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GENE TRANSFER
MECHANISM
Presented by:JEEVITHA.H.A
II Sem, MSc.
CONTENTS
Definition of gene
Gene transfer mechanism
Types
Bacterial transformation
Transduction
Conjugation
Mechanism
Application
References
GEnE …???
A gene is the molecular unit of
heredity of a living organism.
GENE TRANSFER
MECHANISM????
• It is the mechanism where a
particular gene is transferred from
donor cell to recipient cell….
•It is the insertion of copies of a gene into
living cells.
•The desired gene may be microinjected
directly into the cell or it may be inserted
into the core of a virus by gene splicing and
the virus allowed to infect the cell for
replication of the gene in the cell's DNA.
TYPES
• Bacterial Transformation
• Transduction
• Conjugation
• Host cell restriction
• Complementation
• Transfection
TRANSFORMATION
The process by which a donor DNA
molecule is taken up from the external
environment and incorporated into the
genome of a recipient cell….
History
• First discovered by Frederick Griffith
in 1928 in Diplococcus pneumoniae.
• In 1944,Avery and co-workers
showed that DNA was responsible
for transformation.
KEY POINTS
• Energy requiring process.
• Proteins and enzymes are required.
• Maximum frequency of competent cells
during late log phase.
• Naturally occuring transformation.
Types
• NATURAL TRANSFORMATION
• It is a bacterial adaptation for DNA transfer
that depends on the expression of numerous
bacterial genes.
• Competent development in Bacillus subtilis
require about 40 genes.
• Usually requires bacteria of same species.
ADAPTATION FOR DNA
REPAIR
• Competence is induced by DNA
damaging conditions.
• Mitomycin C and fluoroquinoline.
• UV light
MECHANISM
STEP-1
• A competent cell binds a large double
stranded fragment of DNA at specific
receptor sites on the surface of the
bacterium.
• One of the DNA strands is hydrolyzed by
a membrane bound exonuclease,
providing energy to help DNA transport
across the membrane.
STEP-2
• Induced proteins binds to single
stranded donor fragments.
STEP-3 (A)
• The single stranded fragment of
DNA is coated with DNA –binding
protein and recombination proteins
search for the same or very similar
DNA sequences in the chromosome
of the recipient cell.
STEP-3 (B)
• Remainder of the ssDNA fragment
is degraded.
APPLICATIONS
•
Transformation is one of the many
ways of today to create recombinant
DNA, DNA in which genes from two
different sources-many times different
species- are combined together and
placed into the same molecule or
organism. This manipulation of genes is
called genetic engineering and has many
practical applications in the world today.
This is a very basic technique that is
used on a daily basis in a molecular
biological laboratory. The purpose of
this technique is to introduce a foreign
plasmid into a bacteria and to use that
bacteria to amplify the plasmid in order
to make large quantities of it. This is
based on the natural function of a
plasmid: to transfer genetic information
vital to the survival of the bacteria.
TRANSDUCTION
• The process by which DNA transferred
from one bacterial cell to another by
bacteriophage.
KEY POINTS
• VIRULENT PHAGES - are those that
immediately lyse and kill the host.
• TEMPERATE PHAGES – can remain
within the host cell for a period
without killing it.
TYPES
• GENERALISED TRANSDUCTION
• SPECIALISED TRANSDUCTION
Generalized Transduction
• In generalized transduction, a small piece of the
host cell’s degraded DNA is packaged within a
capsid, rather than the phage genome.
• When this phages attaches to another bacterium, it
will inject this foreign DNA into its new host.
Specialized
Transduction
•Occurs via a temperate phage.
•When the prophage viral genome is cut from the
host chromosome, it sometimes takes with it a
small region of the host bacterial DNA.
•These bacterial genes are injected along with the
phage’s genome into the next host cell.
•Specialized transduction only transfers those
genes near the prophage site on the bacterial
chromosome.
Specialized transduction occurs via a
temperate (can in corporate its genome
in to the bacterialcell) phage.
