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Hello all,
I've been trying to figure this question out for a week now, but can't seem to be reaching a logical answer.
I'd very much appreciate if anyone could help me see how this prolem should be solved.
Here it goes:

Consider the following wild-type amino acid sequence in bacteria:

A researcher has induced various mutations in the bacteria, and has isolated two species containing a mutant amino acid sequence.
Sequence #2:

Sequence #3:

1. State the Sense-DNA sequence for each of the above amino-acid sequences.
2. What Amino Acid could be "X" in sequence #3? State all possible answers.

Thanks A lot!!!


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Could you explain what you have tried so far?

What do they mean with sense-DNA sequence you think?

Have you looked at sequences that code for these amino acids? I think you have to go and look at what happened to the sequence, maybe you can see which type of mutation happened (maybe name the types of mutations that exist).

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I'd say what I'm struggling with the most is figuring out what X could stand for.
The mutations in Sequence #2 are simple substitution mutations coding for tyr and met.
In sequence #3 there must be 3 insertion mutations that will cause an addition of an extra codon, coding for an additional amino acid.
But there could be so many possibilities and I can't find a simple way to answer this question, not stating around 100 options. 
The Sense DNA strand is the DNA Strand who's nucleotide sequence corresponds directly to the sequence of an RNA transcript which is translated.

The sense DNA for sequence 3 would be:
So i'm assuming there were 3 insertion mutations, roundabout phe-lys.
But again, it could be anything and there are many possibilities. 
Is there any smart way to get around this?

– Lys –

– Phe –

– Ile –

– Leu –

– Cys –

Amino Acid Sequence







RNA Sequence

– AAA –

– TTT–

– ATT –

– TTA –

– TGT –

Sense DNA Sequence

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Posted (edited)

Ahh at further inspection I spot my own mistake, I thought both sequences had the same amount of amino acids, and thus thought that in sequence 3 we would be looking at a frameshift mutation that would then mean we could puzzle our way through... Hmm I'll think of it, but with that extra amino acid it basically means anything goes (or well, I currently can't think of anything). 

Edit: the jump from serine to lys is also pretty strange if it would be a substitution reaction. I don't feel like going through it completely (so this is not per sé an answer, but a thing to explore), but I think an insertion at phe (sequence 3, position 4) could maybe be the answer, thereby leading to a frameshift and an additional amino acid. So knowing that the stop codons are UAA, UAG, and UGA. How would we go from Leu (position 4) to phe (position 4 in sequence 3). Leu = TTA, TTG, CTT, CTC, CTA, CTG. to phe (TTT, TTC) so that the the third nucleotide of what previously was Leu can combine together with Ser (TCT TCC TCA TCG AGT AGC) and the old stop codon (UAA, UAG, UGA) to form Lys (AAA AAG) and a new stop codon (UAA, UAG, UGA). This way X should (if this is the answer) not be too many different possible combinations.

I am not sure if this will give you the answer, but its the only thing I can think of at the moment.

Oh and of course assuming a simple substitution mutation for position 1. It may be also at the beginning, but that would make it even more complicated

Edited by Dagl1

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