Chapter 8: Microbial Genetics - Mutations Flashcards
What are two methods of genetic change in bacteria?
- mutation
- horizontal gene transfer
What is a mutation?
- a change in the nucleotide sequence of DNA
What can mutations cause?
- may cause a change in a protein encoded by a gene
What is horizontal gene transfer?
- genetic info is passed from one living cell to another cell of the same generation
ex. plasmids
In either cases of mutations and horizontal gene transfer, is change stable?
yes, change is stable and is passed onto progeny
What are two types of mutations?
- base substitution (point mutation)
- frameshift mutation
What is a base (point) substitution?
- a single nucleotide is replaced by another nucleotide
Why does a point mutation occur?
- when DNA replicates, it results in a substituted base pair
- so when DNA gets transcribed and translated, it results in an incorrect AA in the protein
What is an example of a point mutation?
- missense mutation
What is a frameshift mutation?
insertion or deletion of nucleotides to the gene
What is an insertion?
- one or two nucleotides added to the gene
What is a deletion?
- one or two nucleotides removed from the gene
What does a frameshift mutation cause? (2)
- changes the reading frame of the mRNA
- then the sequence of AA is changed downstream of the mutation site
What do frameshift mutations result in?
- almost always a non-functional protein
What are two ways that mutations occur?
- spontaneous mutation
- induced mutation
What is spontaneous mutation?
- occurs in the absence of mutagens, due to occasional mistakes during DNA replication
What is induced mutation?
- occurs when DNA damaging agents cause changes in DNA sequence (mutagens)
What are mutagens?
- DNA damaging agents
What are some examples of induced mutations?
- radiation, some chemicals
REGARDLESS of origin, mutations can result in what three things?
- silent mutation
- missense mutation
- nonsense mutation
What is a silent mutation?
- No effect on the protein (remains functional)
thus no change in AA sequence
What is a missense mutation?
- A protein with a different amino acid sequence that may have an altered function
What is a nonsense mutation? (2)
- premature stop codon
- results in an incomplete (truncated) protein that is usually non-functional
