Gene transfer mechanisms in bacteria

This presentation is about methods of gene transfer in bacteria.

1. Gene Transfer Mechanisms
in Bacteria
Prsented by:
Sanjay Kr Vishwakarma

2. Gene transfer mechanisms in bacteria
•Conjugation: orderly, deliberate transfer of DNA from one cell
to another; programmed by specialized genes and organelles.
•Transformation: uptake of environmental DNA into a cell
•Transduction: transfer of DNA from one cell to another
mediated by a virus

4. Properties of gene transfer in bacteria
•All are unidirectional (donor–recipient)
•Recombination requires two steps:
1.Transfer of DNA into the recipient cell, forming a merozygote(various gene
transfer mechanisms)
2.Crossing over that replaces a portion of the recipient genome (endogenote)
with the homologous portion of the donor genome (exogenote)
•Transfer is always partial

5. Conjugation

6. •Direct transfer via connection tube, one-way traffic from donor cells
to recipient cells.
•It is not a reciprocal exchange of genetic information.
•F
+
cells donor cells containing F factor
•F
−
cells recipient cells lacking F factor
•Sex Pilus –connection tube

7. Conjugation in E. coliis based on the F (fertility)
plasmid

8. Transfer of integrated F includes donor
chromosome
Unidirectional
transfer
Recombination
Partial transfer

9. DNA transfer during conjugation is time-dependent
Transfer of an entire E. colidonor genome requires about 1 hour (F
sequence is last to transfer)
The chromosome as a time function:
•Mix donor Hfrand recipient F-cells
•Interrupt transfer of DNA at various times
•Plate out cells to determine which genes were transferred within each
timeframe

10. Hfr azi
r
ton
r
lac
+
gal
+
str
s
X F
-
azi
s
ton
s
lac
-
gal
-
str
r

11. Transformation
DNA in the environment of a cell is taken into the recipient cell
forming a merozygote; then recombination occurs
•Competent cells: cells that take up DNA
•Transformants: cells that receive genetic material
•Cotransformed: cells that are transformed by two or more genes

13. Transduction
Transduction: Transfer of DNA from one cell to another mediated by
a virus; followed by recombination to integrate the DNA into the
recipient cell.
•Generaltransduction:any genes can be transferred
•Specializedtransduction:only a few genes can be transferred

15. Bacteriophages have two alternative life cycles:
lytic and lysogenic

16. Multiple Choice Question

17. 1.TheHfrchromosomeistransferredtotheF
—
cellina_____________fashion.
a)circular
b)coiled
c)dimer
d)linear

18. 1.TheHfrchromosomeistransferredtotheF
—
cellina_____________fashion.
a)circular
b)coiled
c)dimer
d)linear
Answer:d

19. 2.WhichofthefollowingistrueforanHfrXF—cross?
a)frequencyofrecombinationhigh,transferofFfactorlow
b)frequencyofrecombinationhigh,transferofFfactorhigh
c)frequencyofrecombinationlow,transferofFfactorhigh
d)frequencyofrecombinationlow,transferofFfactorlow
Answer:a

20. 2.WhichofthefollowingistrueforanHfrXF—cross?
a)frequencyofrecombinationhigh,transferofFfactorlow
b)frequencyofrecombinationhigh,transferofFfactorhigh
c)frequencyofrecombinationlow,transferofFfactorhigh
d)frequencyofrecombinationlow,transferofFfactorlow
Answer:a

21. 3.IntroductionofDNAmoleculesintotherecipientorganismistermedas____________
a)transformation
b)translation
c)transduction
d)transcription
Answer:a

22. 3.IntroductionofDNAmoleculesintotherecipientorganismistermedas____________
a)transformation
b)translation
c)transduction
d)transcription

23. 4.Whichofthefollowingroleisperformedbyabacteriophageintransduction?
a)vector
b)donor
c)recipient
d)episome
Answer:a

24. 4.Whichofthefollowingroleisperformedbyabacteriophageintransduction?
a)vector
b)donor
c)recipient
d)episome

25. Answerkey:
1-d
2-a
3-a
4-a

26. Thank You