chapter 6 part 2 Flashcards
when does transformation occur
when a recipient cell takes up a fragment of donor DNA from the surrounding growth medium
what is transformation used for?
the introduce DNA in the lab to microbial cells, plant cells, & animal cells
-it is naturally occuring mechanism than can be used to produce accurate maps of bacterial genes
mapping genes that are closely linked
how long is transforming DNA typically?
usually shorter than 100 kb
cotransformation
simultaneous transformation of two or more genes
what is transformation preceded by in natural transformation?
lysis (the breakage of a donor cell)
what is the passage of DNA into a recipient accompanied by in natural transformation?
degradation of one of the strands & the remaining strand aligns with complementary regions of the recipient chromosomes
what does the alignment of donor & recipient DNA trigger in transformation?
excision of one strand of recipient DNA & replacement with donor DNA, forming a heteroduplex
what is the daughter cell that is transformed called & what does the other daughter cell do?
transformant
the other daughter cell retains the recipient chromosome original DNA strand & so is unchanged
how many steps is the lytic cycle?
6
describe the lytic cycle
- attachment of the phage to the host cell
- injection of the phage chromosome into the host followed by circularization of the phage chromosome
- replication of phage DNA using host proteins & enzymes
- transcription & translation of phage genes
- packaging of phage chromosomes into phage heads
- lysis of the host cell, & release of progeny phage particles
temperate phages
they have an alternate, temporary life cycle involving integration of the phage chromosome into the bacterial chromosome (lysogeny /l ytic cycle)
lysogenic cycle
- attachment & injection are the same as the lytic cycle
- integration of the phage chromosome into the host chromosome via recombination at a specific DNA sequence found in both chromosomes
- excision of the prophage in response to an environmental signal, through a reversal of the site-specific recombination leading to integration
- resumption of the lytic cycle, beginning with the phage-chromosome replication
when is the phage chromosome called the prophage?
once the phage is integrated into the host chromosome
transduction
the transfer of genetic material from a donor to a recipient cell by way of a bacteriophage
what are bacteriophage consisted of?
composed of an icosahedral head, hollow protein sheath, & sometimes a set of tail fibers
what is bacterial transduction mediated by?
bacteriophages
the bacteriophage injects a donor cell & some progeny phages accidentally incorporate a fragment of donor DNA rather than a copy of the phage chromosome
-these progeny phages then infect a recipient cell & inject the donor DNA (phage doesnt enter the cell)
what are the two types of transduction?
generalized transduction
specialized transduction
the conditions leading to transduction are due to …..
rare errors in packaging of phage DNA during the lytic cycle
what leads to production of a transductant bacterial strain?
the transfer of genetic material from a donor bacterium to a recipient via a phage
generalized transduction
the transfer of RANDOM bacterial genes, is carried out by bacteriophages that cannot distinguish between phage & bacterial DNA during packing of DNA into new phage particles
specialized transduction
carried out only by temperate phages & the only genes transferred are those close to the integration site
generalized transduction steps
- A normal P1 phage attaches to a donor bacterium and injects its DNA.
- The phage’s DNA is copied, and proteins are made.
- New phages are put together, but some (called generalized transducing phages) end up with a piece of the host’s DNA instead of their own DNA. This happens randomly based on size.
4.The host cell bursts, releasing all the new phages. - The generalized transducing phages attach to new recipient cells and inject their DNA.
- Inside the recipient, the donor DNA can combine with the recipient’s chromosome. (homologous recombination)
- This process creates a stable transductant strain.
in specialized transduction, what integrates into host chromosomes at specific sites?
temperate phages, such as lambda phage
att site
the integration site in the bacterial host chromosome
-the same 15 bp sequence
attp
integration site in lambda phage
attB
integration site in the e. coli host
why is the excision of the prophase usually the exact reversal of the integration?
because the attB & attP sites are identical
lateral gene transfer
the transfer of genetic material between individual bacteria or archaea & other organisms
what percent of genes in a genome are the result of LGT?
12%
what does LGT stand for
lateral gene transfer
what are the common characteristics of LGT genomic islands
-the group of genes in the island are like genes of distantly related species
-island region has a ratio of A-T/G-C different than the rest of the genome
genomic islands
area of LGT that is uniquely different than the rest of the genome
how big are genomic islands?
large (10-200kb)
how many genes do genomic islands contain?
multiple genes
what can LGT in bacteria lead to?
acquired pathogenicity islands
-promote host invasion & genes that produce toxic compounds
ex of pathogenicity islands
strains of e.coli have acquired pathogenicity islands that can cause diarrhea & meningitis
what does the aberrant excision produce in specialized transduction
specialized transducing phage
what includes the galK gene
lambdadgal+ specialized transducing phage
-can infect host but lacks genes needed to complete either lysis or lysogeny
what includes the bioA gene?
lambdadbio+ specialized transducing phage
-can induce lysis but lacks the genes needed for lysogeny
merozygote
a state when a partially diploid bacterial cell is produced
what can partial diploids be used for?
used to examine the mode of action of bacterial genes, & their regulation
what is called a partial diploid?
exconjugants that contain a complete F’ factor
-since they contain two copies of the bacterial chromosome genes found on the F’ factor
F’ cells
F’ factor containing all its own DNA plus a segment of the bacterial chromosome which comes from aberrant excision of the F factor from an Hfr chromosome
is complete transfer of bacterial chromosome accomplished in Hfr gene transfer?
no, it is too long
can linear DNA in the recipient cell re-circularize
no
what does Hfr stand for
high frequency recombination
