A series of codons in part of a mRNA molecule. Each codon consists of three nucleotides, representing a single amino acid.

The genetic code is the set of rules by which information encoded in genetic material (DNA or RNA sequences) is translated into proteins (amino acid sequences) by living cells. Specifically, the code defines a mapping between tri-nucleotide sequences called codons and amino acids; every triplet of nucleotides in a nucleic acid sequence specifies a single amino acid. Because the vast majority of genes are encoded with exactly the same code (see #RNA codon table), this particular code is often referred to as the canonical or standard genetic code, or simply the genetic code, though in fact there are many variant codes; thus, the canonical genetic code is not universal. For example, in humans, protein synthesis in mitochondria relies on a genetic code that varies from the canonical code. Animation of a section of DNA rotating. ... Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... The interaction of mRNA in a eukaryote cell. ... A nucleotide is a chemical compound that consists of a heterocyclic base, a sugar, and one or more phosphate groups. ... This article is about the class of chemicals. ... The structure of part of a DNA double helix Deoxyribonucleic acid, or DNA, is a nucleic acid molecule that contains the genetic instructions used in the development and functioning of all known living organisms. ... Left: An RNA strand, with its nitrogenous bases. ... Translation is the second stage of protein biosynthesis (part of the overall process of gene expression). ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... This article is about the class of chemicals. ... Drawing of the structure of cork as it appeared under the microscope to Robert Hooke from Micrographia which is the origin of the word cell being used to describe the smallest unit of a living organism Cells in culture, stained for keratin (red) and DNA (green) The cell is the... A nucleotide is a chemical compound that consists of a heterocyclic base, a sugar, and one or more phosphate groups. ... For other uses, see Gene (disambiguation). ... Electron micrograph of a mitochondrion showing its mitochondrial matrix and membranes In cell biology, a mitochondrion (plural mitochondria) is a membrane-enclosed organelle that is found in most eukaryotic cells. ...

