virus flashcards
What is a virion?
A complete viral particle, including a nucleic acid and a capsid, outside of a cell.
How do RNA animal viruses synthesize within their host cells?
RNA viruses are replicated and assembled in the cytoplasm. Some have positive sense strands and some have negative sense strands.
What is a retrovirus?
It referes to a group of RNA viruses that insert a DNA copy of their genome into the host cell in order to replicate, e.g., HIV.
What are the living characteristics of viruses?
* Nucleic acids
* Reproduction
* Respond to stimuli
* Evolve
Describe endocytosis in reference to animal viruses’ entrance into host cells
* Virus recognizes and attaches to the host membrane with spikes.
* This connection stimulates host to endocytize the virus.
* Once inside, uncoating occurs releasing nucleic acid into cytoplasm.
What happens during the ‘lysis’ stage duirng bacteriophage replication.
Lysozyme is used to lyse the host bacterial cells, this allows viruses to escape.
What are some methods for handeling piron contamination?
* Normal cooking or sterilization procedures do not deactivate prions, though incineration or autoclaving under harsh conditions can work.
* Enzymes have now been employed to help disinfect prion contaminated medicalm equipment.
What happens during ‘synthesis’ phase of bacteriophage replication?
* The bacterial cell replicate viral DNA.
* Protein synthesis is takes place making capsids, proteins, and nuclease.
* Nuclease destroys bacterial DNA so host has only viral DNA.
What are the steps in the Lysogenic replication of bacteriophages?
* Attachment
* Entry
* Lysogeny
* Induction
* Synthesis
* Assembly
* Release by lysis
What happens during the ‘Induction’ phase of the lysogenic cycle for bacteriophages?
Due to environmental stimulus the prophage comes out of bacterial DNA, takes over the cell, and the lytic phase of the cycle begins.
What is a Nucleocapsid?
the capsid of a virus with the enclosed nucleic acid
What is host range in reference to viruses?
Because viruses need an exact fit between virus spikes and cell receptors, host range refers to the number/type of cells a virus can infect
What are bacteriophages?
Bacteriophages are viruses that attack bacteria.
When talking about viruses, what is latency
Latency refers to stages of dormancy in which viruses have oscillating patterns of activity and inactivity. This is found only in some viruses such as chicken pox or herpes
What is a virus?
A minuscule, acellular, infectious agent usually having one or several pieces of nucleic acid—either DNA or RNA
What are capsomeres?
The proteinaceous subunits that make up the capsid of a virus
What are prions?
An infectious agent that lacks instructional nucleic acid. Prions cause normal proteins to misshape into Prion PrP proteins.
What are the 3 different types of media used for culturing viruses?
- * Mature organisms – viral plaques on a lawn of bacterial growthgrowth
- * Embryonated eggs – chicken eggs are large, sterile self sufficient cells with multiple sites for growth
- * Cell cultures – cells isolated from an organism and grown on media or in broth. Continuous cultures come from tumor cells and can divide continually.
What happens during the “attachment” phase during bacteriophage replication?
The virus engages a host cell by chance collision; Viruses do not move on their own.
What are proto-oncogenes?
* They are genes that play a role in cell division
*Several genetic changes must occur before these genes are no longer repressed or for cancer to develop
* Viruses cause 20-25% of human cancers by carrying copies of oncogenes, by promoting those already present, or possibly interfering with normal repression.
What are the 3 modes of action for antiviral drugs?
- * Halting penetration of virus into host cell Blocking transcription and/or translation
- * Preventing assembly, or maturation of viral pieces
- * Antiviral drugs protect uninfected cells, but don‟t do much for extracellular viruses or latent viruses
What are the four types of nucleic acids found In viruses and describe each of them:
- Double stranded DNA - Acts as normal DNA would, transcription and translation are the same.
- Single stranded DNA - only half of the normal DNA, A complementary strand is created and then the strand will acts as a normal double stranded dna.
- single stranded RNA - Can directly act as mRNA, a - single stranded RNA Stand is created as a template for more +ssRNA.
- -ssRNA - must have a Compliment +ssRNA strand created for both protein synthesis and as a template to create more -ssRNA
How do DNA animal viruses synthesize within their host cell?
DNA viruses enter the host cell nucleus and are replicated and assembled there
In phage typing what is plaque?
The clear region within the bacterial lawn where growth is inhibited by bacteriophages
What are the 3 parts that make up a virus?
* Nucleic acid core – one or many strands of DNA or RNA but not both
* Capsid – protective outer shell made of protein subunits called capsomeres
* Envelope – optional, not all viruses have this. Usually a modified piece of the hosts cell membrane.
