Describe - Gene Transfer
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Transcript of Describe - Gene Transfer
Describe: gene transfer
b.stev
METHODS - gene transfer between
bacteria:
binary fission
conjugation
transformation
transduction
transposons
REPLICATES before cell division:two daughter cells attached>interior of cell
membrane membrane elongates, chromosomes move apart cell doubles in size: chromosomes separate the cell THEN “pinches”pinches” inwards... a new cell wall forms that separates the two new cells and their chromosomal replicas
ALL genetic material contained is transferred to the daughter cell
(Barnes S. N, Curtis H, 1989)
Binary fission
cell wall
chromosome
cell membrane
theta replication
growth of cell
NEXT
REPLICATION
new cell wall forms
REPLICATED bacterial
cells
(two identical daughter
cells)
This type of replication is known as:
THETA REPLICATION
a bi-directional motion
DNA helix
unwinds/ replicates/ rewinds
cell F-cell F+
bacterial chromosome
F plasmid
bacteria join: pili
transfer of F plasmid
cell F+
transfer provides: COMPLEMENTARY DNA
CONJUGATION
PLASMIDS are small pockets of DNA that occur in bacteria carry genetic material for a specific purpose plasmids often conjugate to another bacterium
THIS:provides the bacterium with complementary DNA
KNOWN AS,”rolling circle replication”
plasmid moves to bacterium via the use of an extension made by host [carrier] cell:
- this extension is called: pili
(Barnes S. N, Curtis H, 1989)
DNA fragment is absorbed through the cell membrane and utilised in function (expressed) enhanced drug resistance from the
acquisition
of plasmids OR/& DNA
fragment(s)
occurs in crowded environments like a rich
soil
OR within the human intestinal
tract
Transformation
NOTE: not significant in contribution to thedispersal of antibiotic resistant genes
Transduction
SPECIALISED>
prophage – the altered bacterial DNA performsBINARY FISSION that creates replicates
though the replicates differ:ONE may produce virus cellsOTHER creates defective virus cells that seek to perform the process of: generalised transduction
(Pommerville J.C, 2004)
Insertion Sequencessmall segments DNA: about
1000bpINSERTION OCCURS AT:
one/ more sites on bacterial chromosome/
plasmids
no genetic information otherother thanthan abilityability to insertinsert
form copies of themselves & these move to other
areas of the chromosome
can interrupt a coding sequence of protein(s)
may be some cause behind: spontaneous
mutation
induces wrong protein(s)/ no protein(s) forms
o interrupts genetic code of the gene
o appears NOT be replaced once,’disembarked’
o can move from: plasmid/plasmid plasmid/chromosome chromosome/plasmid
o thought to serve as evolutionary driving force: development, fertilized egg to mature organism
Transposonslarger insertion sequences that have the
ability:ability: carry information such as antibiotic resistance
C C C T A A T T A G G G
G G G A T T A A T C C C
inverted sequence of repetitive bases: ability to move/ insert & disembark
coded sequence of information
TRANSPOSON
Genetic Transfer &
dissemination of drug resistanceTransfer, causes increase in bacterial populationthat have the abilityability to resist specific drugs:
Evolved to alter their manufacture of the required protein(s), so the drug pathway:
has altered chemical attachment points
enzymes can counteract chemical bonding
other metabolic means are able to be used
OVERUSE & MISUSE ENCOURAGES RESISTANT FORMS:
1968-71> Guatemala; 12,000 people died to a resistant form of: S.dysenteriae
ANTIBIOTICS causes the sensitivesensitive cells to die, stimulates resistant cells: grow & to thrive increasing numbers
HOSPITALS: care taken to prevent resistant strains overtaking the susceptible strains
especially:E.ColiP.AeruginosaS.MarcesensProteus
(Pommerville J.C, 2004)
PLASMIDS and TRANSPOSONS cause the most movement of the antibiotic resistant genes
resistance can occur in harmless bacteria that transfer this to pathogenic bacteria:
ALSO increasing potential of disease
LIVESTOCK fed with antibiotics is traceable
to human consumption; and thus may also
through the cyclecycle of bacterial growth:bacterial growth: gain
resistance over the time of exposure to the
drug: ALSO increasing potential of disease
Bibliography
Campbell N. A, Reece J. B. (2005). Biology (7th ed.). San Francisco: Benjamin Cummings
Pommerville J.C. (2004). Alcamo’s – Fundamentals of Microbiology (7th ed.). Massachusetts: Jones and Bartlett.
Barnes S. N, Curtis H. (1989). Biology (5th ed.). New York: Worth