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