Viruses
List organisms that are host to viruses
Al of them
Anima viruses use nucleus acid types
All 4
Attachment
All viruses except plant viruses must attach to a potential host cell long enough to gain entry Attachment is accomplished by specific interactions between molecules on the surface of the virions (ligand) and molecules on surface of host cell called receptors
Pox virus virions
Among largest of animal viruses Seen with light microscope Complex internal structure with an ovoid to brick shaped exterior
General pattern of viral replicative cycles
Attachment/absorption Entry Synthesis Assembly Release
Vaccinia virus
Double stranded DNA genome associated with proteins and contained in the core Central structure shaped like bacon Ave disc surrounded by membrane Two lateral bodies between core and outer envelope
One step growth curve
Eclipse- virus is intracellular and can't be detected, in latent period Latent period- no virions released Rise period- rapid release of infective phages Plateau- no more virions produced
Large bacteriophages
Elaborate virions T2, T4, T6 phages (T-even) that infect E coli Have Binal symmetry because head that is icosahedral and helical tail
Progress studying virions has come from
Electron microscopy X ray diffraction Biochemical analysis Immunology
Rabies virus
Envelope firmly attached to underlying nucleocapsid and endow the virion with a constant characteristic bullet shape
Budding is frequently observed in
Enveloped viruses Envelope formation and virion release normally a concurrent process
Viruses intracellularly
Exist primarily as nucleic acids that can at some point in the viral cycle commandeer host cells and use them to synthesis viral components from which progeny corona are assembled and eventually released
Archeal viruses
Few have been identified
Neuraminidase spikes
Functions in release of mature virions from the host cell
Three modes of entry normally used with animal viruses
Fusion of the viral envelope with the hosts cell plasma membrane Entry by endocytosis Release of viral nucleic acid into the cytoplasm of the host cell (can rupture membrane)
Synthesis stage right gene expression and protein synthesis regulation
Genes and proteins referred to early middle and late based on when they are expressed Early- taking over cell Middle- replication of viral genome and activation of expression of late Late- capsid proteins, self assembly and release
Viruses have been classified into numerous families based on
Genome structure Life cycle Morphology Genetic relatedness
Listeria monocytogenes
Gram positive rod found in soil and many environmental sites. Cold salt and acid tolerant. Targets young old children pregnant and immunocompromised with high death rate Hot dogs
HIV host binding
HIV binds to CD4 and CCR5 cytokines bindings sites, signaling molecules used by the immune system
Relatively few RNA viruses
Have dsRNA genomes, ssRNA more common
Describes types of capsid symmetry
Helical Icosahedral Complex Binal
Capsomers of 6 protomers
Hexamers Generally form edges and triangular face
Compare the structure of an icosahedral capsid and a helica capsid.
Icosahedral most efficient way to enclose space like a bobble head Helica like a straw tube
Viruses extracellularly
Inactive because they possess few if any enzymes and cannot reproduce outside of living cells
Viruses can exist
Intercellularly or extracellularly
Lysing release especially common for viruses and some nonenveloped animal viruses
Involves activity of viral proteins
nonenveloped or naked viruses
Lack an envelope
Define the term acellular
Not considered living so not meet living criteria microbes
Identify the parts of a virion and describe their function
Nucleocapsid - nucleic acid and capsid Nucleic acid- genome Capsid- protein coat, protective and other Protomers- make up capsid Envelope- external lipid layer Spikes/peplomers- proteins that function to attach or ID
What is difference between nucleocapsid and capsid
Nucleocapsid is the combination of the genome and the capsid The outer most protective layer of virus is called capsid. A capsid is a protein coat; it encloses the nucleic acid or genome of the virus. The individual components of capsid are called capsomeres. Capsid offers protection to the underlying nucleic acids from nucleases in the environment.
The length of helical capsid is determined by
Nucleus acid because does not extend beyond end of viral genome
bacteriophages (phages)
Numerous viruses infect bacteria
Entry: fusion of the viral envelope with the hosts plasma membrane
Often involves viral envelope glycoproteins that interact with proteins in the plasma membrane of host Interaction sets in motion events allowing nucleocapsid to enter
Viral replication complexes
Rearranged host membranes to enclose machine ties needed for genome replication transcription and protein synthesis
Entry into the host
Second step in viral multiplication Viruses genome or the entire nucleocapsid enters cytoplasm Many bacteriophages only nucleic acid enters, leave capsid out attached to cell
Virion release
Several release mechanisms have been identified Lysing the host cell Release by budding
Diameters of helica capsid is function of
Size shape and interactions of protomers
Synthesis in cytoplasm
Some plant and animal viruses To protect from host defenses reorganize the hosts membranes to enclose needed machinery
Capsids of Complex Symmetry
Some viruses do not fit into the category of having helical or icosahedral capsids poxviruses - largest animal virus large bacteriophages - binal symmetry head resembles icosahedral, tail is helical
Capsid
Surrounds viral nucleus acid Protects viral genome AIDS in transfer between host cells
How are viruses similar to cellular organisms? In what fundamental way do they differ?
Virus are similar because have nucleic acid for genome, use DNA. They cannot reproduce or metabolize independently.
