What do we call the sequence of nucleotides that codes for an amino acid?

The genetic code is a set of rules defining how the four-letter code of DNA is translated into the 20-letter code of amino acids, which are the building blocks of proteins. The genetic code is a set of three-letter combinations of nucleotides called codons, each of which corresponds to a specific amino acid or stop signal. The concept of codons was first described by Francis Crick and his colleagues in 1961. During the same year, Marshall Nirenberg and Heinrich Matthaei performed experiments that began deciphering the genetic code. They showed that the RNA sequence UUU specifically coded for the amino acid phenylalanine. Following this discovery, Nirenberg, Philip Leder, and Gobind Khorana identified the rest of the genetic code and fully described each three-letter codon and its corresponding amino acid.

There are 64 possible permutations, or combinations, of three-letter nucleotide sequences that can be made from the four nucleotides. Of these 64 codons, 61 represent amino acids, and three are stop signals. Although each codon is specific for only one amino acid (or one stop signal), the genetic code is described as degenerate, or redundant, because a single amino acid may be coded for by more than one codon. It is also important to note that the genetic code does not overlap, meaning that each nucleotide is part of only one codon-a single nucleotide cannot be part of two adjacent codons. Furthermore, the genetic code is nearly universal, with only rare variations reported. For instance, mitochondria have an alternative genetic code with slight variations.

• Entertainment & Pop Culture
• Geography & Travel
• Health & Medicine
• Lifestyles & Social Issues
• Literature
• Philosophy & Religion
• Politics, Law & Government
• Science
• Sports & Recreation
• Technology
• Visual Arts
• World History

• On This Day in History
• Quizzes
• Podcasts
• Dictionary
• Biographies
• Summaries
• Top Questions
• Week In Review
• Infographics
• Demystified
• Lists
• #WTFact
• Companions
• Image Galleries
• Spotlight
• The Forum
• One Good Fact

• Entertainment & Pop Culture
• Geography & Travel
• Health & Medicine
• Lifestyles & Social Issues
• Literature
• Philosophy & Religion
• Politics, Law & Government
• Science
• Sports & Recreation
• Technology
• Visual Arts
• World History

• Britannica Classics
  Check out these retro videos from Encyclopedia Britannica’s archives.
• Britannica Explains
  In these videos, Britannica explains a variety of topics and answers frequently asked questions.
• Demystified Videos
  In Demystified, Britannica has all the answers to your burning questions.
• #WTFact Videos
  In #WTFact Britannica shares some of the most bizarre facts we can find.
• This Time in History
  In these videos, find out what happened this month (or any month!) in history.

• Student Portal
  Britannica is the ultimate student resource for key school subjects like history, government, literature, and more.
• COVID-19 Portal
  While this global health crisis continues to evolve, it can be useful to look to past pandemics to better understand how to respond today.
• 100 Women
  Britannica celebrates the centennial of the Nineteenth Amendment, highlighting suffragists and history-making politicians.
• Britannica Beyond
  We’ve created a new place where questions are at the center of learning. Go ahead. Ask. We won’t mind.
• Saving Earth
  Britannica Presents Earth’s To-Do List for the 21st Century. Learn about the major environmental problems facing our planet and what can be done about them!
• SpaceNext50
  Britannica presents SpaceNext50, From the race to the Moon to space stewardship, we explore a wide range of subjects that feed our curiosity about space!

The standard RNA codon table organized in a wheel

A codon table can be used to translate a genetic code into a sequence of amino acids.[1][2] The standard genetic code is traditionally represented as an RNA codon table, because when proteins are made in a cell by ribosomes, it is messenger RNA (mRNA) that directs protein synthesis.[2][3] The mRNA sequence is determined by the sequence of genomic DNA.[4] In this context, the standard genetic code is referred to as translation table 1.[3] It can also be represented in a DNA codon table. The DNA codons in such tables occur on the sense DNA strand and are arranged in a 5′-to-3′ direction. Different tables with alternate codons are used depending on the source of the genetic code, such as from a cell nucleus, mitochondrion, plastid, or hydrogenosome.[5]

