2. Now we are going to investigate what happens when a mutation occurs in your D

Question

2. Now we are going to investigate what happens when a mutation occurs in your DNA. Below I have copied the same DNA that you used on the first page of this homework. In problem 1 you already figured out the sequence of amino acids that this DNA codes for. Normal DNA: 3 - ACAGCGCGCGCCTATACTCUS GGGATGCCCTATATAATCAAATGCGGGCCGC-5 Let's assume that a base pair substitution mutation occurs at all of the circled mutations. So, the first A T base pair circled in the normal DNA (above) gets replaced by a G-C base pair at point 1 in the mutated DNA (below). Similarly, the C-G base pair circled in the normal DNA, gets replaced by G-C base pair at point 2 below. Mutated DNA: 5'-TGTCGCGCGCGGATATGAG CCTAGGGGATATATTAGTTTACGCCCGGCG-3 Follow the same procedure you used on the first page of this homework to determine the sequence of amino acids that the mutated DNA codes for (use the same promoter, terminator and introns as on the previous page). After determining the sequence of amino acids, answer the following question: Will each mutation result in a silent, missense, nonsense or frameshift mutation? Explain your answer Mutation 1: Mutation 2:

Explanation / Answer

In this case, the 3' to 5' strand shall serve as the template for the synthesis of the new strand. Thus the orientation of the newly synthesised DNA will be 5' to 3'. This 5' to 3' starnd shall serve for transcription into mRNA and thereby its translation into protein. Thus, we will be scrutinizing the 5' to 3' strand for the type of mutation by decoding the protein sequence.

Since A gets mutated to G ; it can be called as purine- purine transition.And when C gets mutated to G,pyrimidine gets changed to purine;hence it is a tranversion.

On analysing the protein sequence:

Mutation 1: the first mutation engulfs the codon GAC which actually codes for Asp (Aspartic Acid). Here, the A gets mutated to G, and then the codon changes from GAC to GGC. This GGC codes for Gly (Glycine). This is an example of point mutation wherein only a single base changes, thsu changing the amino acid sequence.

Mutation 2: the second mutation engulfs the codon UAC (in case of RNA strand, T is replaced by U) which actually codes for Tyr (Tyrosine). Here, the C gets mutated to G, and then the codon changes from UAC to UAG. This UAG codes for a stop codon. The presence of stop codon halts the process of translation. Hence this mutation is an example of nonsense mutation.

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