Microbial Genetics Gene Transfer SP10

8/8/2019 Microbial Genetics Gene Transfer SP10

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Microbial Genetics

Gene Transfer

Chapter 8


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Genetic Recombination

Vertical genetransfer: Occursduring reproduction

between generationsof cells.

Horizontal gene

trans

fe

r: The transferof genes between cellsof the same

generation.


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Horizontal Gene Transfer

1. Transformation

2. Transduction

3. Conjugation


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1. T R A N S F O R M A T I O N

Genes are transfer red from one

in solution.

a. naturally occurs in a few bacter iaCompetent

b. bacter ia madecompetent ar tificiallyc. approx 20 genes


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Figure 8.24

Genetic Transformation


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Transformation


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2. Transduction

Transport of DN A from one bacter ium toanother bacterium by a virus

a. Generalized vsspecialized transduction

b. dur ing assembly: defective phage

c. Defective phagecan now transfer DN Afrom host (the Donor) to anotherbacter ium (Recipient)


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Figure 8.28

Generalized Transduction by a Bacteriophage


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2

3

4

5

6

Figure 13.13

Specialized Transduction


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Trans

duc

tion


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3. C O N J U G A T I O N

D i rect transfer of DN A from bacterialdonor cell to a recipient.

a. Mediated by plasmidb. requirescell to cell contact: established

by pil i in most G ram negativecells

c.

Spread of Antibiotic resistanced. Plasmid or Chromosome moves as


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Conjugation:Transfer of a plasmid

1. Donor cell has F plasmid and hence isrefer red to as

2. Recipient cell lacks F plasmid, henceF

3. Only onestrand of plasmid

trans

fe

r re

d4. After conjugation, both donor andrecipient become F+


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Figure 8.27a

Conjugation in E.coli


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Conjugation
http://../animations_library/anim0020.exehttp://../animations_library/anim0020.exe


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Plasmids

1.

One/Many types of plasmids in a singlecelleg. F , R ,T i.

2. A few or several copies of a plasmid(high/low copy number plasmid)

3. Narrow/broad range plasmids

4. Nonessential functionscarr ied onplasmids-spontaneous deletion

5.

replicate


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Conjugation:Transfer of a plasmid

and chromosomal DN A1. Donor cell is Hfr : has F plasmid. How

is it different from F+?

2. Recipient cell lacks F plasmid, hence F

3. Hfr cell conjugates with F cell

4. End result: H fr cell and recombinantF cell


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Figure 8.27b



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Figure 8.27c



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Conjugation: Chromosomal transfer


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Figure 8.30a, b

Transposons Segments of DN A that can move from one

region of DN A to another Contain insertion sequences for cutting and

resealing DN A (transposase)

Complex transposonscar ry other genes


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TRANSPOSONS

all transposonscontain info needed toinsert selves in genetic material

frequency similar to spontaneousmutations

involvement in evolution of organisms

--can car ry genes with them;

e.g. antibiotic resistance


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Transposons

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Microbial Genetics Gene Transfer SP10