Insertion/Deletion of bases in DNA sequence

[Louey]

I'm in a quandry with a DNA sequence. I have a polypeptide that starts with the MET codon and am putting a T on the front - which in effect makes the beginning codon Thymine - and then if I start reading the codons from the Thymine it changes the whole polypeptide's sequence (resulting in there being no methionine amino acid) so does this make the polypeptide a mutant or something else? Or do I "ignore" the T as 3 of the bases still give me the MET and as Met is the codon for initiating the translation of the polypeptide?

 

Then back to the original sequence (starting with methionine again) and have to take out the 10th base,

 

my original sequence is AUG UUU GCU GGG GGA, taking out the 10th base gives me AUG UUU GCU GGG GAC, so the 5th amino acid is Asp instead of Gly I'm not sure what the possible final effect on the polypeptide would be!

 

TIA for any enlightenment, this one is driving me nuts and I think I maybe looking for something a bit more complex than what it is (can't see the wood for the trees kind of thing!)

 

Lou

[admiral_ju00]

What are you comparing it with or against?

[Louey]

AUG UUU GCU GGG GGA CAU UCG UGG GCA

 

is the sequence before the addition of the T at the front/deletion of the 10th base

[LucidDreamer]

With the addition of the T to the begining of the sequence you have created a frameshift mutation. This is usually very distructive and usually results in a very abmormal protein because all of the codons after the insertion/deletion are incorrect.(unless the alteration just happens to code for the same amino acid). I did not check to see how many of the codons changed to another amino acid but the amount changed is the key to how much damage is done.

 

On the second part you have created another frameshift mutation by deleting the 10th base. However a frameshift mutation only effects the codons after the insertion/deletion so since the DNA sequence you are looking at is only 5 aminos long and the deletion only affects the 5th codon the effect is not as bad as if it occurred earlier in the sequence. Just how much this insertion effects the function of the sequence depends on many factors. Sometimes by changing one amino acid in a protein sequence you get no change at all and sometimes it totally changes it. It depends on where it is and the function of that amino for the peptide.

 

In this case you have changed from glycine, a polar amino acid, to Aspartic acid, an acidic amino acid. I don't know offhand what this would do but it could be a significant change.

[Louey]

You're a star, thank you that is such a great help, I got the mutation bit but wasn't picking up how the frameshift mutation works and it's knock on effect on the other codons.