Cracking the genetic code

The genetic code

After the structure of DNA was deciphered by James Watson, Francis Crick, Maurice Wilkins and Rosalind Franklin, serious efforts to understand the nature of the encoding of proteins began. George Gamov postulated that a three-letter code must be employed to encode the 20 different amino acids used by living cells to encode proteins (because 3 is the smallest n such that 4ⁿ is at least 20). The fact that codons did consist of three DNA bases was first demonstrated in the Crick, Brenner et al. experiment. The first elucidation of a codon was done by Marshall Nirenberg and Heinrich J. Matthaei in 1961 at the National Institutes of Health. They used a cell-free system to translate a poly-uracil RNA sequence (or UUUUU... in biochemical terms) and discovered that the polypeptide they had synthesized consisted of only the amino acid phenylalanine. They thereby deduced from this poly-phenylalanine that the codon UUU specified the amino-acid phenylalanine. Extending this work, Nirenberg and his coworkers were able to determine the nucleotide makeup of each codon. In order to determine the order of the sequence, trinucleotides were bound to ribosomes and radioactively labeled aminoacyl-tRNA was used to determine which amino acid corresponded to the codon. Nirenberg's group was able to determine the sequences of 54 out of 64 codons. Subsequent work by Har Gobind Khorana identified the rest of the code, and shortly thereafter Robert W. Holley determined the structure of transfer RNA, the adapter molecule that facilitates translation. In 1968, Khorana, Holley and Nirenberg shared the Nobel Prize in Physiology or Medicine for their work. Image File history File links GeneticCode21. ... Image File history File links GeneticCode21. ... There is more than one person with the name James Watson: James Watson, participant in the Battle of the Little Bighorn James Watson, author of the novel Talking in Whispers James Watson, U.S. Senator from New York (1797-1801) James Watson, painter of 77 portraits held by the U... Francis Harry Compton Crick OM FRS (8 June 1916 – 28 July 2004) was an English molecular biologist, physicist, and neuroscientist, who is most noted for being one of the co-discoverers of the structure of the DNA molecule in 1953. ... Maurice Hugh Frederick Wilkins CBE FRS (15 December 1916 – 5 October 2004) was a New Zealand-born British molecular biologist, and Nobel Laureate who contributed research in the fields of phosphorescence, radar, isotope separation, and X-ray diffraction. ... Rosalind Elsie Franklin (25 July 1920 Kensington, London – 16 April 1958 Chelsea, London) was an English biophysicist and crystallographer who made important contributions to the understanding of the fine structures of DNA, viruses, coal and graphite. ... George Gamow (pronounced GAM-off) (March 4, 1904 – August 19, 1968) , born Georgiy Antonovich Gamov (Георгий Антонович Гамов) was a Ukrainian born physicist and cosmologist. ... This article is about the class of chemicals. ... This article or section is in need of attention from an expert on the subject. ... Marshall Nirenberg won a Nobel Prize in 1968 Marshall Warren Nirenberg (born April 10, 1927) was a U.S. biochemist and geneticist. ... This article needs to be cleaned up to conform to a higher standard of quality. ... National Institutes of Health Building 50 at NIH Clinical Center - Building 10 The National Institutes of Health (NIH) is an agency of the United States Department of Health and Human Services and is the primary agency of the United States government responsible for biomedical research. ... A cell-free system is a widely-used in vitro tool used to study biological reactions that happen within a cell with less of the complex interactions found in a whole cell. ... Translation is the second stage of protein biosynthesis (part of the overall process of gene expression). ... Peptides are the family of molecules formed from the linking, in a defined order, of various amino acids. ... Phenyl alanine is an α-amino acid with the formula HO2CCH(NH2)CH2C6H5. ... Har Gobind Khorana (born January 9, 1922) is an American molecular biologist born of Indian Punjabi heritage in British India. ... Robert W. Holley, the structure of a tRNA is shown in the background Dr Robert W. Holley (January 28, 1922 - February 11, 1993) was an American biochemist, he was awarded the Nobel Prize in Physiology or Medicine in 1968 for describing the structure of alanine transfer RNA, linking DNA and... Transfer RNA Transfer RNA (abbreviated tRNA), first hypothesized by Francis Crick, is a small RNA chain (73-93 nucleotides) that transfers a specific amino acid to a growing polypeptide chain at the ribosomal site of protein synthesis during translation. ... The Nobel Prizes (Swedish: ), as designated in Alfred Nobels will in 1895, are awarded for physics, chemistry, physiology or medicine, literature, and peace. ...

Transfer of information via the genetic code

The genome of an organism is inscribed in DNA, or in some viruses RNA. The portion of the genome that codes for a protein or an RNA is referred to as a gene. Those genes that code for proteins are composed of tri-nucleotide units called codons, each coding for a single amino acid. Each nucleotide sub-unit consists of a phosphate, deoxyribose sugar and one of the 4 nitrogenous nucleotide bases. The purine bases adenine (A) and guanine (G) are larger and consist of two aromatic rings. The pyrimidine bases cytosine (C) and thymine (T) are smaller and consist of only one aromatic ring. In the double-helix configuration, two strands of DNA are joined to each other by hydrogen bonds in an arrangement known as base pairing. These bonds almost always form between an adenine base on one strand and a thymine on the other strand and between a cytosine base on one strand and a guanine base on the other. This means that the number of A and T residues will be the same in a given double helix as will the number of G and C residues. In RNA, thymine (T) is replaced by uracil (U), and the deoxyribose is substituted by ribose. In biology the genome of an organism is the whole hereditary information of an organism that is encoded in the DNA (or, for some viruses, RNA). ... The structure of part of a DNA double helix Deoxyribonucleic acid, or DNA, is a nucleic acid molecule that contains the genetic instructions used in the development and functioning of all known living organisms. ... Left: An RNA strand, with its nitrogenous bases. ... For other uses, see Gene (disambiguation). ... A phosphate, in inorganic chemistry, is a salt of phosphoric acid. ... Deoxyribose Deoxyribose, also known as D-Deoxyribose and 2-deoxyribose, is an aldopentose — a monosaccharide containing five carbon atoms, and including an aldehyde functional group. ... A nucleotide is a chemical compound that consists of a heterocyclic base, a sugar, and one or more phosphate groups. ... Purine is a heterocyclic aromatic organic compound, consisting of a pyrimidine ring fused to an imidazole ring. ... For the programming language Adenine, see Adenine (programming language). ... Guanine is one of the five main nucleobases found in the nucleic acids DNA and RNA; the others being adenine, cytosine, thymine, and uracil. ... Pyrimidine is a heterocyclic aromatic organic compound similar to benzene and pyridine, containing two nitrogen atoms at positions 1 and 3 of the six-member ring [1]. It is isomeric with two other forms of diazine. ... Cytosine is one of the 5 main nucleobases used in storing and transporting genetic information within a cell in the nucleic acids DNA and RNA. It is a pyrimidine derivative, with a heterocyclic aromatic ring and two substituents attached (an amine group at position 4 and a keto group at... For the similarly-spelled vitamin compound, see Thiamine Thymine, also known as 5-methyluracil, is a pyrimidine nucleobase. ... Base pairs, of a DNA molecule. ... Uracil is a pyrimidine which is common and naturally occurring. ... Ribose Ribose, primarily seen as D-ribose, is an aldopentose — a monosaccharide containing five carbon atoms, and including an aldehyde functional group. ...

