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Name: Veronica
Status: student
Grade: other
Location: Outside U.S.
Country: Malaysia
Date: Fall 2011

Why are there more than one codon to produce the same amino acid?

Hi Veronica,

I think the best answer has to do with what happens in the case of a mutation. If something goes "wrong" in the process, having some redundancy helps to minimize the harm done to the organism by any errors in the translation and transcription process. Having multiple codons is one example

Here's a little more detail: There are more three-letter combinations than there are in-use amino acids, so just from a pure numbers standpoint, you have more "addresses" than you have "houses". So the question is, what should you do with the 'extras'? One option is for the extra codons to do "nothing". If the codon does 'nothing', that means that if a mutation occurs, or some error in translation occurs, then the protein would be terminated. A half of a protein is almost certainly going to be non-functional, and could be fatal for the organism if it's a critical protein. The other option is for the codons to code "something" which might be the same amino acid, or it might be a different one. If the error results in the same amino acid, the organism will be unharmed; but even if it's a different amino acid, it's possible the protein will still work (or work partially, or even be superior) -- but it's more likely to at least not be fatal the way the truncated protein might be.

Hope this helps, Burr

Hi Veronica,

Genetic code is degenerate code, meaning that some codons may have similar functions or produce the same output. Hence some amino acids will have more than one codon.

Good example: Leucine has codons CUU, CUC, CUA, CUG. You can almost say that Leucine is CUx, where x is any ribonucleotide base.

All have the same function and produce the same output.

Hope that helps.

-Alex Viray

Different codons can potentially code for the same amino acid. This is known as degeneracy. Degeneracy acts as a kind of fault tolerance against point mutations. Point mutations are nucleotide swaps that occur during DNA replication.

A single point mutation can result in an amino acid substitution. This can modify or inactivate the intended function of the resulting protein. For example, the 6th codon on the HBB gene is supposed to be GAA. This codes for glutamic acid. If it undergoes a single point mutation to GTA (coded as GUA on the mRNA), valine is produced instead, leading to sickle cell anemia!

In general, a point mutation could also result in a stop codon, which would prematurely truncate the resulting protein.

Degeneracy acts as a hedge against this to some extent. If the codon changes, the final amino acid (and, by extension, protein) can still remain the same. This is known as a “silent mutation” – although one of the underlying nucleotides has changed, the end product remains unchanged.

Dr. Tim Durham Instructor, Office of Curriculum and Instruction University Colloquium Department of Biological Sciences Florida Gulf Coast University

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