There are 64 different codons in the genetic code and the below tables; most specify an amino acid.[6] Three sequences, UAG, UGA, and UAA, known as stop codons,[note 1] do not code for an amino acid but instead signal the release of the nascent polypeptide from the ribosome.[7] In the standard code, the sequence AUG—read as methionine—can serve as a start codon and, along with sequences such as an initiation factor, initiates translation.[3][8][9] In rare instances, start codons in the standard code may also include GUG or UUG; these codons normally represent valine and leucine, respectively, but as start codons they are translated as methionine or formylmethionine.[3][9]

The first table—the standard table—can be used to translate nucleotide triplets into the corresponding amino acid or appropriate signal if it is a start or stop codon. The second table, appropriately called the inverse, does the opposite: it can be used to deduce a possible triplet code if the amino acid is known. As multiple codons can code for the same amino acid, the International Union of Pure and Applied Chemistry's (IUPAC) nucleic acid notation is given in some instances.

Translation table 1[edit]

Standard RNA codon table[edit]

Amino-acid biochemical properties

Nonpolar

Polar

Basic

Acidic ↓

Termination: stop codon *

Initiation: possible start codon

Standard genetic code[1][10]1st
base 2nd base 3rd
base U C A G UU C A G CU C A G AU C A G GU C A G

UUU	(Phe/F) Phenylalanine	UCU	(Ser/S) Serine	UAU	(Tyr/Y) Tyrosine	UGU	(Cys/C) Cysteine
UUC	UCC	UAC	UGC
UUA	(Leu/L) Leucine	UCA	UAA	Stop (Ochre) *[note 2]	UGA	Stop (Opal) *[note 2]
UUG	UCG	UAG	Stop (Amber) *[note 2]	UGG	(Trp/W) Tryptophan
CUU	CCU	(Pro/P) Proline	CAU	(His/H) Histidine	CGU	(Arg/R) Arginine
CUC	CCC	CAC	CGC
CUA	CCA	CAA	(Gln/Q) Glutamine	CGA
CUG	CCG	CAG	CGG
AUU	(Ile/I) Isoleucine	ACU	(Thr/T) Threonine	AAU	(Asn/N) Asparagine	AGU	(Ser/S) Serine
AUC	ACC	AAC	AGC
AUA	ACA	AAA	(Lys/K) Lysine	AGA	(Arg/R) Arginine
AUG	(Met/M) Methionine	ACG	AAG	AGG
GUU	(Val/V) Valine	GCU	(Ala/A) Alanine	GAU	(Asp/D) Aspartic acid ↓	GGU	(Gly/G) Glycine
GUC	GCC	GAC	GGC
GUA	GCA	GAA	(Glu/E) Glutamic acid ↓	GGA
GUG	GCG	GAG	GGG

Inverse RNA codon table[edit]

Inverse table for the standard genetic code (compressed using IUPAC notation)[13]Amino acidRNA codonsCompressed Amino acidRNA codonsCompressed Ala, A Ile, I Arg, R Leu, L Asn, N Lys, K Asp, D Met, M Asn or Asp, B Phe, F Cys, C Pro, P Gln, Q Ser, S Glu, E Thr, T Gln or Glu, Z Trp, W Gly, G Tyr, Y His, H Val, V START STOP

GCU, GCC, GCA, GCG	GCN	AUU, AUC, AUA	AUH
CGU, CGC, CGA, CGG; AGA, AGG	CGN, AGR; or CGY, MGR	CUU, CUC, CUA, CUG; UUA, UUG	CUN, UUR; or CUY, YUR
AAU, AAC	AAY	AAA, AAG	AAR
GAU, GAC	GAY	AUG
AAU, AAC; GAU, GAC	RAY	UUU, UUC	UUY
UGU, UGC	UGY	CCU, CCC, CCA, CCG	CCN
CAA, CAG	CAR	UCU, UCC, UCA, UCG; AGU, AGC	UCN, AGY
GAA, GAG	GAR	ACU, ACC, ACA, ACG	ACN
CAA, CAG; GAA, GAG	SAR	UGG
GGU, GGC, GGA, GGG	GGN	UAU, UAC	UAY
CAU, CAC	CAY	GUU, GUC, GUA, GUG	GUN
AUG	UAA, UGA, UAG	URA, UAR

