Problem : The following three bases specify for the amino acid cysteine. Label the 5' and 3' ends of the sequence:


If we refer to we can find all the codon sequences that code for cysteine. There are only two codons that specify for cysteine. They are 5'-UGU-3' and 5'-UGC-3'. The second possibility matches our codon if we label it in the following manner 3'-CGU-5'.

Problem : List the three amino acid sequences that could result from the following base sequence:

5'-A U A G C A G G A C U U-3'

There are three possible reading frames for this sequence because we must read it in the 5' to 3' direction. If we start with the first base and read by threes we get: AUA, GCA, GGA, and CUU. Refering to , we see that this sequence codes for the amino acids 5'- isoleucine-alanine- glycine-leucine – 3'. If we start with the second base from the 5' end and read in threes, we get: UAG, CAG, GAC. The first codon codes for a stop codon, the second for glutamine, and the third for aspartate. If we begin at the third base from the 5' end, we get: AGC, AGG, ACU. This sequence codes for the amino acids 5'-serine-arginine-threonine-3'.

Problem : Identify the codon that would be the first codon translated into a protein during translation in the following sequence:

5'-A C G U A G G U C A U G C C G C G U A C G G G-3'

The first codon is always an AUG or GUG.
5'-A C G U A G G U C A U G C C G C G U A C G G G-3'