GENETIC
MATTER TRANSFERRING IN BACTERIA
By
Elok M S and Na’afi Aisya
CHAPTER
I
INTRODUCTION
A. Background
Bacteria is one example
of microorganism that learned. Bacteria is group of prokaryote according to the
non-existed of nuclei membrane. Bacteria have a plasmid as a genetic extra
chromosome.
Bacteria as one example
of the microorganisms that live closely related to human life. Often more is
known of the role that bacteria negative role in human life is the transfer
agent of disease. So many human diseases caused by bacteria. Actually, in
addition to the negative role of bacteria cause harm to human life so much positive
role of bacteria.
To determine the role
of bacteria both adverse and beneficial to human life required more knowledge
about bacteria. How is the structure of the constituent bacteria that affect
the role of bacteria for life as well as how the process or mechanism of
bacteria as agents of diseases that can harm human life. Therefore, in this
paper we will discuss transferring the genetic matter that has to do with the
structure of plasmids which are owned by the bacteria, which then affect the
role of bacteria in human life.
B. States
of Problem
a.
How about
the mechanism of genetic transformation in bacteria?
b.
How about
the mechanism of transduction in bacteria?
c.
How about
the mechanism of conjugation in bacteria?
C. Purpose
a.
To know the
mechanism of genetic transformation in bacteria.
b.
To know the
mechanism of transduction in bacteria.
c.
To know the
mechanism of conjugation in bacteria.
CHAPTER
II
CONTENT
A. Genetic
Transformation
A kind of process which free DNA is
incorporated into a recipient cell and brings about genetic change called
genetic transformation. It led to experiments proving without a doubt that DNA
was the genetic material. Both Gram-negative and Gram-positive species are a
number of bacteria that have been found to be transformable.
Competent is a cell that is able to
take up a molecule of DNA and be transformed. Competence in most naturally
transformable bacteria is regulated, and special proteins play a role in the
uptake and processing of DNA. Competence-specific proteins may include a
membrane associated DNA-binding protein, a cell wall autolysin, and various
nucleases. For example in Bacillus, about 20 percent of the cells become
competent and stay that way for several hours whereas in Streptococcus, 100
percent of the cells can become competent just only for a few minutes during
the growth cycle.
Uptake of DNA
The form which DNA is taken up in
bacteria has differences. In gram-negative, only double-stranded DNA is taken
up into the cell despite the fact, only single-stranded segments actually
become incorporated into the genome by recombinant. On the other hand, in
gram-positive, only a single DNA strands is taken up, while the complementary
strand is simultaneously degraded. Actually, the more effectively binds to the
cell is double-stranded DNA.
During the transformation process,
competent bacteria first bind DNA reversibly soon, however the binding becomes
irreversible. Competent cells bind much more DNA than do non-competent cells as
much as 1000 times more. The sizes of the transforming fragments are much
smaller than that of the whole genome and this DNA further degraded during the
uptake process.
Integration of transforming DNA
a.
Transforming
DNA is started by DNA-binding protein which made it bound at the cell surface,
b.
The DNA associates
with a competence-specific protein which remains attached to the DNA,
presumably preventing it from nuclease attack, until it reaches the chromosome
where RecA protein takes over.
c.
The DNA is
integrated into the genome of the recipient by re-combinational process.
d.
During
replication of this hybrid DNA, one parental and one recombinant DNA molecule
is formed.
Upon segregation at cell division, the
letter will be present in the transformed cell, which is now genetically
altered as compared to parental type. The transformation of plasmid DNA
generally occurs in the absence of recombination between the plasmid and
bacterial chromosome.
Electroporation
The cell membranes produce small pores
which exposed to pulsed electrical fields. If DNA molecules are present outside
the cells during the electrical pulse, the can then enter the cells through
these pores. So that, the entering process of DNA molecules to the cells
through the pores by electrical pulse called electroporation.
This technique has now been used to
transport DNA into a large number of different species of bacteria, both
Gram-negative and Gram-positive. Electroporation allows an experimenter to
transfer a plasmid directly from one cell to another if both are present during
electroporation.
B. Transduction
Transduction is a process where DNA is
transferred from cell to cell through the agency of viruses. Genetic transfer
of host genes by viruses can occur in two ways, such as:
a.
Generalized
transduction, host genes derived from virtually any portion of the host genome
become a part of the DNA of the mature virus particle in place of virus genome.
b.
Specialized
transduction, occurs only in some temperate viruses; a specific group of host
genes is integrated directly into the virus genome usually replacing some of
the virus genes and is transferred to the recipient during lysogenization.
Both specialized and generalized
transduction is defective as a virus because bacterial genes have replaced some
necessary viral genes.
a.
