Exam 3 - Lecture 17 Flashcards
what is the most common type of mutation?
point mutation
what are the two types of point mutations?
- SNPs (single nucleotide polymorphism; single nucleotide is changed)
- Indels (insertion or deletion of nucleotides)
consequence of mutations depends on:
- type (SNP, indel, etc.)
- location (within a gene, between two genes)
what does CDS stand for?
coding DNA sequence
what does IG stand for?
intergenic
what can a SNP mutation in a CDS result in?
- silent mutation
- missense mutation
what can an indel mutation in a CDS result in?
frameshift mutation
what is a silent mutation?
no amino acid change i the resulting polypeptide
what is a missense mutation?
amino acid change in the resulting polypeptide
what is a frameshift mutation?
multiple amino acid changes/early stop codon
what does a point mutation in an IG cause?
- usually no effect
- can alter gene expression if in an area like a promoter
what is mismatch repair and what enzyme carries out this process in E. coli?
- a type of excision repair
- mismatch correction enzyme (MutS) scans newly synthesized DNA for mismatched pairs
- mismatches are removed and repaired by DNA pol and DNA ligase
in E. coli, new strands will be ___________ and old strands will be __________ to distinguish between them for mismatch repair.
unmethylated; methylated
will mismatch repair be carried out on a methylated or unmethylated strand?
unmethylated
do eukaryotes undergo vertical or horizontal gene transfer? how about prokaryotes?
- vertical: euks
- horizontal: proks
true or false: horizontal gene transfer can allow gene transfer between different species.
true
for HGT DNA to be inherited by offsrping, it must become _______ and find a way to ___________
stable; replicate
what are two ways HGT DNA can become stable once trasnferred?
- self replication
- integrate into the chromosome
what is recombination?
integration of transferred DNA into the host genome
what are two major types of recombination?
- homologous recombination
- site specific recombination
what are the three important differences between site specific has from homologous recombination?
- it does not require long regions of DNA homology
- recombination occurs at specific target sites in DNA molecules
- mediated by specific enzymes called recombinases
what are two major types of transmissible DNA?
- transposable elements
- plasmids
what are three mechanisms for horizontal gene transfer?
- conjugation
- transformation
- transduction
which domains of life have transposable elements?
all three
what is transposition?
small segments of DNA moving about the genome (they are sometimes called jumping genes)
who discovered transposable elements?
Barbara McClintock in 1940s
what are the simplest transposable elements?
insertion sequences (IS)
what are composite transposons (Tn)?
transposable elements containing “extra” genes flanked by two insertion sequences
what are unit transposons?
- they are between being an IS and a composite Tn
- it’s like an extended IS than can contain extra genes
- basically a gene flanked by ONE transposase gene
what are inverted repeats? what do they mark?
- short stretches of identical nucleotides in opposite orientations
- marks the ends of the IS or Tn
what is transposase?
an enzyme responsible for site specific transposition
what are direct repeats?
- host DNA that is the site for insertion
- duplicated during insertion
what are the two types of transposition?
- simple transposition (cut and paste)
- replicative transposition (copy and paste)
what are retrotransposons?
RNA copy of the transposable element is made and is transcribed back into DNA to integrate at the new site
what are plasmids?
- small, extrachromosomal circular DNA molecules
- exist and replicate independently of chromosome
- contain non-essential genes that confer selective advantages to the host (drug resistance, virulence, etc.)
true or false: cells cannot have more than one plasmid.
false
what are episomes?
plasmids that can integrate reversibly into the host chromosome
what are conjugative plasmids?
plasmids that can transfer copies of themselves to other bacteria during conjugation
true or false: plasmids can exist independently of the host chromosome.
true
what structure facilitates conjugation?
sex pilus/F pilus
true of false: donor chromosomal genes are usually transferred during conjugation.
false; they aren’t (usually)
plasmids are replicated via what method?
rolling circle method
at the end of successful F+ x F- mating, what types of cells are present at the end?
two F+ cells
what is the synthesis of the complementary strand in rolling circle replication similar to?
similar to lagging strand synthesis
in the rolling circle method, which end of the nicked plasmid allows for new strand synthesis?
the 3’-OH end
true or false: the F plasmid is an episome. why?
true; because it can reversibly integrate itself onto the host chromosome
where does integration of the F plasmid occur on the host genome?
insertion sequences
when the F factor is not integrated onto the host chromosome, the cell is considered:
F+
when the F factor is integrated into the host genome, the cell is considered:
HFr
what does HFr stand for?
high frequency recombination
true or false: conjugation cannot occur between HFr and F- strains.
false; it certainly can
in conjugation between HFr and F- strains, an ____________ copy of the F factor is transferred
incomplete
true or false: donor chromosomal DNA is transferred during HFr x F- mating
true
what characterizes an F’ plasmid?
- this is when the F factor is incorrectly excised from the host chromosome
- happens with HFr plasmids
what is transformation?
uptake of extracellular DNA by a bacterial cell
bacterial cells that have the ability to take up DNA from the environment are:
competent
for linear DNA to be stably transformed, it must:
integrate into the chromosome
what is transduction?
the transfer of bacterial genes by viruses
match the following:
- lytic cycle
- lysogenic cycle
a. viral DNA integrates into host genome (becoming a prophage)
b. host cell is destroyed
1b
2a
what is phage mediated transduction?
host (bacterial) gene transfer that is facilitated by bacteriophages
true or false: phage mediated transduction is typically an intentional process.
false; it’s typically accidental
what are the two types of phage mediated transduction?
- generalized transduction
- specialized transduction
match the following:
- errors in the lytic cycle
- errors in the lysogenic cycle
a. generalized transduction
b. specialized transduction
1a
2b
true or false: in generalized transduction, any part of the bacterial genome can be transferred.
true (“generalized”)!
generalized transduction occurs due to mistakenly packaged:
bacterial DNA into viral proteins (like the phage head)
how much viral DNA is packaged in with bacterial DNA during generalized transduction?
none!
specialized transduction occurs due to incorrect:
excision of the prophage from the host genome
true or false: in specialized transduction, the new virions will receive some of the viral genome and some of the bacterial genome.
true!
in specialized transduction, where does the transferred host DNA come from?
the host DNA surrounding the viral integration site
true or false: mutations cannot cause antibiotic resistance.
false; they do, and they do so spontaneously
what are two ways antibiotic resistance can occur?
- mutations
- horizontal gene transfer
resistance genes can be found in what three places?
- bacterial chromosomes
- transposons
- plasmids
