Transcript Acellular Microbes

Acellular Microbes
Infectious Agents
Viruses
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Range from 10-300 nm.
academic.pgcc.edu/.../Chapter%2013/size.html
All Organisms Have the Potential to be
Infected by Some Type of Virus.
Tobacco Mosaic Virus.
www.ncbi.nlm.nih.gov/.../Milne/tob
amo1.htm
Small pox
virus.
www.ncbi.nlm.n
ih.gov/ICTVdb/I
mages/Murphy/
Dow..
E. Coli being attacked
by lambda
bacteriophage.
www.asm.org/division/m/foto/
LamAttack.html
Leaf left = uninfected
tobacco leaf. Right
leaf = infected leaf.
www.nature.com/.../v411/n68
39/full/411848a0.html
Man infected with
small pox.
www.idph.state.il.us/Bioterror
ism/spoxphoto1.htm
Sooooo……….
what is a virus?
Virus Characteristics
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1. Have genetic material, either DNA or RNA.
2. Can’t replicate without a host cell.
3. Can’t divide by binary fission, mitosis, or
meiosis.
4. Can’t make their own energy (steal it from host
cell).
5. Can’t make their own protein or genetic
material (steal from host cell).
Characteristics of a Typical Virus
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1. Consists of a genome of either RNA or
DNA.
 2. Genetic material surrounded by a capsid
or protein coat.
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Composed of small protein units called capsomeres.
3. Some viruses have an outer envelope.
 4. May also have a tail, sheath, and tail
fibers.
A Typical Virus
Virus Classification
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Type of genetic material.
Shape of the capsid.
Number of capsomeres.
Size of the capsid.
Presence or absence of an envelope.
Type of host it infects.
Type of disease it produces.
Target cell.
Immunologic or antigenic properties.
Viral Classification
www.biotech100.com
www.antibac2k.com
Where did
viruses come from?
Virus Origin
3
Major Theories
1. Viruses are remnants of past infections
(e.g. mitochondrion/chloroplasts).
 2. Cells came before viruses.
• Viruses are degenerate cells or cell
fragments.
 3. Viruses represent a separate
evolutionary branch
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What if. . . .
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Scientists found a cell that was as large or
larger than some bacteria and that cell had
the capabilities to produce almost
everything it needed to “live.”
 It required a host cell only to make some
ribosomes.
 Is it a virus or a living cell?
Meet Mimi!
http://www.microbiologybytes.com/virology/Mimivirus.html
Retrovirus
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Genetic information is
single-stranded RNA.
 Have a special enzyme
called reverse
transcriptase.
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This enzyme makes
DNA from RNA.
Integrate their newly
formed doublestranded DNA into the
host cell.
 Example = HIV
Human Immunodeficiency
Virus (www.msu.edu)
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Many
“Junk DNA”
retroviruses
are
responsible for
“junk DNA”
in our
genome.
Illustration by James Collins
(www.rps.psu.edu )
Sheep, Viruses, and Dr. Spencer
Bacteriophage
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A virus that infects bacteria.
 2 types
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1. Virulent Bacteriophage
2. Temperate Bacteriophage
Virulent Bacteriophage
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Causes Lytic Cycle
(5 steps)
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1. Attachment
2. Penetration
3. Biosynthesis
4. Assembly
5. Release
oceanworld.tamu.edu
textbookofbacteriology.net
Temperate Bacteriophage
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Do not immediately begin lytic cycle.
 Their DNA remains embedded in bacterial
cell chromosome.
Animal Viruses
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Species specific.
Attach to specific binding
sites on cells.
This affects what species
and which cell type is
infected.
Multiplication of Animal
Viruses (6 steps)
– 1. Attachment
– 2. Penetration
– 3. Uncoating
– 4. Biosynthesis
– 5. Assembly
– 6. Release
www.heritageparkzoo.org
Budding
A transmission electron
microscopy (TEM) image of
influenza viruses budding from
the surface of an infected cell.
(CNRI/Science Photo Library, National Audubon
Society Collection/Photo Researchers, Inc.)
Antiviral Agents
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Interfere with the
phases of viral
multiplication.
 May disrupt a binding
site.
 May disrupt an enzyme
or protein.
 May interfere with the
synthesis of viral parts
like DNA, RNA, or
protein synthesis.
Oncogenic Viruses
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Viruses that cause
cancer.
 Ex. Human
papillomaviruses
(HPV – wart viruses)
cause different types
of cancers.
– i.e. cervical cancer
and other types of
cancers of the genital
tract.
Kaposi Sarcoma – caused by human
herpesvirus 8.
www.hyle.org
Plant Viruses
Maize chlorotic mottle virus (MCMV)
nu-distance.unl.edu
Viroids and Prions
Viroids
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Consist of short,
fragments of singlestranded RNA.
 Only found in plants
(so far).
 Can interfere with
plant’s metabolism,
resulting in the plant
being stunted or
killed.
 Ex. Potato spindle
tuber
Left: normal potatoes; Right –
infected potatoes
www.unece.org
Proteins
Left = unfolded protein; Right = folded protein
Prions
Left = correct protein folding; Right = wrong protein folding
www.cogs.susx.ac.uk
Prions
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Small infectious proteins.
 Cause fatal neurologic diseases in animals.
 Cause fatal spongiform encephalopathies.
– Brain becomes riddled with holes.
Brain with spongiform encephalopathy
webs.wichita.edu
Prion Animal Infections
Sheep infected with
scrapie. (www.gov.mb.ca)
Deer infected with
“chronic wasting disease.”
(http://www.fw.delaware.gov)
Bovine spongiform
encephalopathy, “mad
cow disease.”
Prion Human Infections
Kuru infected boy.
Papua, New Guinea.
Creutzfeldt-Jakob
disease. www.nlm.nih.gov
pathology.mc.duke.edu
Fatal familial insomnia
The End