Download Virus-like particles (read pages 365

Virus-like particles (read pages 365-366).
Viroids and Prions (see virus lec. for discussion of prions)
Viroids -
are common plant pathogens and an emerging economic problem.
They are the smallest known pathogens…..small
naked, ss RNA
Viroids
25 different viroid sequences have been determined and numerous variants
identified.
Avsunviroidae:e.g. avocado sunblotch viroid, peach latent mosaic
Pospiviroidae:
Subgroup 1: potato spindle tuber viroid, coconut cadang cadang viroid, tomato
plant macho viroid
Subgroup 2:citrus bent leaf viroid, pear blister canker viroid
(< 400 nucleotides; the smallest virus is 10x bigger).
• They are all single stranded covalent circles
• There is extensive intramolecular base pairing (see next slide)
The structure of a viroid is shown below:
- lack a protein or membrane coat.
- cause some plant diseases, e.g. potato spindle
disease and Cadang disease of coconuts.
Exactly how viroids cause disease is not
understood - they don’t contain protein encoding genes.
Viroids are replicated in plant cell nuclei by RNA polymerases.
The seem to act like “regulatory RNAs” in plants and cause
severe stunting and often death
Structure of a viroid, showing how a circular single
stranded RNA (246-399 nucleotides) can form a
seemingly double-stranded structure……..
The Potato Spindle Tuber Viroid (PSTV) was the first
viroid discovered (by T.O. Diener in 1971). This is a
very serious disease of potatoes and can be spread by
contaminated tools or through pollen and seeds and
can infect eggplants and tomatoes as well as
potatoes….
Normal potato
Viroids are replicated in plant cell nuclei by
RNA polymerases. The seem to act like
“regulatory RNAs” in plants and cause severe
stunting and often death
PSTV infected potato
Some excerpts from Sandra Sonada’s lecture…..
Virulence Factors of Pathogens
• Four categories
–
–
–
–
Colonization of surface, followed by
toxin production
• V. cholera
– Toxin activates host epithelial trans-membrane pump to cause Clefflux, with H2O following
– Up to 15-20L fluid loss; if 7% loss of body wt, requires IV fluids
• B. pertussis (whooping cough)
– Attach to ciliated epith, toxin causes release of NO fm goblet cells
– Kills ciliated epithelial cells
Toxins
Adhesion Factors
Evasive Factors
Invasive Factors
Establishment of infection
• Adherence
• Colonization
• Delivery of effector molecule
Adherence
Adherence
• Adhesins – located on tips of pili or is component of
glycocalyx or cell walls
– Generally, glycoproteins or glycolipids
– Binding is specific
• Ex: E. coli c plasmid encoding other adhesins allow adherence to
bladder epithelial cells
• Hemagglutinins (remember flu lecture) on viruses that
recognize receptors on cells in upper respiratory tract
– Typing makes up part of categorizing flu strains
Figure 19.3
Self molecule mimicry:
Penetration of skin
• Trauma
– Deep wounds for C. tetani
• Arthropods
– West Nile Virus, Yellow Fever
- mosquitoes
S. pyogenes – capsule composed of hyaluronic
acid
• Hyaluronic acid – polysacch found in
host tissues.
Damage to the host
• Exotoxins
• Endotoxins
Exotoxins
A-B toxin,
as in
diphtheria
Figure 19.12
Endotoxins – G -, Lipid A
Endotoxin – Lipid A
• Do not contain proteins, not actively
released from bacteria during growth, have
no enzymatic activity
• Sm amt = potent activator of physiologic
responses
• Recognized by phagocytes, which then
secrete cytokines – results in physiologic
response
Figure 19.14
MICROBIOLOGY - EBIO 3400 - Practice Questions 3
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
b. unmethylated.
a. are rare on the skin, but more abundant deep in the nose.
c. heart and lungs
c. invading cells are coated and therefore marked for destruction.
c. destroyed by the complement system and/or phagocytes.
e. all of the above
b. lipid / polysaccharide
b. antigens
c. give harmless bacteria a head start in colonizing mucosal surfaces in areas such as the colon.
b. lysogenic (= temperate phage)
e. a and b.
b. electroporation.
__A___uptake of naked DNA
___B__transfer of DNA by cell to cell contact
____C_transfer of DNA by viruses
Briefly describe the reservoir(s), vector and pathogen (Genus species) involved in epidemics of
______ (insert any disease we have discussed into blank). (50 words or less)
Plague is caused by the Gram- bacterium Yersinia pestis. The reservoirs for plague are wild rodents such
as rats and prairie dogs. Fleas from the rodents are the vectors for the disease. Pneumonic plague
can also be spread through the air or direct contact.
15. Briefly discuss why the incidence of West Nile Virus in Colorado dropped
dramatically in 2004 compared to 2003. (50 words or less)
Because the West Nile Virus isn’t passed from generation to generation of mosquito and the
reservoir (birds) for the disease either die or become immune to the virus and clear it from
their bodies (and therefore are no longer reservoirs).