In order for DNA (deoxyribonucleic acid) to be used in the cell, it must be converted into RNA (ribonucleic acid). The conversion of DNA into RNA is called transcription.
DNA is a double-stranded molecule that consists of a primary coding strand and a complementary strand. To transcribe DNA into RNA, the coding strand of DNA (made of molecules called nucleotides) has a complementary strand of RNA formed from it, where uracil is placed wherever thymine would have been.
With complimentary DNA, the nucleotide (A) Adenine pairs with (T) Thymine and (C) Cytosine pairs with (G) Guanine
If the DNA strand read:
TAC TGC CTC GAA GCC TCG ATC
The complimentary RNA strand produced during transcription (replacing uracil with thymine) would be:
AUG ACG GAG CUU CGG AGC UAG