Molecular Biology

[pharm357]

In the absence of Uracil DNA Glycosylase (a mutant) you would expect

1. More transition mutations than transversion mutations
2. More transversion mutations than transition mutations
3. the same number of transition and transversion mutations
4. No mutation
5. Less mutation than in the presence of a Uracil DNA Glycosylase

Any one interested in explaining this question for me is apperciated

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[El Trombopag]

I'd guess 2. The lack of UDG should mean fewer template corrections of uracil back to cytosine. That means subsequent replication events will produce adenosine from those uracils -- effecting a template change from C to A (on half the progeny strands anyway). Pyrimidine to purine changes are transversions, thus #2 seems to be what they're going for.

 

[LatePrePharm]

I think it's number 2 as well.

For instance, say we start off with the strand 5'-CCCC-3'. We want to make the complementary strand to this, which would be 5'-GGGG-3', but we end up making 5'-GUGG-3' on accident. Normally uracil DNA glycosylase would remove the U so we can replace it with a G like it's supposed to be, but it's mutated so that doesn't happen. From that 5'-GUGG-3' we accidently made, we make the complementary strand 5'-CCAC-3', which goes to make 5'-GUGG-3', which goes to make 5'-CCAC-3', etc etc.

So we changed the original sequence 5'-CCCC-3' to 5'-CCAC-3' in the daughter cells. A switch from a pyrimidine (C) to a purine (A), or vice-versa, is called transversion.