Standard DNA codon table[edit]

Amino-acid biochemical properties

Nonpolar

Polar

Basic

Acidic ↓

Termination: stop codon *

Initiation: possible start codon

Standard genetic code[14][note 3]1st
base 2nd base 3rd
base T C A G TT C A G CT C A G AT C A G GT C A G

TTT	(Phe/F) Phenylalanine	TCT	(Ser/S) Serine	TAT	(Tyr/Y) Tyrosine	TGT	(Cys/C) Cysteine
TTC	TCC	TAC	TGC
TTA	(Leu/L) Leucine	TCA	TAA	Stop (Ochre) *[note 2]	TGA	Stop (Opal) *[note 2]
TTG	TCG	TAG	Stop (Amber) *[note 2]	TGG	(Trp/W) Tryptophan
CTT	CCT	(Pro/P) Proline	CAT	(His/H) Histidine	CGT	(Arg/R) Arginine
CTC	CCC	CAC	CGC
CTA	CCA	CAA	(Gln/Q) Glutamine	CGA
CTG	CCG	CAG	CGG
ATT	(Ile/I) Isoleucine	ACT	(Thr/T) Threonine	AAT	(Asn/N) Asparagine	AGT	(Ser/S) Serine
ATC	ACC	AAC	AGC
ATA	ACA	AAA	(Lys/K) Lysine	AGA	(Arg/R) Arginine
ATG	(Met/M) Methionine	ACG	AAG	AGG
GTT	(Val/V) Valine	GCT	(Ala/A) Alanine	GAT	(Asp/D) Aspartic acid ↓	GGT	(Gly/G) Glycine
GTC	GCC	GAC	GGC
GTA	GCA	GAA	(Glu/E) Glutamic acid ↓	GGA
GTG	GCG	GAG	GGG

Inverse DNA codon table[edit]

Inverse table for the standard genetic code (compressed using IUPAC notation)[13]Amino acidDNA codonsCompressed Amino acidDNA codonsCompressed Ala, A Ile, I Arg, R Leu, L Asn, N Lys, K Asp, D Met, M Asn or Asp, B Phe, F Cys, C Pro, P Gln, Q Ser, S Glu, E Thr, T Gln or Glu, Z Trp, W Gly, G Tyr, Y His, H Val, V START STOP

GCT, GCC, GCA, GCG	GCN	ATT, ATC, ATA	ATH
CGT, CGC, CGA, CGG; AGA, AGG	CGN, AGR; or CGY, MGR	CTT, CTC, CTA, CTG; TTA, TTG	CTN, TTR; or CTY, YTR
AAT, AAC	AAY	AAA, AAG	AAR
GAT, GAC	GAY	ATG
AAT, AAC; GAT, GAC	RAY	TTT, TTC	TTY
TGT, TGC	TGY	CCT, CCC, CCA, CCG	CCN
CAA, CAG	CAR	TCT, TCC, TCA, TCG; AGT, AGC	TCN, AGY
GAA, GAG	GAR	ACT, ACC, ACA, ACG	ACN
CAA, CAG; GAA, GAG	SAR	TGG
GGT, GGC, GGA, GGG	GGN	TAT, TAC	TAY
CAT, CAC	CAY	GTT, GTC, GTA, GTG	GTN
ATG	TAA, TGA, TAG	TRA, TAR

Alternative codons in other translation tables[edit]

The genetic code was once believed to be universal:[16] a codon would code for the same amino acid regardless of the organism or source. However, it is now agreed that the genetic code evolves,[17] resulting in discrepancies in how a codon is translated depending on the genetic source.[16][17] For example, in 1981, it was discovered that the use of codons AUA, UGA, AGA and AGG by the coding system in mammalian mitochondria differed from the universal code.[16] Stop codons can also be affected: in ciliated protozoa, the universal stop codons UAA and UAG code for glutamine.[17][note 4] The following table displays these alternative codons.

