Biology question?

Question

How would a deletion of one nucleotide in the middle of an mRNA transcript affect the polypeptide specified by that transcript?

Answer 1

You would have what takes the name of a frame-shift mutation. That is, the slippage of one or two nucleotides from the original sequence, which is likely to change the rest of the sequence from the mutation on.

To understand, try to imagine a sentence made of words of 3 letters each :

one cut for any use STOP
(not much sense, it is just an example!)

Now take away a letter in the middle of the sentence (e.g. the t in cut) and make 3-letter words with what is left:

one cuf ora nyu se...
The whole meaning after the t is lost....

Often, these types of mutations lead to premature STOP codons and the expression of truncated forms of the protein (which are normally inactive).

Answer 2

It would cause what is called a 'frame shift' from that point on. What is interesting is that this frequently leads to a stop codon very quickly. So the polypeptide formed would be 'normal' up until the deletion, then have different amino acids, but also likely be shorter than the original protein was supposed to be.

Answer 3

Every amino acid from the point of the deletion on to the end of the chain has the possibility of being wrong.

Note that some changes in mRNA would not change the particular amino acid because some amino acids are called for by more than one mRNA codon.