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Appendix 1: Codon Table

  • Page ID
    73681
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    Codon Table

    Second Position

    U

    C

    A

    G

    code

    amino acid

    code

    amino acid

    code

    amino acid

    code

    amino acid

    First Position

    U

    UUU

    phe

    UCU

    ser

    UAU

    tyr

    UGU

    cys

    U

    Third Position

    UUC

    UCC

    UAC

    UGC

    C

    UUC

    leu

    UCA

    UAA

    STOP

    UGA

    STOP

    A

    UUG

    UCG

    UAG

    STOP

    UGG

    trp

    G

    C

    CUU

    leu

    CCU

    pro

    CAU

    his

    CGU

    arg

    U

    CUC

    CCC

    CAC

    CGC

    C

    CUA

    CCA

    CAA

    gln

    CGA

    A

    CUG

    CCG

    CAG

    CGG

    G

    A

    AUU

    ile

    ACU

    thr

    AAU

    asn

    AGU

    ser

    U

    AUC

    ACC

    AAC

    AGC

    C

    AUA

    ACA

    AAA

    lys

    AGA

    arg

    A

    AUG

    met START

    ACG

    AAG

    AGG

    G

    G

    GUU

    val

    GCU

    ala

    GAU

    asp

    GGU

    gly

    U

    GUC

    GCC

    GAC

    GGC

    C

    GUA

    GCA

    GAA

    glu

    GGA

    A

    GUG

    GCG

    GAG

    GGG

    G

    Each three-letter sequence of mRNA nucleotides corresponds to a specific amino acid, or to a stop codon. UGA, UAA, and UAG are stop codons. AUG is the codon for methionine, and is also the start codon.

    To see how the codon table works, let’s walk through an example. Suppose that we are interested in the codon CAG and want to know which amino acid it specifies.

    1. First, we look at the left side of the table. The axis on the left side refers to the first letter of the codon, so we find C along the left axis. This tells us the (broad) row of the table in which our codon will be found.
    2. Next, we look at the top of the table. The upper axis refers to the second letter of the codon, so we find A along the upper axis. This tells us the column of the table in which our codon will be found.

    The row and column from steps 1 and 2 intersect in a set of boxes in the codon table, one half containing four codons and the other half containing the mapped amino acid(s). It’s often easiest to simply look at these four codons and see which one is the one you’re looking for.

    If you want to use the structure of the table to the maximum, however, you can use the third axis (on the right side of the table) corresponding to the intersect box. By finding the third nucleotide of the codon on this axis, you can identify the exact row within the box where your codon is found. For instance, if we look for G on this axis in our example above, we find that CAG encodes the amino acid glutamine (gln).[1]


    1. This description of a codon table is from "The genetic code" on Khan Academy, available under a Creative Commons Attribution NonCommercial ShareAlike 4.0 License
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