Amino-acid biochemical properties

Nonpolar

Polar

Basic

Acidic ↓

Termination: stop codon *

Comparison between codon translations with alternative and standard genetic codes[3]Code Translation
table DNA codon involved RNA codon involved Translation
with this code Standard translation Notes StandardVertebrate mitochondrialYeast mitochondrialMold, protozoan, and coelenterate mitochondrial + Mycoplasma / SpiroplasmaInvertebrate mitochondrialCiliate, dasycladacean and Hexamita nuclearEchinoderm and flatworm mitochondrialEuplotid nuclearBacterial, archaeal and plant plastidAlternative yeast nuclearAscidian mitochondrialAlternative flatworm mitochondrialBlepharisma nuclearChlorophycean mitochondrialTrematode mitochondrialScenedesmus obliquus mitochondrialThraustochytrium mitochondrialPterobranchia mitochondrialCandidate division SR1 and GracilibacteriaPachysolen tannophilus nuclearKaryorelict nuclearCondylostoma nuclearMesodinium nuclearPeritrich nuclearBlastocrithidia nuclearCephalodiscidae mitochondrial code

1					Includes translation table 8 (plant chloroplasts).
2	AGA	AGA	Stop *	Arg (R)
AGG	AGG	Stop *	Arg (R)
ATA	AUA	Met (M)	Ile (I)
TGA	UGA	Trp (W)	Stop *
3	ATA	AUA	Met (M)	Ile (I)
CTT	CUU	Thr (T)	Leu (L)
CTC	CUC	Thr (T)	Leu (L)
CTA	CUA	Thr (T)	Leu (L)
CTG	CUG	Thr (T)	Leu (L)
TGA	UGA	Trp (W)	Stop *
CGA	CGA	absent	Arg (R)
CGC	CGC	absent	Arg (R)
4	TGA	UGA	Trp (W)	Stop *	Includes the translation table 7 (kinetoplasts).
5	AGA	AGA	Ser (S)	Arg (R)
AGG	AGG	Ser (S)	Arg (R)
ATA	AUA	Met (M)	Ile (I)
TGA	UGA	Trp (W)	Stop *
6	TAA	UAA	Gln (Q)	Stop *
TAG	UAG	Gln (Q)	Stop *
9	AAA	AAA	Asn (N)	Lys (K)
AGA	AGA	Ser (S)	Arg (R)
AGG	AGG	Ser (S)	Arg (R)
TGA	UGA	Trp (W)	Stop *
10	TGA	UGA	Cys (C)	Stop *
11					See translation table 1.
12	CTG	CUG	Ser (S)	Leu (L)
13	AGA	AGA	Gly (G)	Arg (R)
AGG	AGG	Gly (G)	Arg (R)
ATA	AUA	Met (M)	Ile (I)
TGA	UGA	Trp (W)	Stop *
14	AAA	AAA	Asn (N)	Lys (K)
AGA	AGA	Ser (S)	Arg (R)
AGG	AGG	Ser (S)	Arg (R)
TAA	UAA	Tyr (Y)	Stop *
TGA	UGA	Trp (W)	Stop *
15	TAG	UAG	Gln (Q)	Stop *	As of Nov. 18, 2016: absent from the NCBI update. Similar to translation table 6.
16	TAG	UAG	Leu (L)	Stop *
21	TGA	UGA	Trp (W)	Stop *
ATA	AUA	Met (M)	Ile (I)
AGA	AGA	Ser (S)	Arg (R)
AGG	AGG	Ser (S)	Arg (R)
AAA	AAA	Asn (N)	Lys (K)
22	TCA	UCA	Stop *	Ser (S)
TAG	UAG	Leu (L)	Stop *
23	TTA	UUA	Stop *	Leu (L)	Similar to translation table 11.
24	AGA	AGA	Ser (S)	Arg (R)
AGG	AGG	Lys (K)	Arg (R)
TGA	UGA	Trp (W)	Stop *
25	TGA	UGA	Gly (G)	Stop *
26	CTG	CUG	Ala (A)	Leu (L)
27	TAA	UAA	Gln (Q)	Stop *
TAG	UAG	Gln (Q)	Stop *
TG	UGA	Stop *	or	Trp (W)	Stop *
28	TAA	UAA	Stop *	or	Gln (Q)	Stop *
TAG	UAG	Stop *	or	Gln (Q)	Stop *
TGA	UGA	Stop *	or	Trp (W)	Stop *
29	TAA	UAA	Tyr (Y)	Stop *
TAG	UAG	Tyr (Y)	Stop *
30	TA	UAA	Glu (E) ↓	Stop *
TAG	UAG	Glu (E) ↓	Stop *
31	TAA	UAA	Stop *	or	Glu (E) ↓	Stop *
TAG	UAG	Stop *	or	Glu (E) ↓	Stop *
TGA	UGA	Trp (W)	Stop *
33	AGA	AGA	Ser (S)	Arg (R)	Similar to translation table 24.
AGG	AGG	Lys (K)	Arg (R)
TAA	UAA	Tyr (Y)	Stop *
TGA	UGA	Trp (W)	Stop *

