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Codon Chart

The continuity of life is made possible by the storage, replication and transcription of genetic code from one generation of life forms to the other in the form of DNA and RNA in some cases. The subject of this article is the codon chart which is an important piece of reference when it comes to understanding DNA and RNA transcription, as well as the creation of the 20 amino acids. Before we talk about codon charts, let us understand what we mean by a codon. That will enable you to understand how to decipher the codon tables provided below.

What is a Codon?
DNA (Deoxyribonucleic Acid) is the molecule which contains all the genetic code of an organism. DNA is the blueprint from which all the proteins that make body functions possible are created. Consider the entire genetic code to be a book. This book is unique in the sense that it is written using just four alphabets which are nucleotides. The words in this book are all entirely three letter words formed from these four nucleotide letters and they are called codons! Adenine, Guanine, Cytosine and Thymine (A, G, C, T) are the four nucleotides that form codons in the DNA. While in RNA (Ribonulciec Acid) molecule, genetic code is made up of the four letter A, G, C, U. In RNA, Thymine is replaced by Uracil. Read more on difference between DNA and RNA.

The four nucleotides form 64 triplet combinations or codons. So the entire genetic code is written using just 64 words! Each one of the codons encodes one of the 20 different amino acids. Amino acids are the building blocks of proteins. More than one codon can translate into the same amino acid. A gene is a segment of DNA which is a series of codons that contains information about synthesis of proteins. Transcription is the process of reading a gene and extracting information from it for protein synthesis.

The start of DNA transcription or DNA translation of a gene is signaled by the start codon which is unique for RNA and DNA. There are stop codons too which signal the end of transcription. The information about synthesis of every gene is read from the DNA in the cell nucleus and transferred in the form of messenger RNA segments to the exterior cytoplasm. In there, with the help of tRNA (transport RNA molecules), the proteins are synthesized with the right amino acid sequences.

The DNA codon chart and RNA codon chart that I present below details the various nucleotide combinations that create the 20 known amino acids. There is redundancy in the coding as more than one nucleotide combination can lead to the creation of the same amino acid.

RNA Codon Chart
If you are studying or planning to study biochemistry, you will eventually study the role of mRNA (messenger RNA) in DNA transcription of the cell. The starting codon for mRNA is AUG. Here is a codon chart that lists the various combination of nucleotides that lead to creation of the 20 known amino acids.

Amino Acid / Start-Stop Codon Codon (Nucleotide Triplet Combinations)
Phenylalanine (Phe) (UUU, UUC)
Leucine (Leu) (UUA, UUG, CUU,CUC, CUA, CUG)
Methionine (Met) / Start Codon (AUG)
Valine (Val) (GUU, GUC, GUA, GUG)
Serine (Ser) (UCU, UCC, UCA, UCG, AGU, AGC)
Proline (Pro) (CCU, CCC, CCA, CCG)
Threonine (Thr) (ACU, ACC, ACA, ACG)
Alanine (Ala) (GCU, GCC, GCA, GCG)
Tyrosine (Tyr) (UAU, UAC)
Histidine (His) (CAU, CAC)
Glutamine (Gln) (CAA, CAG)
Asparagine (Asn) (AAU, AAC)
Lysine (Lys) (AAA, AAG)
Aspartic Acid (Asp) (AAU, GAU, GAC)
Glutamic Acid (Glu) (CAA, GAA, GAG)
Cysteine (Cys) (UGU, UGC)
Tryptophan (Trp) (UGG)
Arginine (Arg) (CGU, CGC, CGA, CGG, AGA, AGG)
Serine (Ser) (UCU, UCC, UCA, UCG, AGU, AGC)
Glycine (Gly) (GGU, GGC, GGA, GGG)
Isoleucine (Ile) (AUU, AUC, AUA)
Stop Codon (UAA, UAG, UGA)

DNA Codon Chart
The DNA codon chart is different from the RNA codon table as it contains Thymine (which is known as Thymidine when combined with deoxyribose) in place of Uracil (which is known as Uridine when in combination with ribose). In DNA, the starting codon is ATG which signals the intiation of translation. Here is the DNA codon chart which is exactly the same as the RNA chart if U is only replaced by T.

Amino Acid / Start-Stop Codon Codon (Nucleotide Triplet Combinations)
Phenylalanine (Phe) (TTT, TTC)
Leucine (Leu) (TTA, TTG, CTT,CTC, CTA, CTG)
Methionine (Met) / Start Codon (ATG)
Valine (Val) (GTT, GTC, GTA, GTG)
Serine (Ser) (TCT, TCC, TCA, TCG, AGT, AGC)
Proline (Pro) (CCT, CCC, CCA, CCG)
Threonine (Thr) (ACT, ACC, ACA, ACG)
Alanine (Ala) (GCT, GCC, GCA, GCG)
Tyrosine (Tyr) (TAT, TAC)
Histidine (His) (CAT, CAC)
Glutamine (Gln) (CAA, CAG)
Asparagine (Asn) (AAT, AAC)
Lysine (Lys) (AAA, AAG)
Aspartic Acid (Asp) (AAT, GAT, GAC)
Glutamic Acid (Glu) (CAA, GAA, GAG)
Cysteine (Cys) (TGT, TGC)
Tryptophan (Trp) (TGG)
Arginine (Arg) (CGT, CGC, CGA, CGG, AGA, AGG)
Serine (Ser) (TCT, TCC, TCA, TCG, AGT, AGC)
Glycine (Gly) (GGT, GGC, GGA, GGG)
Isoleucine (Ile) (ATT, ATC, ATA)
Stop Codon (TAA, TAG, TGA)

These codon charts are useful references for anyone studying DNA transcription. Deciphering the genetic code is a tough job however. Scientists are in a stage now where they have the entire DNA sequence decoded, but most of it doesn’t make sense. It is like having a printed book in your hand but not being able to read as a lot of it sounds gibberish. There remains a lot more to be known in human genetics as it is vastly unexplored territory. This is good news for those of you who are exploring this field as a career option.

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