inheritance and information flow Flashcards
what is vertical gene transfer
when two gametes fuse together and homologous chromosomes exchange genetic information- the genetic information is transferred from one generation to the next
what is horizontal gene transfer
the transmission of genetic information between different organisms
what are the three different ways prokaryotes exchange genetic information
1) transformation
2) conjugation
3) transduction
what is transformation
when the prokaryotes uptakes DNA from the environment and recombines it within its own genome
define a competent cell
cells which could take up DNA from the environment
it is a transient state depending on the cells physiological state
who discovered transformation
Frederick Griffith 1928 using streptococcus pneumoniae
outline the mthods of frederick griffiths experiment when discovering transformation
- involved injecting capsule free and capsuled bacteria into mice
method A= live capsule free= mice died as well as bacteria
method B=live capsule bearing=mice die bacteria live
method c- heat treated dead capsule bearing = mice live
method D- live capsule bearing injected with dead capsule bearing = mice die and bacteria live with a capsule
what did frederick griffith conclude in his transformation experiment
R cells aquired the capsule gene from DNA released when s cells were killed by heat, therefore streptococcus pneumonia is naturall compotent
outline the mechanism behind natural transformation
1) exogenous dsDNA binds to proteins of the competent cell membrane
2) the dsDNA is fragmented into smaller pieces
3) one strand of the DNA is degraded by nuclease while the other enters cells
4) the strand in the cell is coaded by transformation specific DNA binding proteins
5) the strand is homologous to existing DNA region so is intergrated in the chromosome
6) RecA invaded the hologous region in the chromosome displacing existing strands and replacing with DNA
6) when the cell divides only one daughter cell inherits transforming strand
what is RecA
a protein essential for the repair and maintenance of DNA
what is a nuclease
an enzyme which cleaves the chains of nucleotides into smaller acids therefore free DNA is short lived in the environment
what is gene cloning
recombinant DNA is introduced into cells artificially
how is DNA introduced into bacteria artificially
1) chemically competent cells and heat shock
2) electrocompetent cells and an electroporator
outline the method of introducing DNA into bacteria using heat shock
1) cells are treated with chemicals (CaCl2) which alter the cell membrane permability allowing uptake
2) the calcium ions are attracted to negatively charged DNA and membrane producing a electrostaically neutral enviro
outline the method of introducing DNA using electroporation
1) introduce the gene to the cell
2) apply an electric pulse which forms pores in the cell membrane allowing the gene to enter
3) after the electric pulse the pores reseal and the gene remains in the cell
in cloning why are plasmids used more
the transformartion efficiency is higher as they cant be degraded by nucleases as they have no exposed ends compared to linear DNA which can be
what is conjugation
a way of genetic exchange amoung microbes based on the ability of certain plasmids to transfer from cell to cell
what is conjugation responsible for
1) horizontal gene transfer events
2) rapid spread of antibiotic resistance
what is an F-plasmid/ F-factor/ sex factor
the conjugative plasmid
how does conjugation in gram negative batceria work
1) the sex pilus of the donor (f+) attaches to recipient (f-)
2) the sex pilus retracts dragging the cells together
3) a single strand of plsamid is cut and unwound and the DNA is transferred to recipient cell and donor synthesises new strand
4) in the recipient a second strand is replicated where it becomes F+ and a new donor cell
what are high frequency recombination cells
when the F-factor in the conjugative plasmid is integrated into the chromosome of the donor bacteria by site specific recombination
= the regions of plasmid sequecence and chromosome must be similar
what does site specific recombination involve
1) specific DNA sequences
2) two DNA partners
3) a speacilised recombinase prtoein which is responsible for recognising the sites and breaking and rejoining the DNA
outline conjugation in high frequency recombination cells
1) once integrated into theHfr cell the cell now contains the F-factor which can produce a sex pili
2) the cell connects with donor and gene in chromosome is transmitted to recipient
3) the length of time of attachemnt defines how much DNA is transferred
4) once in donor the DNA fragment integrates by homologous recombination in the chromosome
what is the differences between conjugation in gram positive and negative bacteria
- mechanisms which establish celll to cell contact
- positive clump together to bring donor and recipient close, they dont form a sex pilus
outline conjugation in gram positive bacteria
1) recipient produces a pheramone which interatcs with a plasmid of donor cell
2) plasmid in donor cell encodes for genes producing aggregation substances
3) these substances migrate to the cell surface
4) the substances bind to bidning substances on recipient membrane
5) cells clump and genetic exchange occurs
what is quorum sensing
used by gram positive bacteria to locate donor cells for conjugation
what is transduction
the transfer of gentic material by bacterial virus (a bacteriophage) where when the phage packs DNA during assembly it carries that DNA from one bacteria to the next
what mistakes can occur during transduction
1) phages randomly pack and exchange any of the hosts genes (generalised transduction)
2) phages only pack and exchange specific genes from the host (specialised transduction)
when does generalised transduction occur
during the lytic phase
1) phage injects DNA
2) phage enzymes degrade host DNA
3) cells synthesise new pahges and incroporate phage DNA and accidently some of the bacteria host DNA
4) tranducinh phage injects some of host DNA which is then incorporated into recpipient chromosome
when does specialised transduction occur
during the lysogentic phase before phage excises
outline the process of specialised transduction
1) phage DNA is integrated into bacterial chromosome as a prophage
2) normal phage excision produces a circular phage again
3) abnormal excision results in some of neighbouring bacterial DNA being carried over in the cirucalr phage
what is homologous recombination
when genetic information is exchanged between two similar or identical molecules of double or single stranded nucleaic acids
