.
- Eukaryotes: Codes for Methionine. This is often cleaved off before the protein is fully processed.
- Prokaryotes: Codes for N-formylmethionine (fMet).
Clinical High-Yield:
Because fMet is unique to bacteria and mitochondria, its presence in the body acts as a beacon for the immune system. It directly stimulates neutrophil chemotaxis, drawing white blood cells to the site of infection.
Because fMet is unique to bacteria and mitochondria, its presence in the body acts as a beacon for the immune system. It directly stimulates neutrophil chemotaxis, drawing white blood cells to the site of infection.
2. The Stop Codons
Termination occurs when the ribosome encounters one of three stop codons. These do not code for amino acids; instead, they are recognized by Release Factors.
| Codon | Mnemonic |
|---|---|
| UGA | U Go Away |
| UAA | U Are Away |
| UAG | U Are Gone |
3. Summary Table
| Feature | Prokaryotes | Eukaryotes |
|---|---|---|
| Start Codon | AUG | AUG |
| Initial Amino Acid | fMet (Formyl-methionine) | Methionine |
| Stop Codons | UGA, UAA, UAG | UGA, UAA, UAG |
Activity
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