Question

if an mrna is synthesisd with all differnt codons what is the minimum number of amino acids in tbe protein that is formed by mrna​

Answer 1

Answer:

Answers are misleading due to posttranslational modification. Recall that a protein is the finished, functional product. Often times amino acids such as from the methionine start codons are cleaved off during post-translational modification (typically done in the ER). This reduces your question to “what is the shortest protein that is derived from all of the different types of codons?” Even this is complicated because there are exceptions to the typical mammalian codons; UGA is typically a stop codon, but it can code for selenocysteine under certain circumstances. It’s semantically the same codon per its nucleotides, yet it codes for something different so the argument could be made.

For simplicity’s sake, let’s ignore wonky codons. We’re still left with the length of the shortest functional protein (a non-functional protein is technically a polypeptide, not a protein) derived from a gene containing all 64 (or 61 if you’re concerned about stop codons) codons. This gives us a starting point of 61 amino acids as others have said. Unfortunately, it’s not a very good starting point.

The reason I disagree with stated answers of 61–64 is that post-translational modification can involve truncation of amino acids. Additionally, splicing may lead to an mRNA that contained all codons when it was synthesized (the criteria given in the question) actually being a fraction of that size when it reaches a ribosome.

With all of this in mind, I’m guessing there’s a protein out there that's 30–40 amino acids long if not shorter that was either spliced down pretranslation or modified posttranslationally. Given the hundreds of billions of proteins out there, it’s not statistically reasonable to believe that there are none shorter than 61. Because there are hundreds of billions of proteins and we haven’t discovered but a tiny fraction of them, I can’t really give you a definitive answer but I’m confident in saying it’s much shorter than 61.

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