Generalized
transduction
Virtually
any genetic marker can be transferred from donor to recipient. Generalized
transduction was first discovered in the bacterium Salmonella typhimurium with phage P22, known occur in Escherichia coli and another bacteria.
(Brock : 2012)
When the
population of sensitive bacteria is infected with a phage, the events of the
phage lytic cycle may be initiated. During a lytic infection, the enzymes
responsible for packaging viral DNA into the bacteriophage sometimes
accidentally package host DNA. The resulting particle is called a transducting particle. Upon lysis of the
cell, these particles are released a long with normal virions, so that the
lysate contains a mixture of normal and transducing virions. Because
transducing particles cannot initiate a normal viral infection (they contain no
viral DNA), they are said to be defective.
When this lysate is used to infect a population of recipient cells, most of the
cells become infected with normal virus. A small proportion of the population
receives transducing particles, whose DNA can now undergo genetic recombination
with the host DNA. Since only a small proportion of the particles in the lysate
are of the defective transducting type and since each of those contains only a
small fragment of donor DNA, the probability of transducting particle
containing a particular gene is quite low.
Phages that
form transducing particles can be either temperate or virulent, the main
requirements being that they have a DNA packaging mechanism that permits
accidental recognition of host DNA and that packaging occurs before the host
genome is completely degraded. The detection of transduction is most certain
when multiplicity of phage to host is low, so that a host cell is infected with
only a single phage particle; with multiple infection, the cell may be killed
by the normal particles.
b.
Specialized
transduction
Specialized transduction is transfer
which efficient process by phage of a specific set of host genes can be
arranged. The example involves transduction of the galactose genes by the
temperate phage lambda of E.coli. When
the cell lysogenized into the host DNA at a specific site, the region in which
lambda integrates is immediately adjacent to the cluster of host genes that
control the enzymes involved in galactose utilization and lambda is inserted
into the host DNA at that site and the replication of viral DNA is under host
control.
(Brock : 2012)
Upon induction, viral DNA separates
from host DNA by process integration reverse. When the lysogenic cell is
induced, lambda DNA is excised as a unit. In rare condition, the phage genome
excised incorrectly. Then both normal and rare conditions are in detached DNA
replication. The phage synthesis occur until its completed. The last the cell
lyses and releases. For the normal condition it occurred with normal phage
whereas the rare condition cell lyses and releases defective phage capable of
transducing galactose genes.
C. Conjugation
Conjugation
is a mechanism of transfer of genetic information (DNA) from donor cell to a
recipient cell that occur as a result of cell-cell contact. Conjugation is
controlled by genes carried by certain plasmids (such as the F plasmid) and involves
transfer of the plasmid from a donor cell to a recipient cell. Plasmid DNA
transfer involves replication via the rolling circle mechanism.
Bacterial
conjugation was first discovered by Lederberg and Tatum in 1946. They combine
the two mutant strains of Escherichia coli distinct unable to synthesize one or
more essential growth factors and give him a chance to mate.
In the
process of conjugation, donor cells (males) included some of the DNA into a
recipient cell via phili sex owned by the male cells. Once the donor DNA into
the recipient cell, enzymes that act on DNA cutting recipient of a DNA fragment
recipient. Then the donor DNA integrated into chromosomal DNA in the recipient.
This mechanism actually takes place also in the activities of transformation
and transduction.
With the
conjugation process, the specific genes for traits such as resistance to the
drug can move from population to population of resistant bacteria resistant
bacteria. Therefore, if it occurs in a population of bacteria can develop
multi-drug resistance.
CHAPTER
III
CONCLUSION
a.
Transduction
is the transfer of host genes from one bacterium to another by a bacterial
virus. In generalized transduction, defective virus particles randomly
incorporate fragments of the cell’s chromosomal DNA, but the transducing
efficiency is low. In specialized transduction, the DNA of a temperate virus
excises incorrectly and takes adjacent host genes along with it; the transducing
efficiency here may be very high.
b.
Transformation
is a genetic transfer process by which free DNA is incorporated into a
recipient cell and brings about genetic change.
c.
Conjugation
is a mechanism of transfer of genetic information (DNA) from donor cell to a
recipient cell that occur as a result of cell-cell contact.
References
Brock, et all. 1994. Biology of Microorganism Seventh Edition.
United States of America : Prentice –Hall International, Inc.
Brock, et all. 2012. Biology of Microorganism Thirteenth Edition
(e-book). San Francisco : Pearson Education, Inc.
Prescott, Lansing M. 2002. Microbiology 5th Edition. USA
: The McGraw−Hill
Companies.
