Viruses And Other Infectious Agents Flashcards
Describe the initial experiments used to discover the existence of viruses
Filtration experiments:
- extract and filter infectious liquid
- inject filtered liquid into healthy animal
- filter liquid cause disease
- infectious agent is smaller than bacteria therefore in the liquid
Explain why Microscope techniques available in the late 1800s where not capable of visualizing viruses and what form of microscopy was able to confirm the existence of viral particles
Viruses are so small they’re unable to be seen with the light microscope. In the late 1930s electron microscope’s were used to visualize the tobacco mosaic virus 160,000 times magnification
Define the concept of host range as it applies to viruses and based on the principle of virus structure and function explain why viruses are generally able to infect a specific type of cell
Host range; viruses tend to infect specific cell types
Narrow groups of cell types to infect evolutionarily types of similarities narrow key truly unique to the cell type that infects
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Draw the structure of the virion and describe the major common and components found in a virion And distinguish the structure is not an animal and not animal viruses
Genome type and composition: DNA/our name can be single or double stranded sense or anti sense
Capsid (and capsomere) Protein coat always present surrounding nucleic acid
capsomere Visual proteins up unit that forms a protective shell known as capsid
Spikes (and composition) : Glycoprotein complexes use that to host cell that come off the capsid
Envelope: Outer lipid layer
( only an animal virus )
*draw
Generally describe how viral taxonomy it works and understand the general limitations of the size of viral genome
Based on the nature Of the viral genome smallest set of proteins that a virus needs to carry out its life cycle
DNA viruses: ds dna, ss dna,
RNA viruses: ds rna,+ss rna, -ss rna
Retro viruses: HIV 9 genomes total
Ss rna retro, ds dna retro
Any group of RNA viruses in which insert a dna copy of the genome into the host in order to replicate
Know the common viral morphologies
Helical viruses : tobacco mosaic virus, capsid with rna
Polyhedral viruses : made of adenovirus
Enveloped viruses (only animal) May be helical or polyhedral
Complex viruses: (bacteriophage)
Head contains dna, collar, sheath, base plate tail fibers
Infect only bacteria, can kill bacterial cells
**know how to draw and label **
Describe the general function of spikes on viruses, and in particular the function of the spikes surrounding the influenza virus and how spike composition defines subtype
Spike composition determines the subtype
Subtype h1n1 h2n1 etc**
Hemagglutinin: Causes red blood cells to clump allows virus to enter cell
Neuraminidase: Cleaves sialic acid at cell surface, allows virus to leave cell.
Spike proteins are specifically made to attach to certain cell receptors that may only be present in specific cells
Explain the methods by which scientist grow viruses for research or vaccine production
Phage growth on a bacterial lawn and plaque formation: Used to kill the bacteria with the virus attacks bacterial infection with bacterial phage specific bacteria that formation indicates viral infection (holes in plaque)
Cell culture and that cytopathic affect on virally infected eukaryotic cells: Host cell grown in lab infected with the virus cutopathic affect disease change due to viral infection of cell
Uses of embryonated egg: Used for many viruses vaccine today flu virus
Virus production in living organisms: ?
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Describe the major differences and similarities between the lytic and lysogenic cycles
Lytic cycle: Virus makes everything needed to assemble new virus kills infected cell upon exit. Model virus- bacteriophage T4
Lysogenic cycle : Virus integrates into host chromosome waiting for the right moment to emerge. model- bacteriophage lambda
For the lytic cycle Explain the steps by which a bacterial phage carries out it’s reproductive cycle and the affect on the bacterial host resulting from page infection
Attachment: to host cell
penetration: of host cell by viral DNA
- virus rudely injects it’s DNA into cell and destroys host cell DNA
biosynthesis: of viral components
- uses host cell’s ribosomes and resources to make phage components using information in phage
maturation: of viral components into mature virions
release: of freshly made viral particles by cell lysis (rupture)
For the lysogenic cycle Describe the steps by which a phage integrates it’s genetic information into the bacterial chromosome to form prophage And the effect this can have on the host bacterium
Attachment: to host cell
penetration: injects DNA into host cell
integration and prophase formation: viral DNA integrates into host chromosomes
Prophage viral genome integrated into host genome changes infectious properties of bacterium
reproduction of lysogenic bacterium: reproduces normal binary fission
Phage conversion: replicated during division
Prophage exit from lysogenic cycle
Escapes occasionally and renters lytic cycle
**examples: diphtheria, botulism, pathogenic E. coli , toxic shock syndrome
Describe the major differences between the reproductive cycle in an animal and virus phages
Entry of virion into cell via receptor-
mediated endocytosis: entire virion is brought intact into the cell
or
fusion: envelope fuses with plasma membrane, capsid enters
Uncoating: capsid disassembles releasing viral genetic information
Release of newly formed viruses by budding
Forming the envelope around the capsid
List some common DNA viruses and explain the shared reproductive characteristics
DNA viruses that infect eukaryotic cells
Canine parvovirus
Herpesvirus (cold sores)
Papovavirus (hpv)
Pox viruses (smallpox): bring own enzyme to make mRNA
Key features: dna is transcribed to mRNA in the nucleus
Or
DNA is transcribed to mRNA in the cytoplasm using a viral enzyme
Transcribed mRNA then used to make virions
List common RNA viruses and describe how viral components are produced within an infected cell
Key feature: virus contains its own RNA- dependent rna polymerase which make mRNA in the cytoplasm
Examples:
Poliovirus
Lyssavirus (rabies)
Filovirus (Ebola)
List some common retroviruses explain how retroviruses can integrate their genetic information into the host cells genome
Describe how integration could lead to
Latent infections
Can remain hidden in genome forever
cancer
Can cause if integrated into bad spot in host cells genome
provirus formation: viral ds dna integrates into host genome as a provirus
Contain reverse transcriptase: create ds dna from viral rna
Examples: lentiviruses (hiv) Delta retroviruses (human t lymphotrophic virus- causes cancer )