•The DNA of lambda is inserted into the
host DNA at the site adjacent to the
galactose genes
•On induction, Under rare conditions,
the phage genome is excised incorrectly
•A portion of host DNA is exchanged for
phage DNA, called lambda dgal ( dgal
means "defective galactose“ )
•Phage synthesis is completed
•Cell lyses and releases defective phage
capable of transducing galactose genes
APPLICATIONS
• Resistance to anti-biotic drugs.
• Correcting genetic diseases by direct
modification of genetic errors.
CONJUGATION
• Conjugation is a process in which
bacteria makes contact with each other
through pilus formation and genetic
material is transferred unidirectionally
from donor to recipient cells.
• F factor directs conjugation.
• F+ cells
• F- cells
• Hfr
• F’ factor
Mating types in
bacteria
Donor
•F factor (Fertility factor
•F (sex) pilus
Donor
Recipient
• Lacks an F factor
Recipient
Physiological States of F
Factor
• Autonomous (F+)
–Characteristics of F+ x Fcrosses
• F- becomes F+ while F+
remains F+
• Low transfer of donor
chromosomal genes
F+
• Integrated (Hfr)
– Characteristics of Hfr x F- crosses
• F- rarely becomes Hfr while Hfr
remains Hfr
• High transfer of certain donor
chromosomal genes.
F+
Hfr
• Autonomous with donor genes (F’)
– Characteristics of F’ x F- crosses
• F- becomes F’ while F’ remains F’
• High transfer of donor genes on F’ and low
transfer of other donor chromosomal genes
Hfr
F’
Mechanism of F+ x F- Crosses
• Pair formation
– Conjugation
bridge
• DNA transfer
– Origin
of
transfer
– Rolling circle
replication
F+
F-
F+
F-
F+
F+
F+
F+
Mechanism of Hfr x FCrosses
• Pair formation
– Conjugation
bridge
• DNA transfer
Hfr
F-
Hfr
F-
– Origin of transfer
– Rolling
circle
replication
• Homologous
recombination
Hfr
F-
Hfr
F-
MechanisM of f’ x f- Crosses
• Pair formation
– Conjugation
bridge
• DNA transfer
F’
F-
F’
F-
F’
F’
F’
F’
– Origin of transfer
– Rolling circle
replication
•Lederberg and Tatum
Showed that genetic information could
be transferred from one bacterium to
another.
• Davis
• Showed Conjugation requires direct,
physical contact between cells.

Hayes
•CONJUGATION is polar.
•Requires the F+ plasmid.
•Recipient becomes F+ once conjugation is
complete. Noted that only rarely did auxotrophs
become prototroph’s after conjugation.
•Consequences of Hfr conjugation
•Can transfer bacterial genes other
than the F+ genes
•Many different genes could be
transferred.
•Recombination
variability occurs.
or
Genetic
Schematic drawing of bacterial conjugation.
Conjugation diagram 1- Donor cell produces
pilus. 2- Pilus attaches to recipient cell and
brings the two cells together. 3- The mobile
plasmid is nicked and a single strand of DNA
is then transferred to the recipient cell. 4Both cells synthesize a complementary strand
to produce a double stranded circular plasmid
and also reproduce pili; both cells are now
viable donors.
APPLICATIONS
• Conjugation is a convenient means for transferring
genetic material to a variety of targets. In
laboratories, successful transfers have been
reported from bacteria to yeast, plants,
mammalian cells and isolated mammalian
mitochondria.
• Conjugation has advantages over other forms of
genetic transfer including minimal disruption of
the target's cellular envelope and the ability to
transfer relatively large amounts of genetic
material.
REFERENCES
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General Microbiology ( 5th edition )
Roger.Y.Stanier
Prescott’s Microbiology ( 8th edition )
Joanne.M.Willey
Linda.M.Sherwood
Christopher.J.Woolverton
‘BROCK’-Biology of Microbiology ( 11th edition )
Michael.T.Madigan
John.M.Martinko
Principles of Genetics
D.Peter Snustad
Michael.J.Simmons
John.B.Jenkins
Microbial Physiology and Microbial Genetics
B.D.Singh
R.P.Singh
Any
queries…???