Question

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Question Completion Status: Question 10: The genetic code consists of 64 triplets of nucleotides (called codons). Each codon (with the exception of the 3 stop codons) encodes for one of the 20 amino acids used in the synthesis of proteins. This produces some redundancy in the code as most amino acids are encoded by more than one codon. One codon, AUG serves two related functions: it signals the start of translation and it codes for the incorporation of the amino acid met hionine (Met) into the growing polypeptide chain. Note that in the genetic code table (shown below), the left-hand column gives the first nucleotide of the mRNA codon (called the 'first letter'), the 4 middle columns give the second nucleotide of mRNA codon (called the 'second letter'), and the last column gives the third nucleotide of the mRNA codon (called the 'third letter). The codons in the genetic code table are always given in the 5' to 3' direction. An mRNA codon has the sequence: 5' AAG 3'. What amino acid does it encode for? (Use the drop-down menu to make your selection; in this menu, each amino acid is given both by its full name and 3-letter abbreviation). The amino acid encoded by the mRNA codon 5' AAG 3' is 4. (1 mark) You will need to consult the genetic code to answer this question. Here is the genetic code table (you can also consult Figure 11.5 in your textbook): Second letter с Т А Huu Hawa

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Answer 1

In order to determine the amino acid for a given genetic code, we can do so using the codon table. As you can see that the codon table has three outer regions in blue, marked as First letter, Second letter and Third letter.

Now, the codon sequence given is 5'- AAG -3'.

In this codon, the First letter is A, Second letter is A and the Thrird letter is G.

We need to locate the AAG codon in the table and it will show which amino acid it codes for.

If you look at the codon table keenly enough, you would notice that the column to the left labeled "First letter" has 4 rows for each of the four nucleotides, UCAG.

That which is labeled "Second letter" has four columns for the 4 nucleotides, and for the third letter, there are 4 rows each within each of the 4 rows assigned for the first letter.

Now, the first step would be to find the first letter and fix that particular row. The first letter in AAG is A and so we need to look for the codon in the third row of the 'first letter' (red box)  .

Next, we locate the second letter which is again "A" . Now we need to look at the third column under "second letter" and focus on the box (marked in blue) where the third column meets the third row of the first letter.

Finally, we look at the third letter G in the same blue box and find that the AAG codon (green) codes for the amino acid Lysine (where it says Lys).

The amino acid encoded by the mRNA codon "5'- AAG -3' is Lysine (Lys).

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