What is a Start Codon?
The initial set of codons in an mRNA transcript that is translated by a ribosome is known as the start codon. In eukaryotes, the start codon typically is AUG, as it the first codon in the transcribed mRNA that undergoes translation. It codes for the amino acid methionine (Met) in eukaryotes and formyl methionine (fMet) in prokaryotes. However, there are exceptions, such as in the case of the fungi, Saccharomyces cerevisiae, where GUG is used as a start codon and in case of Candida albicans where CAG is used as a start codon.
During protein synthesis, the tRNA recognizes the Start codon AUG with the help of some initiation factors and starts translation of mRNA. Generally, the starting sequence is preceded by the 5’UTR (untranslated region). Some alternative start codons are found in both prokaryotes and eukaryotes. Since they employ a different initiator tRNA when acting as start codons, alternative codons typically code for amino acids other than methionine. It has been discovered that E. Coli uses AUG 83%, GUG 14%, and UUG 3% as start codons in prokaryotes.
Also Read: Translation of RNA to Protein
Difference between Start Codon and Stop Codon
Start and stop codons are two punctuation marks of the genetic code that signal the beginning and end of protein synthesis. The main difference between the start and stop codon is that the start codon marks the site at which translation into protein sequence begins whereas the stop codon marks the site at which translation ends. The most common start codon is AUG which codes for methionine while there are three stop codons UAG, UAA, and UGA, and they do not code for an amino acid.
Table of Content
- Differences between the Start codon and Stop codon
- What is Genetic code?
- What is a Start Codon?
- What is a Stop Codon?
- Similarities Between Start Codon and Stop Codon
- Conclusion: Difference between Start Codon and Stop Codon