Question 32

[kazuma]

32. All of the following are possible results of a point mutation in a strand of DNA which codes for a protein EXCEPT:

1. an amino acid substitution in the corresponding protein. [x]
2. incomplete synthesis of corresponding protein. [x]
3. synthesis of a completely different protein. [x]
4. the substitution of an adenine base for a uracil base. [x]


I understand this question, but I had a question about answer choice 3. Is it possible for a point mutation to cause the synthesis of a completely different protein?

at the most I thought point mutations could change a single nucleotide could result in missense or nonsense mutation. missense a new amino acid and in the case of nonsense a smaller protein (due to premature stop codon). But my assumption was that only indels (insertions/deletions) where the only types of mutations that could create a completely different protein by causing a shift in the reading frame.

[admin]

To properly answer your question is to apply advance level genetics which is not part of the MCAT. If you are trying to differentiate between nonsense and missense mutations then you have forgotten that you are just trying to ace the MCAT which is based on first year biology facts such as uracil is found in RNA and not DNA.

Is it POSSIBLE that a new protein will be created? Well, yes, but very, very unlikely. However, there is a clear best answer.

Try your best to look for simple explanations. There will be a handful of more difficult problems but that is not what will prevent you from acing the MCAT. The real challenge is to make sure that you get everything that you know, based on introductory level sciences, correct.

[kazuma]

thx, I have only taken intro bio courses =[, but i have a tendency to over-read, and over-look up things online and in texts (i do it even for my classes), hopefully it wont hurt me

[quadalpha]

[GraemeMatt8033]

I think what he was trying to say is that all the other options are possible, but its not likely that DNA polymerase will recognize, pick up and incorporate uracil into a DNA strand

[andrewtfai3609]

I think the explanation for this question is flawed. To state the uracil cannot appear in DNA just because it is only supposed to appear in RNA is flawed; for example, uracil can appear in DNA as a result of spontaneous deamination. However, that mechanism doesn't involve (atleast I don't think) adenine; it involves changing cytosine.

Was this question specifically meant to show that adenine cannot change into uracil, or that DNA can never contain uracil?