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Codons and Amino Acids
Name: Veronica
Status: student
Grade: other
Location: Outside U.S.
Country: Malaysia
Date: Fall 2011
Question:
Why are there more than one codon to produce the same amino acid?
Replies:
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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Update: June 2012
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