GUC AGG AAA CCC
The dna is the script from which mRNA transcribes the message (for a protein). The mRNA creates a complementary string of nucleotides (So where there is a C the mRNA would put a G) except that mRNA uses U instead of T.
The mRNA then takes it to the cytoplasm, where it connects to a ribosome. tRNA go to the ribosome with an attached amino acid. Each tRNA has a codon that is complementary to a 3 letter set of mRNA (Since its complementary the G would be a C).
SO you can basically determine the tRNA when given the dna by simply replacing the T with U.
2.
A change in the nitrogen base will cause a different tRNA to match with the mRNA. (Each tRNA with its codon has a specific amino acid that it brings to the site of translation) This will change the protein because it will be made from a different chain than the original protein.
3.
No. There are repeats, more than one amino acid can be translated from a codon. There are about 22 standard amino acids while there are numerous different codons.
4.
You should be able to piece this together from my earlier explaination
