Question

3’ - TAC AAA GAG GAT CCG ACC TCA ACT - 5”

3. The DNA template for transcription is only one strand of the DNA double helix. How do we know that the mRNA is not based on the sequence of the other DNA strand?

4. What is the anticodon sequence of the tRNA that binds to the fourth codon of this mRNA?

5. Translate the mRNA sequence into the amino acid sequence (use the genetic code table from the lecture slides).

6. How many amino acids does this protein have?

7. Can we tell if this protein was synthesized in a bacterial cell versus eukaryotic cell?

Answer 1

3' – TAC AAA GAG GAT CCG ACC TCA ACT – 5'

3. The RNA polymerase enzyme synthesize mRNA in 5'→3' direction. So, the DNA starnd which acts as the template strand for that particular mRNA must have 3' end at beginning, and a complementary codon triplet for a start codon of transcription near the 3' end where the RNA polymerase will bind and start synthesizing mRNA. Analysing the above strand we can clearly note that near the 3' end there's a codon triplet TAC which is the complementary to start codon AUG. So, we can conclude that the mRNA is based on the sequence of above strand.

4. The mRNA transcribed from the above DNA strand will be as following :

5' – AUG UUU CUC GGC UGG AGU UGA – 3'

So, the anticodon sequence of the tRNA that will bind to the fourth codon of this mRNA is CCG

5. The amino acid sequence after translation from this mRNA sequence will be as following :

Met (Start) – Phe – Leu – Gly – Trp – Ser – (Stop)

*AUG is the start codon which codes for methionine and UGA is the stop codon where the translation stops.

6. The protein have six amino acids : Met (Methionine), Phe (Phenylalanine), Leu (Leucine), Gly (Glycine), Trp (Tryptophan) and Ser (Serine).

7. It is diffuct to tell if the protein was synthesized in a bacterial cell or an eukaryotic cell. Some indea can be achieved by the help of information regarding codon bias. Codon bias is the phenomenon that narrates many amnio acids can be encoded by more than one codon. Different species of eukaryotes and prokaryotes follow different codon to encode same amnio acid. In this way the start and stop codon may also vary in eukaryotes and prokaryotes. While eukaryotic translation generally starts with the AUG codon, prokaryotic translation permits frequent GUG and UUG initiation besides AUG.

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