Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne 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



Click here to return to the Molecular Biology Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (help@newton.dep.anl.gov), or at Argonne's Educational Programs

NEWTON AND ASK A SCIENTIST
Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory