Study Guide
Microbiology Principles and Explorations Chapter 8
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University:
Kentucky State University -
Course:
BIO 204 | Fund of Microbiology Academic year:
2024
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Views:
443
Pages:
39
Author:
imophulebf12
Microbiology: Principles and
Explorations
Chapter 8:
Gene Transfer and Genetic
Engineering Types and Significance of Gene Transfer
• Gene transfer: refers to the movement of genetic
information between organisms
• Recombination: The combining of genes (DNA)
from two different cells
• Vertical gene transfer: When genes pass from
parents to offspring
• Horizontal (lateral) gene transfer: Pass genes to
other microbes of their same generation Mechanisms of Lateral Gene Transfer in Bacteria
• Transformation
• Transduction
• Conjugation Transformation
• A change in an organism’s characteristics because of
transfer of genetic information
• Naked DNA: DNA that has been released from an
organism after the cell is lysed and DNA is no longer
incorporated into chromosomes
• Competence factor is released into the medium and
apparently facilitates the entry of DNA into cell
• DNA transport proteins and DNA exonuclease (an
enzyme that cuts up DNA) is also needed The Discovery of Transformation: Griffith’s
experiment with pneumococcal infections in mice The Mechanism of Bacterial Transformation Transduction
• A method of transferring genetic material using a
bacteriophage
• Bacteriophage (phage): a virus that can infect bacteria
• Phages: composed of a core of nucleic acid covered by
protein coat
• Phage capable of infecting a bacterium attaches to a
receptor site on the cell wall • Virulent phage: capable of causing infection and the
destruction and death of a bacterial cell
• Temperate phage: ordinarily does not cause a
disruptive infection
• Prophage: DNA that is incorporated into the host
bacterium’s DNA
• Lysogeny: persistence of a prophage without phage
replication and destruction of bacterial cell Bacteriophage Life Cycles Specialized Transduction
• Several lysogenic phages are known to carry out
specialized transduction
• Lambda phage in Escherichia coli has been studied
• Phages usually insert at a specific location when
they integrate with a chromosome
• Lambda phage inserts into the E. coli chromosome
between the gal gene (galactose) and the bio gene
(biotin) Specialized transduction by lambda phage in Escherichia coli Generalized Transduction
1. Bacteriophage infection of a
host bacterium initiates the
lytic cycle
2. Chromosome is broken into
fragments which can be
picked up and packaged with
phage DNA
3. Particles are released and
infect another bacterial cell
4. Host acquires genes that were
brought along (transduced)
from previous cell The Discovery of Conjugation: Lederberg’s Experiment Conjugation
•
Genetic information is transferred from one cell
to another
•
Conjugation differs from those other
mechanisms in two ways:
It requires contact between donor and recipient
cells
It transfers much larger quantities of DNA
1.
2.
•
Occasionally whole chromosomes can be
transferred TEM of F pili of Escherichia coli The Transfer of F Plasmids
• F plasmids are circular, double-stranded DNA
molecules
• F+ cells contain F (fertility) plasmids and makes
and F pilus
• F- cells lack F plasmids
• F pilus (sex pilus): A conjugation pilus bridge
which it attaches to the F- cell An F+ x F- mating
1. The cell transfers one
strand of DNA from its F
plasmid to the F- cell via
the conjugation bridge
2. The complementary
strands of F plasmid DNA
are synthesized
3. The recipient cell gets a
complete copy of the F
plasmid, and the donor cell
retains a complete copy High-frequency recombinations (Hfr)
• Can induce more than 1000X the number of genetic
recombinations seen in F+ and F• Hfr strains arise from F+ strains when the F plasmid is
incorporated into the bacterial chromosome at one of
several possible sites
• When an Hfr cell serves as a donor in conjugation, the
F plasmid initiates transfer of chromosomal DNA
• Initiating segment: part of the F plasmid is
transferred along with adjacent chromosomal genes High-frequency Recombinations The Transfer of F’ Plasmids
• DNA incorporated into a chromosome can separate
from it and again become an F plasmid
• In some cases this separation occurs imprecisely,
and a fragment of the chromosome is carried with
the F plasmid
• Cells containing such plasmids are called F’ strains The formation and transfer of F’ plasmids Plasmids
1.
2.
3.
4.
5.
6.
F plasmids direct the synthesis of proteins that selfassemble into conjugation pili
Resistance plasmids carry genes that provide
resistance to various antibiotics
Other plasmids direct the synthesis of bacteriocidal
proteins called bacteriocins
Virulence plasmids carry genes that cause disease
Tumor-inducing plasmids cause tumor formation in
plants
Some plasmids contain genes for catabolic enzymes Resistance plasmids These circular pieces of DNA are much smaller than a
bacterial chromosome A typical resistance plasmid can carry genes for resistance
to various antibiotics and to inorganic toxic substances Transposons
• Transposition: the ability of a genetic sequence to
move from one location to another
• Transposable element: a mobile genetic sequence
• Insertion sequence: the simplest type of transposable
element
• Transposon: a transposable element that contains
genes for transposition Transposons: A typical transposon is bounded by
inverted repeat terminals – DNA segments with base
sequences that are identical when read in opposite
directions on different strands Genetic Engineering
• Refers to the purposeful manipulation of genetic material
to alter the characteristics of an organism in a desired
way
• Genetic fusion: allows transposition of genes from one
location on a chromosome to another
• Protoplast fusion: is accomplished by enzymatically
removing the cell walls of organisms of two strains and
mixing the resulting protoplasts Genetic Fusion: A possible example in which the
deletion of a part of a chromosome causes two
different adjacent operons to be joined together Protoplast Fusion Recombinant DNA Technology
•
Making recombinant DNA involves three
processes:
1. Manipulation of DNA in vitro
2. Recombination of another organism’s DNA
with bacterial DNA in a phage or a plasmid
3. The cloning, or production of many
genetically identical progeny, of phages or
plasmids that carry foreign DNA Producing Recombinant DNA Crystals of a
substance toxic to
many insects
Genes for production
of this toxin are
being taken from
Bacillus
thuringiensis Hybridoma
• The fusion of a myeloma (bone marrow cancer
cell) with an antibody-producing white blood cell
• Produces monoclonal antibodies (pure specific
antibodies) A hybridoma cell
Microbiology Principles and Explorations Chapter 8
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