1. DNA remains in the nucleus of the cell where it is "safe." mRNA will come in and create a complementary copy of the DNA and can/ will move outside the nucleus into the cell. This is then read by tRNA to create an exact copy of the DNA in order to form a string of amino acids.
2. The trinucleotide structure of DNA consists of A, T,G and C. In RNA the T is replaced with a U.