Chapter18 Microbial Models The genetics of Virus and Bacteria

The Genetics of Virus  Researchers discovered virus by studying a plant disease  A virus is a genome enclosed in a protective coat  Phage reproduces using lytic or lysogenic cycle  Animal virus are diverse in their modes of infection and reproduction  Plant virus are serious agriculture pests  Viroid and prion are infectious agent even simpler than virus  Viruses may have evolved from other mobile genetics elements

Figure 18.1 Comparing the size of a virus, a bacterium, and a eukaryotic cell

1883 Adolph Mayer Tobacco Mosaic Virus-- contagious 1890 Dimitri Ivanowsky Bacteria makes filterable toxins 1897 Martinus Beijerinck Infectious agent in the filtered sap could reproduce and cannot inactivate by alcohol 1933 Wendall Stanley Crystallized the TMV particle

Figure 18.9x Tobacco mosaic virus Rod shape > 1000 molecules

Figure 18.02x1 Adenovirus  Infect respiratory tract  252 identical protein  polyhedral

Capsid Protein shell that encloses the viral genome Capsomere Capsid build from a large number of protein subunit Viral envelope Membrane cloaking the capsid, derived from host cell

Figure 18.3 A simplified viral reproductive cycle  Limited host range  Identify host by lock-and-key  Virus of eukaryotic are tissue specific  Uses host DNA polymerase to synthesize genome

Lytic cycle A phage reproductive cycle that culminate in death of host cell, bacteria lyse, phages release

Figure 18.4 The lytic cycle of phage T4

Figure 18.5 The lysogenic and lytic reproductive cycles of phage, a temperate phage

Figure 18.02x2 Phages

Table 18.1 Classes of Animal Viruses, Grouped by Type of Nucleic Acid

Figure 18.6 The reproductive cycle of an enveloped virus

Figure 18.7 HIV, a retrovirus

Three process for emergence of viral disease: 1.Mutation of existing virus i.e.. High mutation of RNA virus flu virus 2. Spreading existing virus from one host to another i.e.. SARS, Hanta virus 3. Dissemination of viral disease from a small isolated population I.e. AIDS

Figure 18.7x1 HIV infection

Figure 18.7x2 Couple at AIDS quilt

Figure 18.x1 Smallpox

Figure 18.x2 Measles

Figure 18.x3 Polio

Figure 18.x4 Hepatitis

Figure 18.x5 Influenza epidemic

Figure 18.8 Emerging viruses Ebola virus Hemorrhagic fever

Figure 18.8x Deer Mouse Hanta virus

Figure 18.x6 Herpes

Plant virus mostly are RNA virus Two major route to spread virus: 1.Horizintal transmission a plant infect from external source of the virus I.e wind, chilling, injury, insects bite……… 2. Vertical transmission inherit the viral infection from a parent

Figure 18.9 Viral infection of plants

Viroid Naked circular RNA Replicate by using host enzyme Cause error in regulatory system and control plant growth

Figure A hypothesis to explain how prions propagate 1997 Stanley Prusiner Prion Infectious protein Mad cow disease; degenerative in brain

Virus may have evolved from mobile genetic elements 1.Plasmids Circular DNA separate from genome 2. Transposon DNA fragments that move from one location to another

The Genetics of Bacteria  The short generation span of bacteria helps them adapt to changing environments  Genetic recombination produces new bacterial strain  The control of gene expression enables individual bacterial to adjust their metabolism to environmental change

Bacterial genome d.s circular DNA DNA localized in the nucleoid region Divide by binary fission

Figure Replication of the bacterial chromosome

Figure 18.x7 E. coli

Figure 18.x8 E. coli dividing

Figure 18.x9 Bacterium releasing DNA with plasmids

Figure 18.x10 Plasmids Plasmids Small circular, self replicating DNA

Figure Detecting genetic recombination in bacteria

Different process bring bacterial DNA from different individuals: 1.Transformation uptake of naked, foreign DNA from surrounding i.e. uptake of pathogenic pneumonia DNA from broken bacteria pieces 2. Transduction DNA transfer process by bacterial phage

Figure Transduction (Layer 1)

Figure Transduction (Layer 2)

Figure Transduction (Layer 3)

Figure Transduction (Layer 4)

3. Conjugation Direct transfre of genetic materials between two bacterial donar: male receiver: female

Figure Bacterial mating

Plasmids  Small circular, self replicating DNA  Incorporate reversible into bacterial genome  Episome exist as plasmids or in bacteria genome

F plasmid Required for sex pili Hfr cells( high frequency of recombination) F factor integrate into bacterial chromosome R plasmid Plasmids carrying antibiotic resistance gene

Figure Conjugation and recombination in E. coli

Transposon( jumping gene) A transposable genetic element Movement occur only when recombination of transposon and target site occur

Figure Insertion sequences, the simplest transposons

Figure Insertion of a transposon and creation of direct repeats

Figure Anatomy of a composite transposon  Include extra genes beside insertion sequence  Helps bacterial adapt to the new environment

Figure Regulation of a metabolic pathway

Figure 18.20a The trp operon: regulated synthesis of repressible enzymes

Figure 18.20b The trp operon: regulated synthesis of repressible enzymes (Layer 1)

Figure 18.21a The lac operon: regulated synthesis of inducible enzymes

Figure 18.21b The lac operon: regulated synthesis of inducible enzymes

Figure 18.22a Positive control: cAMP receptor protein

Figure 18.22b Positive control: cAMP receptor protein

Figure 18-22x cAMP

Bacterial and viral growth curves

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