The start codon (AUG) is on the 5' end of all mRNAs. Each codon attaches to a particular tRNA. 3' end is free and has a base sequence of CCA. There are complimentary bases in tRNA and hydrogen bonds form in four areas. Causes the tRNA to fold and take on a 3 dimensional structure. If it's 2 dimensional shaped, one of the loops contains an exposed anticodon. This specific anticodon pairs with a specific anticodon of mRNA. 20 amino acids, 20 enzymes. ATP energy. Activated amino acid. tRNA delivers amino acid to ribosome to produce polypeptide chain.