Each protein-coding gene is transcribed into a template molecule of the related polymer RNA, known as messenger RNA or mRNA. This in turn is translated on the ribosome into an amino acid chain or polypeptide. The process of translation requires transfer RNAs specific for individual amino acids with the amino acids covalently attached to them, guanosine triphosphate as an energy source, and a number of translation factors. tRNAs have anticodons complementary to the codons in mRNA and can be "charged" covalently with amino acids at their 3' terminal CCA ends. Individual tRNAs are charged with specific amino acids by enzymes known as aminoacyl tRNA synthetases which have high specificity for both their cognate amino acids and tRNAs. The high specificity of these enzymes is a major reason why the fidelity of protein translation is maintained. A micrograph of ongoing gene transcription of ribosomal RNA illustrating the growing primary transcripts. ... The life cycle of an mRNA in a eukaryotic cell. ... Translation is the second process of protein biosynthesis (part of the overall process of gene expression). ... Figure 1: Ribosome structure indicating small subunit (A) and large subunit (B). ... This article is about the class of chemicals. ... Peptides (from the Greek πεπτος, digestible), are the family of short molecules formed from the linking, in a defined order, of various α-amino acids. ... Transfer RNA Transfer RNA (abbreviated tRNA), first hypothesized by Francis Crick, is a small RNA chain (73-93 nucleotides) that transfers a specific amino acid to a growing polypeptide chain at the ribosomal site of protein synthesis during translation. ... Covalent bonding is a form of chemical bonding characterized by the sharing of one or more pairs of electrons between atoms, in order to produce a mutual attraction, which holds the resultant molecule together. ... Guanosine triphosphate (GTP) is also known as guanosine-5-triphosphate. ... An aminoacyl tRNA synthetase (abbreviated aaRs) is an enzyme that catalyzes the binding of a specific amino acid to a tRNA to form an aminoacyl-tRNA. The synthetase hydrolyzes ATP to bind the appropriate amino acid to the 3 hydroxyl of the tRNA molecule. ...

There are 4³ = 64 different codon combinations possible with a triplet codon of three nucleotides. In reality, all 64 codons of the standard genetic code are assigned for either amino acids or stop signals during translation. If, for example, an RNA sequence, UUUAAACCC is considered and the reading-frame starts with the first U (by convention, 5' to 3'), there are three codons, namely, UUU, AAA and CCC, each of which specifies one amino acid. This RNA sequence will be translated into an amino acid sequence, three amino acids long. A comparison may be made with computer science, where the codon is the equivalent of a byte, which codes for a single letter in a program (like one amino acid of a protein), and a nucleotide for a bit. In biology, a reading frame is a contiguous and non-overlapping set of three-nucleotide codons in DNA or RNA. There are 3 possible reading frames in a mRNA strand and six in a double stranded DNA molecule. ... The structure of part of a DNA double helix Deoxyribonucleic acid, or DNA, is a nucleic acid molecule that contains the genetic instructions used in the development and functioning of all known living organisms. ... Computer science, or computing science, is the study of the theoretical foundations of information and computation and their implementation and application in computer systems. ... In computer science a byte (pronounced bite) is a unit of measurement of information storage, most often consisting of eight bits. ... BIT is an acronym for: Bannari amman Institute of Technology Bangalore Institute of Technology Beijing Institute of Technology Benzisothiazolinone Bilateral Investment Treaty Bhilai Institute of Technology - Durg Birla Institute of Technology - Mesra Battles in Time (Doctor Who magazine) BIT International College, formerly the Bohol Institute of Technology in Bohol, Philippines...

