A single strand of DNA is is described as being of a positive + sense, there are two strands which complement each other, the strand which is used for replication and translation is called the antisense strand( also the watson strand )the sense strand(the crick strand) is the exact opposite. the RNA and mRNA ( stored in the nucleic mitochondrion )are used for protein synthesis. the mRNA is complementary to the DNA antisense stand.the whole idea was just to differentiate between them. one was the sense strand, the other was the antisense, the scientists just had to agree which was which