Protomers
capsid proteins
Virion
complete virus particle
Bacterial viruses nucleic acid types
dsDNA
Cellular genomes are always
dsDNA
Viruses employ all 4 possible nucleocapsid acid types
dsDNA ssDNA dsRNA ssRNA
Most DNA viruses use .... as their genetic material
dsDNA (some may use ssDNA) both can be linear or circular
Viruses can infect
every type of cell
Segmented genomes
genomes that consist of more than one piece In some rna viruses Each segment codes for one protein Usually all enclosed in the same capsid
Three types of capsid symmetry
helical, icosahedral, complex
spikes (peplomers)
protein used for attachment, escape. Extend from envelope can also be used for identification
Helical capsids
shaped like hollow tubes with protein walls
Plant viruses nucleic acid types
ssRNA
Virology
study of viruses
Animal virus envelopes
usually arise from host cell plasma or nuclear membranes Envelope lipids and carbohydrates are acquired from host
Pleomorphic
variable shape
Viroplasms
viral factories, discrete sites within the cytoplasm of host cells where viruses replicate concentrated vira genomes mRNA and proteins
Enveloped viruses
viruses with virions having an envelope
Viruses
A unique group of infectious agents who's distinctiveness resides in their simple acellular organization and pattern of multiplication. Despite simplicity cause major diseases
Two functions spikes might serve in the viral life cycle and the proteins that the influenza virus uses in these processes
1. Attach to surface of host cells (hemagluttinin) 2. Release virus from cell once mature (neuraminidase)
Icosahedral assemblages
Capsomers
Envelope
A lipid layer external to the nucleocapsid
RNA viruses synthesis
-use their genome directly as m-RNA that is transcribed by host ribosomes into viral protein -use their genome as a template for generating more viral cores Have to bring their stuff cause if host not have it
Nucleocapsid
A nucleus acid (RNA/DNA) and a protein coat called capsid
Virions range in size from
10-400 NN in diameter Smallest size of ribosomes, largest is mimivirus
State the size range of virions
10-400 nm in diameter
Which virus would have a longer helical capsid a virus with a 7,200 base pair DNA genome or one with 11,000 base ssRNA genome
11,000
Virus disease examples
2003 SARS 2009 H1N1 influenza 2013 avian flu 2013 Middle East respiratory syndrome coronavirus (MERS-CoV)
Hemagglutinin spikes
Bind virions to red blood cells and cause cells to clump together (hemagluttinattion)
The RNA genomes of some RNA viruses resemble the messenger RNA of their eukaryotic hosts what advantages would an RNA virus gain by having this type of genome
Can have their DNA translated using host machinery Can help start the infection proliferation quicker
envelope proteins
Coded for by viral genes and may project from envelope as spikes
The various morphological types of virions primarily result from
Combination of particular type of capsid symmetry with the presence or absence of an envelope
2011 L.monocytogenes outbreak
Contaminated cantaloupe Killed 20
Synthesis stage
Cycle differs dramatically among viruses because genome dictates
Most important advantage of virus design strategy is
Maximum efficiency
Although viruses lack true metabolism and cannot reproduce independent of livi NB cells their virions...
May carry one or more enzymes essential to the completion of their life cycles
Icosahedral capsids
Most efficient way to enclose a space Constructed from ring or knob shaped assemblages of 5 or 6 protomers
Eukaryotic viruses
Most known viruses infect eukaryotic cells Plants animals protists fungi
Because cell surface proteins are vital for cellular function
Mutations that change them significantly are not tolerated, ensures virus can infect host
Entry: Endocytosis
Nonenveloped and some enveloped Endocytic pathways Endocytic vesicles contains the biriom and fuses with endoscope can aid in uncoating
Delbuck and Ellis 1939
One step growth experiment How pyrogeny viruses made Used phage T4 And E. coli Diluted after reduction Plague assay Latent period occurs after phage edition
Capsomers of 5 protomers
Pentamers Usually at the vertices of the icosahedron
No receptors have been identified for
Plant viruses (host must be damaged for entry)
ssRNA genome viruses
Polio Tobacco mosaic SARS Rabies Mumps Measles Influenza Human immunodeficiency Brome mosaic
Size of helical capsid influenced by
Protomers and viral genome
Assembly (viral replication)
Quite complex Complete nucleocapsid construction
Why do some envelope viruses have pleomorphic virions
The envelope is not always structured or anchored to the nucleocapsid
Distribution at the tissue level plays a crucial role in determining
The tropism of the virus and outcome of infection
Eukaryotic cell membranes have micro domains often called lipid rafts
Thought to be involved in virion entrance and assembly
Viruses as model organisms
Understanding DNA replication RNA synthesis Protein synthesis
Some viruses have enzymes within their capsids
Usually involved in nucleus acid replication
The size of viral genomes
Varies greatly
dsDNA synthesis
Very similar to topics flow of information Stored in dna Replicated by DNA polymerase Recoded as mRNA Coded during protein synthesis Can depend solely on host cells bio synthetic machinery to replicate genomes and synthesis proteins
Virus factories
Viral replication complexes and viroplasms
Distinguish envelope from no envelope virus
Virion has an envelope or not
Define the terms virology, bacteriophages, and phages
Virology- study of viruses Bacteriophages- viruses that infect bacteria Phages- another word for bacteriophages
Need light microscope to view
Viruses
Compare and contrast in general terms viruses, viroids, satellites and prions
Viruses- smallest Viroids/satellites - infectious RNA Prions - infectious proteins
Why viruses are good
Vital members of aquatic ecosystems Interact with cellular microbes and contribute to the movement of organic matter from particulate to dissolved form Important model organisms Used to treat bacterial infections
The nucleocapsid of eukaryotic viruses enters the cytoplasm
With the genome still enclosed, once inside some shed capsid proteins (uncoating)