See also[edit]

• Bioinformatics
• List of genetic codes

Notes[edit]

1. ^ Each stop codon has a specific name: UAG is amber, UGA is opal or umber, and UAA is ochre.[7] In DNA, these stop codons are TAG, TGA, and TAA, respectively.
2. ^ a b c d e f The historical basis for designating the stop codons as amber, ochre and opal is described in the autobiography of Sydney Brenner[11] and in a historical article by Bob Edgar.[12]
3. ^ The major difference between DNA and RNA is that thymine (T) is only found in the former. In RNA, it is replaced with uracil (U).[15] This is the only difference between the standard RNA codon table and the standard DNA codon table.
4. ^ Euplotes octacarinatus is an exception.[17]

References[edit]

1. ^ a b "Amino Acid Translation Table". Oregon State University. Archived from the original on 29 May 2020. Retrieved 2 December 2020.
2. ^ a b Bartee, Lisa; Brook, Jack. MHCC Biology 112: Biology for Health Professions. Open Oregon. p. 42. Archived from the original on 6 December 2020. Retrieved 6 December 2020.
3. ^ a b c d e Elzanowski A, Ostell J (7 January 2019). "The Genetic Codes". National Center for Biotechnology Information. Archived from the original on 9 October 2020. Retrieved 21 February 2019.
4. ^ "RNA Functions". Scitable. Nature Education. Archived from the original on 18 October 2008. Retrieved 5 January 2021.
5. ^ "The Genetic Codes". National Center for Biotechnology Information. Archived from the original on 13 May 2011. Retrieved 2 December 2020.
6. ^ "Codon". National Human Genome Research Institute. Archived from the original on 22 October 2020. Retrieved 10 October 2020.
7. ^ a b Maloy S. (29 November 2003). "How nonsense mutations got their names". Microbial Genetics Course. San Diego State University. Archived from the original on 23 September 2020. Retrieved 10 October 2020.
8. ^ Hinnebusch AG (2011). "Molecular Mechanism of Scanning and Start Codon Selection in Eukaryotes". Microbiology and Molecular Biology Reviews. 75 (3): 434–467. doi:10.1128/MMBR.00008-11. PMC 3165540. PMID 21885680.
9. ^ a b Touriol C, Bornes S, Bonnal S, Audigier S, Prats H, Prats AC, Vagner S (2003). "Generation of protein isoform diversity by alternative initiation of translation at non-AUG codons". Biology of the Cell. 95 (3–4): 169–78. doi:10.1016/S0248-4900(03)00033-9. PMID 12867081.
10. ^ "The Information in DNA Determines Cellular Function via Translation". Scitable. Nature Education. Archived from the original on 23 September 2017. Retrieved 5 December 2020.
11. ^ Brenner, Sydney; Wolpert, Lewis (2001). A Life in Science. Biomed Central Limited. pp. 101–104. ISBN 9780954027803.
12. ^ Edgar B (2004). "The genome of bacteriophage T4: an archeological dig". Genetics. 168 (2): 575–82. doi:10.1093/genetics/168.2.575. PMC 1448817. PMID 15514035. see pages 580–581
13. ^ a b IUPAC—IUB Commission on Biochemical Nomenclature. "Abbreviations and Symbols for Nucleic Acids, Polynucleotides and Their Constituents" (PDF). International Union of Pure and Applied Chemistry. Retrieved 5 December 2020.
14. ^ "What does DNA do?". Your Genome. Welcome Genome Campus. Archived from the original on 29 November 2020. Retrieved 12 January 2021.
15. ^ "Genes". DNA, Genetics, and Evolution. Boston University. Archived from the original on 28 April 2020. Retrieved 10 December 2020.
16. ^ a b c Osawa, A (November 1993). "Evolutionary changes in the genetic code". Comparative Biochemistry and Physiology. 106 (2): 489–94. doi:10.1016/0305-0491(93)90122-l. PMID 8281749.
17. ^ a b c d Osawa S, Jukes TH, Watanabe K, Muto A (March 1992). "Recent evidence for evolution of the genetic code". Microbiological Reviews. 56 (1): 229–64. doi:10.1128/MR.56.1.229-264.1992. PMC 372862. PMID 1579111.

