Microbial Models: The Genetics of Bacteria and Viruses

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Microbial Models The Genetics of Bacteria and
Viruses

• Chapter 18

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Figure 1.  Typical mosaic pattern on flue-cured
tobacco leaves infected with Tobacco mosaic
virus. (Courtesy H.D. Shew)
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LE 18-2
Virus
Bacterium
Animal cell
Animal cell nucleus
0.25 µm
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LE 18-4
Capsomere of capsid
Membranous envelope
RNA
Capsomere
Capsid
DNA
Head
RNA
DNA
Tail sheath
Tail fiber
Glycoprotein
Glycoprotein
7090 nm (diameter)
80200 nm (diameter)
18 ? 250 mm
80 ? 225 nm
50 nm
50 nm
50 nm
20 nm
Tobacco mosaic virus
Adenoviruses
Influenza viruses
Bacteriophage T4
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LE 18-5
VIRUS
Entry into cell and uncoating of DNA
DNA
Capsid
Transcription
Replication
HOST CELL
Viral DNA
mRNA
Viral DNA
Capsid proteins
Self-assembly of new virus particles and their
exit from cell
Activity Viral Reproductive Cycle
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LE 18-6
Lytic Cycle
Attachment
Entry of phage DNA and degradation of host DNA
Phage assembly
Release
Head
Tails
Tail fibers
Synthesis of viral genomes and proteins
Assembly
Activity Lytic Cycle
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LE 18-7
Phage DNA
The phage attaches to a host cell and injects its
DNA.
Daughter cell with prophage
Many cell divisions produce a large population
of bacteria infected with the prophage.
Phage DNA circularizes
Phage
Bacterial chromosome
Occasionally, a prophage exits the bacterial
chromosome, initiating a lytic cycle.
Lytic cycle
Lysogenic cycle
Certain factors determine whether
The bacterium reproduces normally, copying the
prophage and transmitting it to daughter cells.
The cell lyses, releasing phages.
Lytic cycle is induced
Lysogenic cycle is entered
or
Prophage
Phage DNA integrates into the bacterial
chromosomes, becoming a prophage.
New phage DNA and proteins are synthesized and
assembled into phages.
Activity Lytic Lysogenic Cycle
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Class/Family Envelope Examples/Disease
I. Double-stranded DNA (dsDNA) I. Double-stranded DNA (dsDNA) I. Double-stranded DNA (dsDNA)
Adenovirus No Respiratory diseases, animal tumors
Papovavirus No Papillomavirus (warts, cervical cancer) polyomavirus (animal tumors)
Herpesvirus Yes Herpes simplex I and II (cold sores, genital sores) varicella zoster (shingles, chicken pox) Epstein-Barr virus (mononucleosis, Burkitts lymphoma)
Poxvirus Yes Smallpox virus, cowpox virus
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Class/Family Envelope Examples/Disease
II. Single-stranded DNA (ssDNA) II. Single-stranded DNA (ssDNA) II. Single-stranded DNA (ssDNA)
Parvovirus No B19 parvovirus (mild rash)
III. Double-stranded RNA (dsRNA) III. Double-stranded RNA (dsRNA) III. Double-stranded RNA (dsRNA)
Reovirus No Rotavirus (diarrhea), Colorado tick fever virus
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Class/Family Envelope Examples/Disease
IV. Single-stranded RNA (ssRNA) serves as mRNA IV. Single-stranded RNA (ssRNA) serves as mRNA IV. Single-stranded RNA (ssRNA) serves as mRNA
Picornavirus No Rhinovirus (common cold) poliovirus, hepatitis A virus, and other enteric (intestinal) viruses
Coronavirus Yes Severe acute respiratory syndrome (SARS)
Flavivirus Yes Yellow fever virus, West Nile virus, hepatitis C virus
Togavirus Yes Rubella virus, equine encephalitis viruses
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Class/Family Envelope Examples/Disease
V. ssRNA template for mRNA synthesis V. ssRNA template for mRNA synthesis V. ssRNA template for mRNA synthesis
Filovirus Yes Ebola virus (hemorrhagic fever)
Orthomyxovirus Yes Influenza virus
Paramyxovirus Yes Measles virus mumps virus
Rhabdovirus Yes Rabies virus
VI. ssRNA template for DNA synthesis VI. ssRNA template for DNA synthesis VI. ssRNA template for DNA synthesis
Retrovirus Yes HIV (AIDS) RNA tumor viruses (leukemia)
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Figure 18.9 Viral infection of plants
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Figure 18-12
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LE 18-13
PRIONS infectious proteins which cause
degenerative brain diseases
(like mad cow disease) most likely transmitted
in food
Original prion
Prion
Many prions
New prion
Normal protein
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LE 18-14
Replication fork
Origin of replication
Termination of replication
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Figure 18.x7 E. coli
