Transcript Pierce5e_ch09_lecturePPT

Benjamin A. Pierce
GENETICS
A Conceptual Approach
FIFTH EDITION
CHAPTER 9
Bacterial and Viral Genetic Systems
© 2014 W. H. Freeman and Company
When we look at genetic diversity it is very clear that Bacteria and archaea are
more diverse than the diversity see in plants, animals, or fungi. In this chapter
you will come to understand why.
Major Ideas from this chapter.
What kinds of genes are present on plasmids?
How do the processes of Transformation, Transduction, and conjugation
contribute to bacterial diversity.?
How do bacteria contribute to viral diversity?
In cells containing conjugative plasmids ,how do we distinguish between F-,
F+ and Hfr cell types?
9.1 Genetic Analysis of Bacteria Requires
Special Approaches and Methods
• All prokaryotes are unicellular and lack a
membrane-bound nucleus and membranebound organelles
– Eubacteria
– Archaea
• Characteristics of Bacteria
– Diverse shapes and sizes
– Some are photosynthetic
– Replication occur prior to binary fission
9.1 Genetic Analysis of Bacteria Requires
Special Approaches and Methods
• Techniques for the Study of Bacteria
– Prototrophic: wild type
– Auxotrophic: mutant type
– Minimum medium: only required by
prototrophic bacteria
– Complete medium: contain all substances
required by all bacteria, including auxotrophic
bacteria
9.1 Genetic Analysis of Bacteria Requires
Special Approaches and Methods
• The bacterial genome:
– Mostly single, circular DNA
molecule/chromosome (Fig. 9.4)
– Plasmids:
• Extra chromosome, small circular DNA
• Episomes—freely replicating plasmids: F
(fertility) factor
Concept Check 1
Which is true of plasmids?
a. They are composed of RNA.
b. They normally exist outside of bacterial cells.
c. They possess only a single strand of DNA.
d. They replicate independently of the bacterial
chromosome.
Concept Check 1
Which is true of plasmids?
a. They are composed of RNA.
b. They normally exist outside of bacterial cells.
c. They possess only a single strand of DNA.
d. They replicate independently of the bacterial
chromosome.
9.2 Bacteria Exchange Genes Through
Conjugation, Transformation, and
Transduction
Gene Transfer in Bacteria
• Conjugation: direct transfer of DNA from
one bacterium to another
• Transformation: bacterium takes up free
DNA
• Transduction: bacterial viruses take DNA
from one bacterium to another
Concept Check 2
Which process of DNA transfer in
bacteria requires a virus?
a.
b.
c.
d.
Conjugation
Transformation
Transduction
All of the above
Concept Check 2
Which process of DNA transfer in
bacteria requires a virus?
a.
b.
c.
d.
Conjugation
Transformation
Transduction
All of the above
9.2 Bacteria Exchange Genes Through
Conjugation, Transformation, and
Transduction
• Gene Transfer in Bacteria
– Conjugation:
• Direct transfer via connection tube, one-way traffic
from donor cells to recipient cells.
• It is not a reciprocal exchange of genetic
information
9.2 Bacteria Exchange Genes Through
Conjugation, Transformation, and
Transduction
• Gene Transfer in Bacteria
– Conjugation:
• Lederberg and Tatum experiment
• F+ cells: donor cells contain F factor
• F– cells: recipient cells lacking F factor
• Sex pilus: connection tube
9.2 Bacteria Exchange Genes Through
Conjugation, Transformation, and
Transduction
• Gene Transfer in Bacteria
– Conjugation:
• Hfr cells: (high-frequency strains): donor cells with F factor
integrated into the donor bacterial chromosome
• F prime (F) cells: Contains F plasmid carrying some
bacterial genes.
• Merozygotes: partial diploid bacterial cells containing F
plasmid carrying some bacterial genes.
Concept Check 3
Conjugation between an F+ and F− cell usually
results in:
a.
b.
c.
d.
two F+ cells.
two F− cells.
an F+ and an F− cell.
an Hfr and an F+ cell.
Concept Check 3
Conjugation between an F+ and F− cell usually
results in:
a.
b.
c.
d.
two F+ cells.
two F− cells.
an F+ and an F− cell.
an Hfr and an F+ cell.
9.2 Bacteria Exchange Genes Through
Conjugation, Transformation, and
Transduction
• Gene Transfer in Bacteria
– Conjugation:
• Mapping bacterial genes with interrupted
Conjugation:
– Distance between genes are measured by the time
required for DNA transfer from Hfr cells to F– cells. (Fig.
9.15)
• Natural Gene Transfer and Antibiotic Resistance
– Antibiotic resistance comes from the actions of genes
located on R plasmids that can be transferred naturally.
9.2 Bacteria Exchange Genes Through
Conjugation, Transformation, and
Transduction
• Gene Transfer in Bacteria
– Conjugation:
• Natural Gene Transfer and Antibiotic Resistance
– Antibiotic resistance comes from the actions of genes
located on R plasmids that can be transferred naturally.
– R plasmids have evolved in the past 60 years since the
beginning of widespread use of antibiotics.
– The transfer of R plasmids is not restricted to bacteria of
the same or even related species.
9.2 Bacteria Exchange Genes Through
Conjugation, Transformation, and
Transduction
• Transformation:
– A bacterium takes up DNA from the medium.
– Recombination takes place between
introduced genes and the bacterial
chromosome.
9.2 Bacteria Exchange Genes Through
Conjugation, Transformation, and
Transduction
• Transformation:
– Competent cells: cells take up DNA
– Transformants: cells that receive genetic
material
– Cotransformed: cells that are transformed by
two or more genes
9.2 Bacteria Exchange Genes Through
Conjugation, Transformation, and
Transduction
• Bacterial Genome Sequences:
– ~ 1-4 million base pairs of DNA
• Horizontal Gene Transfer:
– Genes can be passed between individual members of
different species by nonreproductive mechanisms.
9.3 Viruses Are Simple Replicating
Systems Amenable to Genetic Analysis
• Virus: Replicating structure (DNA/RNA) +
Protein coat.
• Bacteriophage: bacterial infection virus
– Virulent phages: reproduce through the lytic cycle,
and always kill the host cells.
– Temperate phages: inactive prophage—phage DNA
integrates into bacterial chromosome.
9.3 Viruses Are Simple Replicating
Systems Amenable to Genetic Analysis
• Transduction:
– Bacterial viruses (bacteriophage) carries DNA
from one bacterium to another.
– Transduction usually occurs between bacteria
of the same or closely related species.
Concept Check 4
In gene mapping experiments using generalized
transduction, bacterial genes that are
cotransduced are:
a.
b.
c.
d.
far apart on the bacterial chromosome.
on different bacterial chromosomes.
close together on the bacterial chromosome.
on a plasmid.
Concept Check 4
In gene mapping experiments using generalized
transduction, bacterial genes that are
cotransduced are:
a.
b.
c.
d.
far apart on the bacterial chromosome.
close together on the bacterial chromosome.
on different bacterial chromosomes.
on a plasmid.
9.3 Viruses Are Simple Replicating
Systems Amenable to Genetic Analysis
• RNA Virus
– Retrovirus: RNA viruses that have been
integrated into the host genome.
• Reverse Transcriptase: synthesizing DNA from
RNA or DNA template.
– HIV and AIDS
Influenza
• Rapid changes occur through genetic
recombination
• Three main types: influenza A, influenza
B, and influenza C
• Most cases influenza A: divided into
subtypes based upon expression of
hemagglutinin (HA) and neuraminidase
(NA)