What are pirons composed of?
A protein called PrP
What are some benefits to bacteriophage treatment?
* Highly specific, attacking only targeted bacterial cells
* Cheap
* Effective in small doses
* Rarely cause side effects
* Replicate significantly faster than bacteria 100s per burst vs. doubling by binary fission
* Cleaned out of body (by reticuloendothelial system) once bacteria are gone and can no longer replicate
In membrane fusion what does uncoating refer to?
In animal viruses, the removal of aviral capsid within a host cell.
What is a Prophage?
It is an inactive bacteriophage.
Viral nucleic acids contain genes for at least 4 things, what are they?
* Genes for regulating the actions of the host
* Genes for synthesizing the viral genetic material
* Genes for synthesizing the viral capsid and proteins
* Genes for assembling and packaging the mature virus.
What are some of the actions of the viral envelope?
* Protection - The outer layer protects the viron from enymes and chemicals ouside of the host cell.
* Penetration - The outer layers of the envelope bind to the host and assist in insertion of the viral nucleic acid into the host cell.
* Activiation - Portions of the caspids and envelopes stimulate the immune system to produce antibodies against the virus
Describe membrance fusion in reference to animal viruses’ entrance into host cells
* Virus recognizes and attaches to the host membrane with spikes.
* Viral envelope and host cell membrane fuse.
* Capsid is released into cytoplasm leaving behind the envelope and glycoproteins.
* Uncoating occurs releasing nucleic acid into cytoplasm
In what ways do animal viruses leave their host cell?
Non enveloped and complex viruses will usually lyse or rupture the host cell, they may also leave by a modified type of exocytosis (but do not acquire an envelope)
* Enveloped viruses are released by a process called budding, during which they acquire their envelope.
How could lysogeny affect human disease?
Lysogency can affect human disease by making an unharmful bacteria more harmful through lysogenic conversion.
What are the non-living characteristics of viruses?
* DNA or RNA, not both
* Obligate intracellular parasite
* No growth or metabolism
* No cell structure
What are the steps in the Lytic replication of bacteriophages?
* Attachment
* Entry
* Synthesis
* Assembly
* Release by lysis
What is budding, in reference to viruses?
* Enveloped viruses are released by a process called budding, during which they acquire their envelope.
* Budding begins with the nucleocapsid binding to a membrane.
What is an envelope in reference to viruses?
An optional modified piece of the hosts cell
What happens during the “assembly” phase of bacteriophage replication?
During this phase the viral parts come together, chemical reactions bring and glue pieces together.
What are some differences between the lytic cycle and the lysogenic cylce in bactriophage development?
* The lytic cycle kills bacteria relatively quickly whereas the lysogenic cycle will not immediately kill the host
* In the lysogenic cycle viral DNA becomes inserted into the DNA of the bacterium, becoming a physical part of the bacterial chromosome.
What is the viral envelope made of?
* The viral envelope is made of the host‟s cell membrane
What is exocytosis?
A process by which the contents of a cell vacuole are released to the exterior through fusion of the vacuole membrane with the cell membrane.
One method animal viruses leave thier host cell is through a process called budding, describe this process.
* Budding begins with the nucleocapsid binding to a membrane (nuclear, ER or cytoplasmic)
* The membrane forms a pouch and then that pouch pinches off the host cell and forms the envelope.
* This is a gradual process of shedding viruses.
What is a capsid?
Protective outer shell made of protein subunits called capsomeres
What are the 3 methods that animals viruses enter their host cells:
* Direct penetration
* Membrane fusion
* Endocytosis
Describe direct penetration in reference to animal virus’ entrance into host cells
* Virus recognizes and attaches to the host membrane with spikes.
* Virus capsid “sinks” into the membrane creating a pore.
* Nucleic acid enters cell alone.
What happens during the ‘entry’ phase during bacteriophage replication?
A chemical interaction caused by the contraction of the bacteriophage’s tail takes place in which the bacteriophage injects DNA into bacterial cell, leaving behind a ghost phage.
List and describe the 3 basic shapes of viruses
* Helical - Viruses bonded to form a series of hollow discs, then bound together to form a hallow tube.
* Polyhedral - Viruses that are 3 dimensional, 20 sided, with 12 evenly spaced corners.
* Complex - The virus shape has a more intricate or varied structure.
What tissue do piron’s infect and how do they do so?
Piron’s infect cellular PrP and •Prion PrP enzymatically induces cellular PrP to “shape flip” to become prion PrP.
