Effects of Mutation- Exam II

Micro 4130- Exam 2

Effects of mutations

Depends on the type of mutation and the function that the altered sequence (DNA or the RNA and protein that it encodes) has in the cell.

What mutations can tell you

The function that the altered sequence has in the cell

Intragenic mutation

Only affecting one gene/location

Extragenic mutation

Affects across several genes/locations

Consequences of a bp (or insertion/deletion of a few) mutation in a regulatory/promoter/SD site

Could alter nothing, promoter, regulator-binding site, SD sequence of mRNA, or 5’-UTR of mRNA. This could alter transcription or translation, or when/how much RNA/protein is made.

1/few bp alterations in the promoter sequence

Can greatly change the amount of transcription by changing spacing/identity of promoter sequence, changing DNAP binding.

Positive transcriptional control

Activators stimulate transcription

Negative control of transcription

Repressor inhibits transcription

Consequences of changes in sequence encoding a RBS/SD for translated RNAs

If the mutation increases/decreases the efficiency of the RBS then this increases/decreases the levels of the protein. Decreasing translation often increases mRNA degradation.

Consequences of a bp (for few bp) change in a gene that encodes an untranslated RNA

RNA can be affected at the level of stability (folding process/structure), function, or not at all. Changing the DNA will always change the RNA, but whether it affects the function of the RNA depends on where it is.

Mutation effects on tRNAs

Could affect modification sites. tRNA stability and function can be changed- might still be semi-functional but there will be defects in the cell.

Consequences of a bp mutation in a gene that encodes a protein

Could have no effect or change the synthesis (more or less produced), stability (folding process/structure), and function.

Consequences of bp change in ORF

Silent mutation, nonsense mutation, or nonsense mutation.

What are the bases on the codon chart

Correspond to the mRNA in the 5’ to 3’ direction

Rare codon

The tRNA that is associated with that codon is not abundant in the cell. This means that the ribosome takes more time in translation because there is a less likely chance that the right tRNA will come along.

Why rare codons are helpful

Have evolved to give breaks in/slow down tln so that the protein has a chance to fold properly.

Fast (optimized, common) codons

Get translated really fast, if the ribosome isn’t slowed down then the protein might not be folded properly before the next section of protein is made.

Why is is necessary to use the right slow/fast codons

To allow the ribosome to coordinate its speed of translation so that the proper residues of the protein can interact and fold together.

Effects that silent mutations can have

Change the amount/folding of protein made

Effects that missense mutations can have

Can change protein folding/stability/function

Effects that nonsense mutations can have

Truncated polypeptide could still be functional or be unstable and/or non-functional