Further reading[edit]

• Chevance FV, Hughes KT (2 May 2017). "Case for the genetic code as a triplet of triplets". Proceedings of the National Academy of Sciences of the United States of America. 114 (18): 4745–4750. doi:10.1073/pnas.1614896114. JSTOR 26481868. PMC 5422812. PMID 28416671.
• Dever TE (29 June 2012). "A New Start for Protein Synthesis". Science. American Association for the Advancement of Science. 336 (6089): 1645–1646. Bibcode:2012Sci...336.1645D. doi:10.1126/science.1224439. JSTOR 41585146. PMID 22745408. S2CID 44326947. Retrieved 17 October 2020.
• Gardner RS, Wahba AJ, Basilio C, Miller RS, Lengyel P, Speyer JF (December 1962). "Synthetic polynucleotides and the amino acid code. VII". Proceedings of the National Academy of Sciences of the United States of America. 48 (12): 2087–2094. Bibcode:1962PNAS...48.2087G. doi:10.1073/pnas.48.12.2087. PMC 221128. PMID 13946552.
• Nakamoto T (March 2009). "Evolution and the universality of the mechanism of initiation of protein synthesis". Gene. 432 (1–2): 1–6. doi:10.1016/j.gene.2008.11.001. PMID 19056476.
• Wahba AJ, Gardner RS, Basilio C, Miller RS, Speyer JF, Lengyel P (January 1963). "Synthetic polynucleotides and the amino acid code. VIII". Proceedings of the National Academy of Sciences of the United States of America. 49 (1): 116–122. Bibcode:1963PNAS...49..116W. doi:10.1073/pnas.49.1.116. PMC 300638. PMID 13998282.
• Yanofsky C (9 March 2007). "Establishing the Triplet Nature of the Genetic Code". Cell. 128 (5): 815–818. doi:10.1016/j.cell.2007.02.029. PMID 17350564. S2CID 14249277.
• Zaneveld J, Hamady M, Sueoka N, Knight R (28 February 2009). "CodonExplorer: An Interactive Online Database for the Analysis of Codon Usage and Sequence Composition". Bioinformatics for DNA Sequence Analysis. Methods in Molecular Biology. Vol. 537. pp. 207–232. doi:10.1007/978-1-59745-251-9_10. ISBN 978-1-58829-910-9. PMC 2953947. PMID 19378146.

External links[edit]

• DNA codon chart organized in a wheel

Which nucleotides sequence code for an amino acid?

What is an amino acid sequence called?

What is a sequence of nucleotides that codes for a protein?

What are 3 bases that code for an amino acid called?