chapter 8 Microbial Genetics Flashcards
genetic change in bacteria:
What are the two methods?
mutation and horizontal gene transfer
define what mutation is
is a change in the nucleotide sequence of DNA
it also may cause a change in a protein encoded by gene
is a change in the nucleotide sequence of DNA, it also may cause a change in a protein encoded by gene
mutation
define what horizontal gene transfer is:
genetic info is passed from one living cell go another cell of the same generation for example : plasmid transfer
genetic info is passed from one living cell to another cell of the same generation
horizontal gene transfer
True or false.
Horizontal gene transfer:
in either case:
Change is stable, and passed on to progeny
true
Mutations :
what are the two steps:
- Base substitution
- Frameshift mutation
define base substitution (point mutation)
a single nucleotide is replaced by another nucleotide
- when DNA replicates- results in a substituted base pair
when DNA is transcribed and translated can result in an incorrect amino acid in the protein - missense mutation
when dna is transcribed and translated can result in an incorrect amino acid in the protein
missense mutation
describe what missense mutation
when DNA is transcribed and translated can result in an incorrect amino acid in the protein
frameshift mutation
insertion- one or two nucleotides added to the gene
deletion- one or two nucleotides removed from the gene
- changes the reading frame if the mRNA
sequence of amino acids is changed “downstream” of mutation site
——- almost always results in a non functional protein
how do mutations occur?
name the two fundamental steps
1.spontaneous mutation
2.induced mutation
occur in absence of mutagens, due to occasional mistakes during DNA replication
spontaneous mutation
define what spontaneous mutation means
occur in absence of mutagens, due to the occasional mistakes during DNA replication
define what induced mutation is
occur when DNA damaging agents cause changes in DNA sequence - mutagens , for example : radiation, some chemicals
regardless of origins, mutations can result in
1.no effect on the protein (remains functional)-silent mutation
2.a protein with a different aminoa cid sequence that may have an altered function - missense mutation
3.Premature stop codon- incomplete (truncated) protein, usually non functional- non sense mutation
no effect on the protein (remains functional ) is
silent mutation
define silent mutation
no effect on the protein (remains functional)
A protein with different amino acid sequence that may have an altered function
missence mutation
define what missense mutation is
a protein with a different amino acid sequence that may have an altered function
Premature stop codon- incomplete (truncated) protein, usually nonfunctional
nonsense mutation
define what nonsense mutation is
premature stop codon-incomplete (truncated) protein, usually non functional
this is a self replicating, dsDNA molecules, and it contains non essential genes
for example : genes for toxin production
this is what we call plasmids
define plasmids
self replicating, dsDNA molecules and it contains non essential genes
for example: genes for toxin production
name the three kinds of plasmids
F plasmids
R plasmids
Vir plasmids
what is a F plasmids?
another term is fertility factors, it carry genes to make F pilus (or sex pilus)
- it is also involved in conjugation (transfer of genetic information)
what is r plasmids?
this is resistance factors , carry genes for antibiotic resistance
what is vir plasmids?
virulence factors, carry genes for toxin production
carry genes for antibiotic resistance
R plasmids
involved in conjugation
F plasmids
carry toxic gene production
vir plasmids
what are the three basic methods of horizontal gene transfer?
transformation
transduction
conjugation
define transformation
pieces of naked DNA are taken up by a bacterial cell example : from dead cells, or released plasmids
these pieces can be integrated into the chromosome recombination , can be passed to progeny and become a stable part of the genome
define what transduction is
is a small fragments of DNA transferred between bacteria by bacteriophage
- viruses that infect bacteria
Phage attaches to bacterial cell wall-inject its DNA into the cell
Phage DNA is replicated inside the bacterial cell
Define more characteristics about Transduction
Phage DNA also encodes enzymes that cut the bacterium’s DNA into fragments
As new phages are being assembled, some accidentally receive a piece of bacteria DNA instead of phage DNA
- transducing particle
the transducing particle can then carry bacterial genes to another cell
injection mechanism is still fully functional
But, bacterial DNA is injected into the cell
True or false.
Transduction:
If the injected DNA recombines with the existing chromosome it becomes unstable genetic elements, however it will still be passed to progeny
false
conjugation (bacterial mating) :
mediated by genes encoded on a F factor
conjugation(bacterial mating): Transfers occurs when a:
Donor cell (F+)- forms an F pilus and uses it to attach to a recipient cell (F+)
Pilus retracts bringing the cell together
The donor cell replicates the F factor as a copy is passed to the recipient
The recipient becomes an F+ cell.
