Download Genetics

Batterjee Medical College
Batterjee Medical College
Bacteria Genetics
Ass. Prof. Dr. Manal El Said
Head of Microbiology Department
Batterjee Medical College
Bacteria Genetics
• Bacteria have only one copy of
their genome DNA, i.e., they are
haploid.
• Eukaryotic cells have two copies of
their genome DNA, i.e., they are
diploid.
• Bacterial DNA is circular; human
nuclear DNA is linear.
Batterjee Medical College
Transfer of DNA Within
Bacterial Cells
Transposons
• Transposons are small pieces of DNA that move readily
from one site on bacterial chromosome to another or from
bacterial chromosome to plasmid.
• They carry antibiotic resistance genes.
• Transfer of transposons on plasmids to other bacteria by
conjugation contributes to antibiotic resistance.
Batterjee Medical College
Transfer of DNA Within
Bacterial Cells
Programmed rearrangements: are movement of genes from
inactive ( storage) sites into active sites where they are
expressed as new proteins.
• Bacteria can acquire new proteins (antigens) on their
surface and evade the immune system e.g. Neisseria
gonorrhoeae & Trypanosoma brucei
Batterjee Medical College
Transfer of DNA between
Bacterial Cells
The transfer of genetic information from one cell to another
can occur by
Conjugation
Transduction Transformation
Batterjee Medical College
Transfer of DNA between
Bacterial Cells: Conjugation
• Conjugation:
DNA
(plasmid
carrying antibiotic resistance
gene
or
chromosomal)
is
transferred from one bacterium to
another.
• Donor bacterium have "fertility"
plasmid (F plasmid).
• Pilin protein forms sex pilus
(conjugation tube).
• DNA transferred by conjugation
to recipient bacterium is a new
copy that allows donor to keep a
copy of DNA.
Batterjee Medical College
Transfer of DNA between
Bacterial Cells: Transduction
• It is process by which DNA
(plasmid or chromosomal) is
transferred from one bacterium
to another by virus.
• Transferred DNA integrates into
chromosomal DNA of recipient
&
new
proteins,
such
as
exotoxins, are made- a process
called lysogenic conversion.
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Transfer of DNA between
Bacterial Cells: Transformation
Transformation is the process by which DNA itself, either
DNA released from dying cells or DNA purified in the
laboratory, enters a recipient bacterium.
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Transfer of DNA between
Bacterial Cells
Comparison of Conjugation, Transduction & Transformation
Transfer
Process
Procedure
Conjugation
Type of Cells
Nature of DNA Transferred
Involved
DNA transferred
Prokaryotic
from one bacterium
- Chromosomal
- plasmid
to another
Transduction
DNA transferred by
Prokaryotic
virus from one cell
-Generalized transduction:
Any gene
to another
-Specialized transduction:
Only certain genes
Transformation
Purified DNA taken
-Prokaryotic
up by a cell
-Eukaryotic
Any DNA