Advertisement
Incontrovertible Evidence for the Unity of All Life
The basic building blocks of the genetic code are universal. In essence, every single unicellular and multicellular life form, that has ever existed on Earth, has had a genome, made up of the same nucleotide subunits (A, T/U, C, G). This clearly proves the common origin of all life on our planet.
DNA (Deoxyribonucleic Acid) is the molecule that contains all the genetic code of an organism. It is the recipe book, referred by cells, to produce proteins that make body functions possible. This book is unique, in the sense that it is written using just four alphabets, which are nucleotides. It is entirely written with three-letter words, called codons. Adenine, Guanine, Cytosine, and Thymine (A, G, C, T) are the four nucleotides (or letters) that form codons (or words) in the DNA. In RNA (Ribonucleic Acid) molecule, the genetic code is made up of the four letters, Adenine, Guanine, Cytosine, and Uracil (A, G, C, U).

The four nucleotides form 64 (= 43) triplet combinations or codons. So the entire genetic code is written using just 64 different words. Each one of the codons encodes one of the 20 different amino acids. To be precise, among the 64 codons, 61 encode amino acids (including the initiation codon in RNA, which is AUG). The rest of three act as stop codons, that terminate the transcription process. More than one codon can translate into the same amino acid, which is a building block of proteins. Here is a RNA/DNA codon translator, that will directly provide you with the amino acid associated with a particular nucleotide triplet combination.

RNA/DNA Codon Translator
Enter Nucleotide Triplet Combination

A gene is a segment of DNA, which is a series of codons that contains information about synthesis of a single or more proteins. Transcription is the process of reading a gene and extracting information from it, for protein synthesis.

The start of DNA transcription of a gene is signaled by the start codon. Stop codons 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 (mRNA) segments, to the exterior cytoplasm. In there, with the help of tRNA (transport RNA molecules), the ribosomes synthesize proteins, with the right amino acid sequences.

The DNA and RNA codon charts presented below, detail the various nucleotide combinations that create the 20 known amino acids. There is redundancy in the coding, as more than one nucleotide combination maps 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 chart that lists the various combinations of nucleotides which lead to creation of the 20 known amino acids.

* Click on the image to print your copy.

RNA Codon Chart

Amino Acid / Start-Stop CodonCodon (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)(GAU, GAC)
Glutamic Acid (Glu)(GAA, GAG)
Cysteine (Cys)(UGU, UGC)
Tryptophan (Trp)(UGG)
Arginine (Arg)(CGU, CGC, CGA, CGG, AGA, AGG)
Glycine (Gly)(GGU, GGC, GGA, GGG)
Isoleucine (Ile)(AUU, AUC, AUA)
Stop Codon(UAA, UAG, UGA)

DNA Codon Chart

The chart for DNA codons is different from RNA, 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). This DNA codon table is obtained by substituting 'T' in place of 'U' in the RNA codon table and is exactly identical to it. If you want to verify its correspondence with the RNA table, first substitute every T, with U.

* Click on the image to print your copy.

DNA Codon Chart

Amino Acid / Start-Stop CodonCodon (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)(GAT, GAC)
Glutamic Acid (Glu)(GAA, GAG)
Cysteine (Cys)(TGT, TGC)
Tryptophan (Trp)(TGG)
Arginine (Arg)(CGT, CGC, CGA, CGG, AGA, AGG)
Glycine (Gly)(GGT, GGC, GGA, GGG)
Isoleucine (Ile)(ATT, ATC, ATA)
Stop Codon(TAA, TAG, TGA)

Other than the two full sets of DNA, existent in every human body cell, there is an inherited genetic component, that is not contained in the cell nucleus, but resides in the mitochondria. In humans, mitochondrial DNA (mtDNA) is directly inherited from mother to son/daughter and is made up of about 16,600 nucleotide bases, and it encodes 37 genes. The codon translation in this organelle differs from the standard code slightly.

In the mammalian mitochondria, the AGA and AGG codons act as stop codons, instead of translating into Arginine. Also, AUA maps to Methionine in mtDNA, instead of Isoleucine, and the UGA codon translates into Tryptophan, instead of acting as a stop codon, as it normally does, in nuclear DNA.

These 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 human 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 a vastly unexplored territory. This is good news for those of you, who are exploring this field as a career option.