This question is asking us to get from the template strand of a DNA molecule to the protein sequence. The process of transcription involves turning DNA into mRNA, and then translation involves turning that mRNA into a protein using tRNA molecules.
To understand this question fully, it's important to first go over key terms first:
Template Strand: This is the DNA sequence that will be complementary to the mRNA strand that is generated. To do this, we want to write the complementary base pairs (A -> U, T -> A, C -> G, and G-> C). DNA contains T nucleotides while RNA does not, so you want to make sure you base pair A with U instead in your mRNA!
mRNA: Messenger mRNA sequence. mRNA is a molecule that ribosomes can read and generate the corresponding protein that is coded for by the mRNA.
Anticodon: A complementary section of a tRNA molecule to the mRNA molecule. These consist of 3 base pairs that complementarily bind to the codons (3 base pair segments) of the RNA that code for tRNAs.
To start, I recommend writing out your template strand sequence with some space above with the annotated directions to create your mRNA sequence like this:
mRNA. : 5' - AUGAAGCCAUGUGGGUAG - 3'
Template DNA : 3' - TACTTCGGTACACCCATC - 5'
(Remember to always annotate the directions of your strands when you write out the sequence. mRNA is always read in the 5' to 3' direction by ribosomes and is made by converting your DNA sequence in the 3' to 5' direction. RNA and DNA are always antiparallel, meaning that, in order to bind, one strand has to be going 5' to 3' and the other strand has to be going 3' to 5'.)
To double-check how we did this, I often recommend students look for several things. First, your mRNA molecule should start with the universal start codon (AUG). This sequence brings in the tRNA molecule that will initiate translation (fMet). Since we see that in this sequence, that's a good sign that you generated the correct complementary mRNA sequence. We also see "UAG" at the end of the sequence, which is a universal stop codon. Every mRNA that is translated into a protein needs both a start and stop codon, so our transcription of the DNA looks good so far!
Now that we have the mRNA sequence, we can use the genetic code to decipher which amino acids correspond with which portions of the mRNA molecule. The genetic code is read in 3 base pair segments, meaning that there is an amino acid encoded by each 3 base pairs. So let's divide our RNA sequence into 3 base pair segments:
AUG
AAG
CCA
UGU
GGG
UAG
Now, let's see what the corresponding anticodon for the tRNAs have to be. In order to bind to the mRNA molecule, these anticodons have to be complementary (A-U, U-A, G-C, C-G) to what we wrote above:
AUG | UAC
AAG | UUC
CCA | GGU
UGU | ACA
GGG | CCC
UAG | AUC
Interestingly, you'll notice that these anticodons end up being almost identical to the starting template DNA due to them also being complementary to the mRNA! However, we use "U" instead of "T" as T is a base that is only found in DNA sequences.
Finally, let's figure out which amino acid corresponds to the tRNA we wrote. Frequently, you'll see genetic codes that are based on the mRNA sequence, and you can also use that to solve for the sequence of the protein rather than the anticodons we just placed. I'll add a third column that uses the genetic code to solve for the identity of the proteins. These are usually in charts or tables you can find online.
AUG | UAC | N-formyl Methionine
AAG | UUC | Phenylalanine
CCA | GGU | Glycine
UGU | ACA | Threonine
GGG | CCC | Proline
UAG | AUC | Stop Codon
And there you have your full protein sequence! As we note here, you see your starting amino acid (fMet) which should always be the first amino acid in a protein sequence. Then, we finish the sequence with a stop codon, meaning that we've completed the full protein translation!
Hope this helps!
