If you’re studying genetics, molecular biology, or a related field, chances are you’ll need to learn how to make a codon chart (also called codon table) to better understand the genetic code.
This type of diagram shows all possible codons – essential components of DNA and RNA molecules – and the amino acids they represent. By using a codon table you can translate genetic information into specific proteins. Let’s take a closer look at how it all works.
The genetic code and codons
To understand how to use a codon table, it is necessary to first know some basics of genetics.
The genetic code is the set of rules by which the information encoded in genetic material (DNA or RNA) is translated into proteins by living cells. This genetic code is universal, meaning it is consistent across all organisms, from bacteria to bacteria E.coli to complex eukaryotes. (Eukaryotic cells contain a nucleus surrounded by a membrane).
The genetic code is represented by codons, with each codon consisting of three nucleotides (a specific type of organic molecule). To represent the different nucleotides in each of these triplet codes, scientists use the letters U, C, A and G, which stand for uracil, cytosine, adenine and guanine – the four possible nucleotides in messenger RNA.
For example, a sequence for an mRNA molecule could be: AUG-GGU-CAA-UAA. Each of these codons corresponds to a specific amino acid.
Since there are four possible nucleotides, there are 64 possible codons.
What is a codon graph?
A codon diagram is a visual representation that maps each of the 64 codons to the corresponding amino acids or signals. There are two commonly used versions of codon diagrams or codon tables. One is a square or rectangle and the other is a circle.
A codon table is crucial for decoding an mRNA sequence into a chain of amino acids, the building blocks of proteins.
Specific codons and their corresponding amino acids
Using a codon table you can determine which codons belong to which amino acids and vice versa. For example:
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The amino acid asparagine (Asn) corresponds to AAU and AAC.
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The amino acid glutamine (Gln) corresponds to CAA and CAG.
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The amino acid glycine (Gly) corresponds to GGU, GGC, GGA and GGG.
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The amino acid methionine (With) is coded by AUG.
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The amino acid phenylalanine (Phe) is encoded by the codons UUU and UUC.
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The amino acid proline (Pro) corresponds to CCU, CCC, CCA and CCG.
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The amino acid valine (Val) is represented by GUU, GUC, GUA and GUG.
Multiple codons and redundancy
The genetic code exhibits redundancy, with multiple codons coding for the same amino acid. For example, GCU, GCC, GCA, and GCG all code for alanine. Because a change in the third nucleotide often does not change the amino acids, this redundancy is a protection against genetic mutations.
How to use a codon graph
Knowing how to read a codon diagram can help you determine which amino acids are encoded in a DNA sequence. Here are the steps:
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Identify the mRNA sequence. An mRNA sequence is a series of codons that you transcribe from DNA. Let’s go back to our example mRNA sequence of AUG-GGU-CAA-UAA.
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Find the start codon. The start codon is usually AUG, which stands for methionine, and signals the start of that specific protein synthesis sequence.
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Translate the codons into amino acids. Use the codon table to decode each subsequent codon into the corresponding amino acid.
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End at the stop codon. Translation continues until you encounter a stop codon (UAA, UAG, or UGA), which signals the end of the protein synthesis sequence.
Origin of the codon table
The codon map emerged from the pioneering work of mid-20th century molecular biologists. The discovery of the double helix structure of DNA by James Watson and Francis Crick in 1953 paved the way for understanding how genetic information is encoded and translated into proteins.
In the early 1960s, Marshall Nirenberg (who would later receive a Nobel Prize for his work on the genetic code) and Johannes Matthaei conducted experiments using synthetic RNA to direct the synthesis of proteins in cell-free systems.
The men’s work showed that specific codons correspond to specific amino acids, leading to the first deciphering of a codon (UUU for phenylalanine). This breakthrough laid the foundation for the complete codon table.
Further research by Nirenberg, Philip Leder, Har Gobind Khorana and others expanded on this initial discovery. Khorana’s work, particularly his use of synthetic RNA molecules with defined sequences, was instrumental in determining the assignments of the remaining codons.
By 1966, scientists had completely deciphered the genetic code, revealing that most amino acids are encoded by more than one codon, a property known as redundancy or degeneracy.
Significance in biology and medicine
In molecular biology, the codon map has allowed scientists to investigate the mechanisms of gene expression, regulation and mutation, allowing comparative studies between species. And in medicine, it helps scientists and doctors advance genetic research and develop therapeutic interventions.
In genetic science, the codon map enables the modification of genes for researchers studying disease mechanisms or producing therapeutic proteins. For example, recombinant DNA technology, which relies on the codon map, has led to the production of insulin, growth hormones and other biologically important substances.
The map is also crucial in the development of gene therapy, in which doctors correct or replace defective genes to treat genetic disorders.
Understanding codons also helps scientists design mRNA vaccines, such as those researchers have developed for COVID-19. By optimizing codon sequences for efficient protein expression in human cells, scientists can better guarantee the effectiveness of a vaccine.
We created this article using AI technology, then made sure it was fact-checked and edited by a HowStuffWorks editor.
Original article: Reading a codon graph and identifying amino acids
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