The standard genetic code is shown in the following tables. Table 1 shows what amino acid each of the 64 codons specifies. Table 2 shows what codons specify each of the 20 standard amino acids involved in translation. These are called forward and reverse codon tables, respectively. For example, the codon AAU represents the amino acid asparagine, and UGU and UGC represent cysteine (standard three-letter designations, Asn and Cys respectively). ! For other articles using the abbreviation or acronym asn see ASN. Asparagine is one of the 20 most common natural amino acids on Earth. ... Cysteine is a naturally occurring, sulfur-containing amino acid that is found in most proteins, although only in small quantities. ...

RNA codon table

Salient features

Reading frame of a sequence

Note that a codon is defined by the initial nucleotide from which translation starts. For example, the string GGGAAACCC, if read from the first position, contains the codons GGG, AAA and CCC; and if read from the second position, it contains the codons GGA and AAC; if read starting from the third position, GAA and ACC. Partial codons have been ignored in this example. Every sequence can thus be read in three reading frames, each of which will produce a different amino acid sequence (in the given example, Gly-Lys-Pro, Gly-Asp, or Glu-Thr, respectively). With double-stranded DNA there are six possible reading frames, three in the forward orientation on one strand and three reverse (on the opposite strand). RNA codons. ... In biology, a reading frame is a contiguous and non-overlapping set of three-nucleotide codons in DNA or RNA. There are 3 possible reading frames in a mRNA strand and six in a double stranded DNA molecule. ... In biology, a reading frame is a contiguous and non-overlapping set of three-nucleotide codons in DNA or RNA. There are 3 possible reading frames in a mRNA strand and six in a double stranded DNA molecule. ...

The actual frame a protein sequence is translated in is defined by a start codon, usually the first AUG codon in the mRNA sequence. Mutations that disrupt the reading frame by insertions or deletions of a non-multiple of 3 nucleotide bases are known as frameshift mutations. These mutations may impair the function of the resulting protein, if it is formed, and are thus rare in in vivo protein-coding sequences. Often such misformed proteins are targeted for proteolytic degradation. In addition, a frame shift mutation is very likely to cause a stop codon to be read which truncates the creation of the protein (example [2]). One reason for the rareness of frame-shifted mutations being inherited is that if the protein being translated is essential for growth under the selective pressures the organism faces, absence of a functional protein may cause lethality before the organism is viable. ATG and AUG denote sequences of DNA and RNA respectively that are the start codon or initiation codon encoding the amino acid methionine (Met) in eukaryotes and a modified Met (fMet) in prokaryotes. ... A frameshift mutation (also called a frameshift or a framing error) is a genetic mutation that inserts or deletes a number of nucleotides that is not evenly divisible by three from a DNA sequence. ... In vivo (Latin for (with)in the living). ...

Start/stop codons

Translation starts with a chain initiation codon (start codon). Unlike stop codons, the codon alone is not sufficient to begin the process. Nearby sequences and initiation factors are also required to start translation. The most common start codon is AUG, which codes for methionine, so most amino acid chains start with methionine. ATG and AUG denote sequences of DNA and RNA respectively that are the start codon or initiation codon encoding the amino acid methionine (Met) in eukaryotes and a modified Met (fMet) in prokaryotes. ... Biological and artificial methods for creation of proteins differ significantly. ...

The three stop codons have been given names: UAG is amber, UGA is opal (sometimes also called umber), and UAA is ochre. "Amber" was named by discoverers Richard Epstein and Charles Steinberg after their friend Harris Bernstein, whose last name means "amber" in German. The other two stop codons were named 'ochre" and "opal" in order to keep the "color names" theme. Stop codons are also called termination codons and they signal release of the nascent polypeptide from the ribosome due to binding of release factors in the absence of cognate tRNAs with anticodons complementary to these stop signals.^[2] RNA codons. ... The release factor is a protein that recognises the termination codon or stop codon in a mRNA sequence. ...

