Mutations - Frameshift, BP, Nonsense...

[sugarbabee0]

On what level do mutations (such as BP deletion/insertion, frame shift, nonsense, and so on) occur? Is it on the DNA or RNA? And when does the mutation occur (during replication/transcription or after)? Why doesn't the exonuclease actvity correct it?

I know thats a lot of questions at once but just realized how little I know about these mutations...

Thanks

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[vsl5]

DNA (so during replication). The exonuclease proof reads the strands as it replicates but once its finished replication, it won't be able to tell if a base was swapped with another. Also some aren't simply base substitutions in which case it would be harder to tell there was a mutation.

Errors in transcription replication are not significant as mRNA and proteins do not get passed on, they simply get degraded if they dont work (excluding retrovirus mutations).

 

[Prateek]

They happen to DNA and usually during replication or just in general they can happen anytime due to UV, radiation or other agents that can cause mutations in the DNA.

Also, the exonuclease activity does try to correct many of the mutations, but this system is not 100% proof and some errors get by

 

[Rabolisk]

Mutations are changes to the DNA of the genome. These can be on discrete somatic cells, which won't be passed down to offspring.

There are many ways to categorize mutations.
Frameshift is when you add or delete a number of nucleotides, shifting the entire code, and generally resulting in severe problems.

Missense mutations result in a different amino acid. Nonsense mutations result in a stop codon. Silent mutations don't cause any effect.

Gain-of-function and loss-of-function mutations are exactly what they sound like.

Mutations can be caused by chemicals, radiation, viruses, etc. They can also spontaneously occur. Exonuclease activity probably corrects a lot of mutations and errors, but nothing is foolproof.

 

[sangria1986]

Also mutations in somatic cells never get passed along. Only in germ. Also the most significant types are frameshift if they happen in non-triplet form. Other types are choromosomal-deletion duplication inversion translocation. These are passed on if they happen during meiosis.

Only eukaryotes can have duplication

 

[sugarbabee0]

Thanks for the responses guys

So the mutation occurs at the DNA level either during or after replication. Exonuclease tries to fix it up but some get by...

And how about RNA mutations (especially since no RNA exonuclease)? I'm still not sure I understand if there are any.. or not (either during transcription or translation)...

 

[fizzgig]

i would think sure, RNA errors will happen while transcribing, and sure, maybe a wrong amino acid can be added during translation. but think about how ephemeral these are in the grand scheme of things - that's why they're not the point of discussion in your book/notes.

1 mRNA being screwed up will make a lot of screwy proteins, but there are probably a lot of other mRNAs for that same DNA segment that are making fxnl protein at the same time. so whatever. screwy rRNA, again, who cares, you can't make a ribosome out of it and it is degraded. a translation error inserting a wrong amino acid when the mRNA was correct is even less important - it's just ONE protein affected.

the blueprint for building a million houses is way more important than sending out one incompetent worker who screws up all 1000 of his, which is more important still than sending out a competent worker that happens to build one of his 1000 houses wrong.