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Figure 18.x8 E. coli dividing
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Figure 18.x10 Plasmids
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Figure 18.12 Detecting genetic recombination in
bacteria
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Figure 18.13 Transduction (Layer 4)
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LE 18-17
Sex pilus
5 µm
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Figure 18.15 Conjugation and recombination in E.
coli (Layer 4)
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Figure 18.16 Insertion sequences, the simplest
transposons
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Figure 18.17 Insertion of a transposon and
creation of direct repeats
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LE 18-19
Insertion sequence
5
3
3
5
Inverted repeat
Inverted repeat
Transposase gene
Transposon
Insertion sequence
Insertion sequence
Antibiotic resistance gene
5
3
3
5
Transposase gene
Inverted repeat
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Figure 18.18 Anatomy of a composite transposon
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LE 18-20
Regulation of enzyme production
Regulation of enzyme activity
Precursor
Feedback inhibition
Enzyme 1
Gene 1
Enzyme 2
Gene 2
Regulation of gene expression
Gene 3
Enzyme 3
Enzyme 4
Gene 4
Gene 5
Enzyme 5
Tryptophan
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LE 18-21a
trp operon
Promoter
Promoter
Genes of operon
DNA
trpE
trpC
trpB
trpA
trpR
trpD
Operator
Stop codon
RNA polymerase
Regulatory gene
Start codon
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mRNA 5
mRNA
5
D
B
E
C
A
Protein
Inactive repressor
Polypeptides that make up enzymes for tryptophan
synthesis
Tryptophan absent, repressor inactive, operon on
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LE 18-21b_1
DNA
mRNA
Protein
Active repressor
Tryptophan (corepressor)
Tryptophan present, repressor active, operon off
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LE 18-21b_2
DNA
No RNA made
mRNA
Protein
Active repressor
Tryptophan (corepressor)
Tryptophan present, repressor active, operon off
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LE 18-22a
Promoter
Regulatory gene
Operator
lacl
lacZ
DNA
No RNA made
3
mRNA
RNA polymerase
5
Active repressor
Protein
Lactose absent, repressor active, operon off
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LE 18-22b
lac operon
DNA
lacl
lacZ
lacY
lacA
RNA polymerase
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mRNA
mRNA 5
5
Permease
Transacetylase
?-Galactosidase
Protein
Inactive repressor
Allolactose (inducer)
Lactose present, repressor inactive, operon on
Activity lac Operon
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LE 18-23
Promoter
DNA
lacl
lacZ
RNA polymerase can bind and transcribe
Operator
CAP-binding site
Active CAP
cAMP
Inactive lac repressor
Inactive CAP
Lactose present, glucose scarce (cAMP level
high) abundant lac mRNA synthesized
Promoter
DNA
lacl
lacZ
CAP-binding site
Operator
RNA polymerase cant bind
Inactive CAP
Inactive lac repressor
Lactose present, glucose present (cAMP level
low) little lac mRNA synthesized
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Figure 18.x6 Herpes
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Figure 18.x1 Smallpox
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Figure 18.x3 Polio
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LE 18-8
Capsid
Capsid and viral genome enter cell
RNA
HOST CELL
Envelope (with glycoproteins)
Viral genome (RNA)
Template
mRNA
Capsid proteins
ER
Glyco- proteins
Copy of genome (RNA)
New virus
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LE 18-11
The SARS-causing agent is a coronarvirus like
this one (colorized TEM), so named for the
corona of glyco-protein spikes protruding form
the envelope.
Young ballet students in Hong Kong wear face
masks to protect themselves from the virus
causing SARS.
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Figure 18.x4 Hepatitis
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Figure 18.x5 Influenza epidemic
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Figure 18.x2 Measles
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LE 18-9
Viral envelope
Glycoprotein
Capsid
RNA (two identical strands)
Reverse transcriptase
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LE 18-10
Membrane of white blood cell
HIV
HOST CELL
Reverse transcription
Viral RNA
RNA-DNA hybrid
0.25 µm
HIV entering a cell
DNA
NUCLEUS
Provirus
Chromosomal DNA
RNA genome for the next viral generation
mRNA
Activity HIV Reproductive Cycle
New HIV leaving a cell
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Figure 18.7x1 HIV infection