why AUG where be a start codon
The AUG codon serves as the start codon in most organisms. Start codons are specific sequences of three nucleotides (in this case, Adenine-Uracil-Guanine or AUG) that indicate the beginning of a protein-coding sequence in mRNA. The AUG codon also codes for the amino acid Methionine, which is often the first amino acid incorporated into a growing polypeptide chain during translation. Additionally, cellular machinery recognizes and binds to the AUG codon to initiate the process of protein synthesis.
The start codon in genetic code is typically represented by the sequence "AUG". This codon, which stands for methionine, serves as the initiation signal for protein synthesis. Here is why "AUG" is considered as the start codon:
1. Universal Usage: The start codon "AUG" is found in the genetic code of both prokaryotes and eukaryotes, making it a universally recognized signal for protein synthesis initiation.
2. Methionine: The "AUG" codon encodes the amino acid methionine. Methionine is often the first amino acid incorporated into a growing polypeptide chain during protein synthesis.
3. Initiates Translation: When a ribosome binds to the mRNA molecule during translation, it seeks a start codon to initiate the synthesis of a polypeptide chain. The "AUG" codon serves as the recruitment site for the ribosome, ensuring the protein synthesis process begins at the right place.
4. Alternative Start Codons: While "AUG" is the most common start codon, some alternative start codons, such as "GUG" and "UUG", can also initiate translation in certain contexts. These alternative start codons usually code for different amino acids, rather than methionine.
In summary, the "AUG" codon is considered the start codon because it is widely recognized across different organisms and serves as the beginning point for protein synthesis.
The start codon AUG is indeed an important component in the process of protein synthesis. It serves as the initiation signal for the translation of messenger RNA (mRNA) into a protein. When the mRNA molecule is being read by the ribosome, the presence of the AUG start codon triggers the assembly of the ribosome and the binding of the initiator transfer RNA (tRNA) molecule, carrying the amino acid methionine.
Now, you may be wondering why AUG was chosen as the start codon. The reason lies in its association with the amino acid methionine. Methionine is usually the first amino acid incorporated during protein synthesis, hence the choice of the AUG codon as the start codon. However, there are some exceptions where alternative start codons, such as GUG and UUG, can also initiate translation and lead to the incorporation of other amino acids.
To understand why AUG was identified as the start codon, we need to consider how it was discovered. Scientists conducted experiments using synthetic mRNAs with different nucleotide sequences and observed which combinations led to the initiation of protein synthesis. Through such experiments, they determined that AUG was the most common and effective start codon in many organisms.
In conclusion, the choice of the AUG codon as the start codon is based on experimental evidence showing its effectiveness in initiating protein synthesis. Its association with the amino acid methionine also plays a role in its selection.