Degeneracy of the genetic code

The genetic code has redundancy but no ambiguity. For example, although codons GAA and GAG both specify glutamic acid (redundancy), neither of them specifies any other amino acid (no ambiguity). Degenerate codons may differ in their third positions; e.g., both GAA and GAG code for the amino acid glutamic acid. A codon is said to be fourfold degenerate if any nucleotide at its third position specifies the same amino acid; it is said to be twofold degenerate if only two of four possible nucleotides at its third position specify the same amino acid. In twofold degenerate codons, the equivalent third position nucleotides are always either two purines (A/G) or two pyrimidines (C/T). Only two amino acids are specified by a single codon; one of these is the amino-acid methionine, specified by the codon AUG, which also specifies the start of translation; the other is tryptophan, specified by the codon UGG. The degeneracy of the genetic code is what accounts for the existence of silent mutations. Glutamic acid (Glu, E), is the protonated form of glutamate (the anion). ... Purine is a heterocyclic aromatic organic compound, consisting of a pyrimidine ring fused to an imidazole ring. ... Pyrimidine is a heterocyclic aromatic organic compound similar to benzene and pyridine, containing two nitrogen atoms at positions 1 and 3 of the six-member ring [1]. It is isomeric with two other forms of diazine. ... Methionine is an α-amino acid with the chemical formula HO2CCH(NH2)CH2CH2SCH3. ... Tryptophan is an essential amino acid involved in human nutrition. ... Silent mutations or synonymous mutations are DNA mutations that, although they alter a particular codon, they do not alter the final amino acid, and hence do not affect the final protein. ...

Degeneracy results because a triplet code designates 20 amino acids and a stop codon. Because there are four bases, triplet codons are required to produce at least 21 different codes. For example, if there were two bases per codon, then only 16 amino acids could be coded for (4²=16). Because at least 21 codes are required, then 4³ gives 64 possible codons, meaning that some degeneracy must exist.

These properties of the genetic code make it more fault-tolerant for point mutations. For example, in theory, fourfold degenerate codons can tolerate any point mutation at the third position, although codon usage bias restricts this in practice in many organisms; twofold degenerate codons can tolerate one out of the three possible point mutations at the third position. Since transition mutations (purine to purine or pyrimidine to pyrimidine mutations) are more likely than transversion (purine to pyrimidine or vice-versa) mutations, the equivalence of purines or that of pyrimidines at twofold degenerate sites adds a further fault-tolerance. A point mutation, or substitution, is a type of mutation that causes the replacement of a single base nucleotide with another nucleotide. ... Codons are triplets of nucleotides that together specify an amino acid residue in a polypeptide chain. ... In genetics, a Transition is a mutation changing a purine to another purine nucleotide (A <-> G) or a pyrimidine to another pyrimidine nucleotide (C <-> T). ... In molecular biology, Transversion refers to the substitution of a purine for a pyrimidine or vice versa. ...

