MRNA stands for messenger ribonucleic acid; it is a type of RNA you transcribe from a template of DNA. Nature encodes an organism's genetic information into the mRNA. A strand of mRNA consists of four types of bases -- adenine, guanine, cytosine and uracil. Each base corresponds to a complementary base on an antisense strand of DNA.
Determine the order of the bases present in the DNA sequence. Each base has a base pair on the strand opposite it. The four bases are A for adenine, C for cytosine, G for guanine and T for thymine.
Find the antisense strand of DNA by inserting the complementary base pair for each base given. Adenine complements thymine, and cytosine complements guanine. For example, every time you see a C, replace it with a G, and every time you have a G, replace it with a C. The result is the completed antisense DNA helix, or strand.
Find the mRNA base pairs by inserting the RNA bases that correspond to the bases on the antisense DNA helix you found in Step 2. Guanine and cytosine are still complements, but, as Anthony Carpi of John Jay College of New York explains, because the sugar units in RNA are ribose as compared to DNA's deoxyribose, RNA does not bind to the nucleotide base thymine. Instead, the complement of adenine is uracil.
Here's an example of this process. A DNA strand is first, followed by an antisense DNA strand and lastly an mRNA strand.