Understand the base pairing rules that are associated with DNA. The bases of DNA are adenine, thymine, cytosine and guanine. They are often shortened to A, T, C and G in charts. The purines are adenine and guanine, and the pyrimidines are cytosine and thymine. Adenine pairs with thymine, and cytosine pairs with guanine. Therefore, the amounts of adenine and thymine are equal. The amounts of cytosine and guanine are equal.
Fill in the bases for the complementary DNA strand. In a DNA decoding chart problem, you will usually be given the bases of a single strand of DNA. For example, the bases may be
ACCTGCACA. Based on the base pairing rules, the base pairs for the complementary strand are TGGACGTGT.
Know which bases are present in RNA. RNA and DNA both have adenine, cytosine and guanine. However, RNA does not have the base thymine. Instead, RNA has uracil, or U. In RNA, the uracil pairs with adenine, and the cytosine pairs with the guanine.
Fill in the bases for the messenger RNA strand. For example, if the complementary DNA strand is TGGACGTGT, then the messenger RNA strand is ACCUGCACA.
Divide the bases of the messenger RNA strands into codons of three base pairs. For example, the codons of ACCUGCACA are ACC, UGC, and ACA.
Determine which amino acid the codons code for. The three letters of the messenger RNA, the codon, correspond to the amino acid that will be produced. If the messenger RNA codon is UCA, you find UCA on the chart, and the amino acid above it is serine, Ser. This means that the codon of uracil, cytosine and adenine codes for, or leads to, the production of serine. You will be provided with a sheet that gives the codons that correspond to each of the amino acids. Such a chart can also be found online and in a biology book. For example, ACC codes for threonine, or Thr. UGC codes for cysteine, or Cys. The codon ACA codes for threonine, or Thr.