A practical consequence of redundancy is that some errors in the genetic code only cause a silent mutation or an error that would not affect the protein because the hydrophilicity or hydrophobicity is maintained by equivalent substitution of amino acids; for example, a codon of NUN (where N = any nucleotide) tends to code for hydrophobic amino acids. Even so, it is a single point mutation that causes a modified hemoglobin molecule in sickle-cell disease. The hydrophilic glutamate (Glu) is substituted by the hydrophobic valine (Val), which reduces the solubility of β-globin. In this case, this mutation causes hemoglobin to form linear polymers linked by the hydrophobic interaction between the valine groups causing sickle-cell deformation of erythrocytes. Sickle-cell disease is generally not caused by a de novo mutation. Rather it is selected for in malarial regions (in a way similar to thalassemia), as heterozygous people have some resistance to the malarial Plasmodium parasite (heterozygote advantage). The adjective hydrophilic describes something that likes water (from Greek hydros = water; philos = friend). ... In chemistry, hydrophobic or lipophilic species, or hydrophobes, tend to be electrically neutral and nonpolar, and thus prefer other neutral and nonpolar solvents or molecular environments. ... Structure of hemoglobin. ... Sickle-cell disease is a group of genetic disorders caused by sickle hemoglobin (Hgb S or Hb S). ... Glutamate is the anion of glutamic acid. ... Valine is an amino acid that cannot be synthesized by humans, so it is considered an essential amino acid for human life. ... Structure of hemoglobin. ... For linguistic mutation, see Apophony. ... Malaria is a vector-borne infectious disease caused by protozoan parasites. ... Thalassemia (British spelling, thalassaemia) is an inherited autosomal recessive blood disease. ... It has been suggested that this article be split into multiple articles accessible from a disambiguation page. ... Species Plasmodium achiotense Plasmodium achromaticum Plasmodium acuminatum Plasmodium adunyinkai Plasmodium aegyptensis Plasmodium aeuminatum Plasmodium agamae Plasmodium anasum Plasmodium anomaluri Plasmodium arachniformis Plasmodium ashfordi Plasmodium atheruri Plasmodium aurulentum Plasmodium australis Plasmodium attenuatum Plasmodium azurophilum Plasmodium balli Plasmodium bambusicolai Plasmodium basilisci Plasmodium beebei Plasmodium beltrani Plasmodium berghei Plasmodium bertii Plasmodium bigueti Plasmodium... A heterozygote advantage (heterozygous advantage or overdominance) describes the case in which the heterozygote genotype has a higher relative fitness than either the homozygote dominant or homozygote recessive genotype. ...

These variable codes for amino acids are allowed because of modified bases in the first base of the anticodon of the tRNA, and the base-pair formed is called a wobble base pair. The modified bases include inosine and the Non-Watson-Crick U-G basepair. An anticodon is a unit made up of nucleotides that plays an important role in various DNA cycles, including DNA transcription. ... Wobble base pairs for inosine Wobble base pairs for Uracil A wobble base pair is a G-U and I-U / I-A / I-C pair fundamental in RNA secondary structure. ... Inosine is a molecule (known as a nucleoside) that is formed when hypoxanthine is attached to a ribose ring (also known as a ribofuranose) via a β-N9-glycosidic bond. ...

Variations to the standard genetic code

While slight variations on the standard code had been predicted earlier,^[3] none were discovered until 1979, when researchers studying human mitochondrial genes discovered they used an alternative code. Many slight variants have been discovered since,^[4] including various alternative mitochondrial codes,^[5] as well as small variants such as Mycoplasma translating the codon UGA as tryptophan. In bacteria and archaea, GUG and UUG are common start codons. However, in rare cases, certain specific proteins may use alternative initiation (start) codons not normally used by that species.^[6] // Mitochondrial genetics is the study of the genetics of the DNA contained in mitochondria. ... Species M. genitalium M. hominis M. pneumoniae etc. ... Phyla Actinobacteria Aquificae Chlamydiae Bacteroidetes/Chlorobi Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Lentisphaerae Nitrospirae Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Verrucomicrobia Bacteria (singular: bacterium) are unicellular microorganisms. ... Phyla Crenarchaeota Euryarchaeota Korarchaeota Nanoarchaeota ARMAN The Archaea (), or archaebacteria, are a major group of microorganisms. ...

In certain proteins, non-standard amino acids are substituted for standard stop codons, depending upon associated signal sequences in the messenger RNA: UGA can code for selenocysteine and UAG can code for pyrrolysine as discussed in the relevant articles. Selenocysteine is now viewed as the 21st amino acid, and pyrrolysine is viewed as the 22nd. A detailed description of variations in the genetic code can be found at the NCBI web site. Skeletal formula of L-selenocysteine Space-filling model of L-selenocysteine Selenocysteine is an amino acid that is present in several enzymes (for example glutathione peroxidases, tetraiodothyronine 5 deiodinases, thioredoxin reductases, formate dehydrogenases, glycine reductases and some hydrogenases). ... Pyrrolysine is a naturally-occurring genetically-coded amino acid. ...

However, all known codes have strong similarities to each other, and the coding mechanism is the same for all organisms: three-base codons, tRNA, and ribosomes, reading the code in the same direction, translating the code three letters at a time into sequences of amino acids.

