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Viral Structure and Function - Coggle Diagram
Viral Structure and Function
Characteristics/History
1886, Adolf Mayer= TMD- tobacco mosaic disease, transmitted from affected plant to healthy plant
1892, Dimitri Iwanoski filtered sap of infected plants and found the fluid was able to transmit the disease- "filterable agent" (used porcelain filter)
DO NOT have plasma membrane, reproduce by binary fission and cannot make own ATP. Sensitive to interferon (bacteria are sensitive to antibiotics)
first human disease associated with filterable agent was yellow virus "yellow jack", also first disease shown to be caused by a virus
Contain nucleic acid (RNA/DNA), protein coat. Some may possess an envelope
1901, Walter Reed, showed that yellow fever was the first to be transmitted by a mosquito (vector)
Viruses= obligatory intracellular parasite, small enough to pass through 0.2 u filters (filterable agents of disease)
1930, Wendell Stanley, isolated the TMD and the electron microscope was invented
Viral structure and genetics
spikes= carbohydrate and protein complexes that project from the capsid/envelope surface. In influenza virus, spikes are used to clump RBC's together= hemagglutination
4 main types of viral genetic material and examples are (nucleic acid):
Nonenveloped virus consists only of the nucleic acid and capsid
ssDNA (few): Parvoviridae (parvovirus)
Envelope may be present around the outside of the capsid. consists of part of hose cell membrane along with proteins coded for by the virus
dsDNA (many): Herpesviridaw (simplexvirus)
Protein coat surrounding the nucleic acid core= capsid, composed of subunits called capsomeres
Virion= complete, fully developed, infectious viral particle composed of nucleic acid and protein coat
+ssRNA (many): Picornaviridae (polio, rhinovirus)
dsRNA (few): Reoviridaw (rotavirus)- gastroenteritis
Viral Morphology
Polyhedral virus- often icosahedron (20 equilateral triangles) such as Poliovirus or Adenovirus
Helical Virus- filovirus (ebola) and Rhabdoviridae (rabies)
Enveloped Icosahedral virus- Herpesviridae (causing cold sores and chicken pox/shingles
Complex viruses- characterized by being dsDNA, enveloped and very large (T-bacteriophage)
most viruses are species specific, few have a broad host range
Bacteriophages infect only attachment sites on bacterial hosts, these include cell wall, fimbriae or flagella
Receptor sites for animal viruses are proteins and glycoproteins of the plasma membrane of the host cell
viral replication
Lytic Cycle (T4 phage, virulent phage) ends in death of the host cell
Lysogenic Cycle (Lambda phage, a temperate phage) involves insertion of phage DNA into the host genome, forming a prophage. Phage remains latent and host cell remains lysogenic
most animal DNA viruses, DNA replication occurs in nucleus of the host cell, the exception is pox viruses where components are synthesized in cytoplasm
Significant result of lysogen is phage conversion- host cell may exhibit new properties (Corynebacterium diphtheria) producing the disease only when a prophage is present that code for the cytotoxin
multiplication of animal virus, entry occurs by pinocytosis or fusion (for enveloped viruses). Unocating involves digestion of protein coat, often by lysosomal enzymes
Yellow Fever
Sylvatic cycle= mosquitoes transmitting the disease from monkey > monkey and monkey > human
Urban Cycle= Aedes aegypti mosquitoes transmitting the disease from human > human
caused by Flavivirus (ssRNA, envelope) zoonotic disease
Prevention= vacine (attenuated yellow fever 17D strain) and mosquito control
Influenza
Influenza is spread by aerosol transmission
TMT: annual vaccinations (prevent uncoating) N spike inhibitors- decrease length of disease by 3 days
N spikes (neuraminidase) help virus seperate from infected cells after replication and infect a new cell
capsid: protein coat, envelope: lipid bilayer
H spikes (hemagglutinin) allow virus to attach to specific host cell receptors (our antibodies go against H spike)
Family: Orthomyxoviridae, has a genome composed of 8 seperate RNA segments
Antigenic shift
Caused by major genetic recombination Ex: mixing of RNA segments= major change in H/N portions and cause antibodies formed against one strain that are not productive following a antigenic shift
Antigenic Drift
reflects minor annual vaccinations in the antigen makeup of the influenza virus. alteration of spring a.a. of H/N spike. Vaccines slightly different each year to accommodate antigenic shift/drift
Latent viral
infections that are often activated by stress and may not recur for months to years. ex: cold sores and shingles, caused by human herpes virus
Retro viruses
carry enzyme: reverse transcriptase- use viral RNA as a template to produce complementary double-stranded DNA. this viral DNA can be inserted into a host cell chromosome as a provirus. Provirus can remain in a latent stage and replicate with the host DNA