Theories on the origin of the genetic code

Despite the variations that exist, the genetic codes used by all known forms of life on Earth are very similar. Since there are many possible genetic codes that are thought to have similar utility to the one used by Earth life, the theory of evolution suggests that the genetic code was established very early in the history of life and meta-analysis of transfer RNA suggest it was established soon after the formation of earth. This article is about evolution in biology. ...

One can ask the question: is the genetic code completely random, just one set of codon-amino acid correspondences that happened to establish itself and be "frozen in" early in evolution, although functionally any of the many other possible transcription tables would have done just as well? Already a cursory look at the table shows patterns that suggest that this is not the case.

There are three themes running through the many theories that seek to explain the evolution of the genetic code (and hence the origin of these patterns).^[7] One is illustrated by recent aptamer experiments which show that some amino acids have a selective chemical affinity for the base triplets that code for them.^[8] This suggests that the current, complex translation mechanism involving tRNA and associated enzymes may be a later development, and that originally, protein sequences were directly templated on base sequences. Another is that the standard genetic code that we see today grew from a simpler, earlier code through a process of "biosynthetic expansion". Here the idea is that primordial life 'discovered' new amino acids (e.g. as by-products of metabolism) and later back-incorporated some of these into the machinery of genetic coding. Although much circumstantial evidence has been found to suggest that fewer different amino acids were used in the past than today,^[9] precise and detailed hypotheses about exactly which amino acids entered the code in exactly what order has proved far more controversial.^[10][11] A third theory is that natural selection has led to codon assignments of the genetic code that minimize the effects of mutations.^[12]. Aptamers are oligo nucliec acid or peptide molecules selected from large randome sequence pool to bind to specific target molecule. ... Transfer RNA (abbreviated tRNA) is a small RNA chain (74-93 nucleotides) that transfers a specific amino acid to a growing polypeptide chain at the ribosomal site of protein synthesis during translation. ... For other uses, see Natural selection (disambiguation). ... This article is about mutation in biology, for other meanings see: mutation (disambiguation). ...

References

The interaction of mRNA in a eukaryote cell. ...

See also

• Crick, Brenner et al. experiment
• Anticodon
• Protein biosynthesis
• Operon
• Lac operon
• Epigenetic code
• Har Gobind Khorana

This article or section is in need of attention from an expert on the subject. ... An anticodon is a unit made up of nucleotides that plays an important role in various DNA cycles, including DNA transcription. ... An overview of protein synthesis. ... An operon is a group of key nucleotide sequences including an operator, a common promoter, and one or more structural genes that are controlled as a unit to produce messenger RNA (mRNA). ... The lac operon is an operon required for the transport and metabolism of lactose in Escherichia coli and some other enteric bacteria. ... The epigenetic code is hypothesized to be a defining code in every eukaryotic cell consisting of the specific epigenetic modification in each cell. ... Har Gobind Khorana (born January 9, 1922) is an American molecular biologist born of Indian Punjabi heritage in British India. ...

Further reading

• Griffiths, Anthony J.F.; Miller, Jeffrey H.; Suzuki, David T.; Lewontin, Richard C.; Gelbart, William M. (1999). Introduction to Genetic Analysis (7th ed.). New York: W. H. Freeman & Co. ISBN 0-7167-3771-X
• Alberts, Bruce; Johnson, Alexander; Lewis, Julian; Raff, Martin; Roberts, Keith; Walter, Peter. (2002). Molecular Biology of the Cell (4th ed.). New York: Garland Publishing. ISBN 0-8153-3218-1
• Lodish, Harvey; Berk, Arnold; Zipursky, S. Lawrence; Matsudaira, Paul; Baltimore, David; Darnell, James E. (1999). Molecular Cell Biology (4th ed.). New York: W. H. Freeman & Co. ISBN 0-7167-3706-X

External links

• The Genetic Codes → Genetic Code Tables
• Online DNA → Amino Acid Converter
• DNA Sequence → Protein Sequence converter
• DNA to protein translation (6 frames/13 genetic codes)
• The Codon Usage Database → Codon frequency tables for many organisms
• Evolving Code - a themed wiki devoted to the topic of how the genetic code evolved, and its effects on the subsequent evolution of the genome.