Test Questions on viruses – Microbiology – Flashcards
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Unlock answers| Early development of Virology |
Many Epidemics of viral diseases occured before anyone understood the nature of their causative agents
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Early Attempts to prevent viral diseases
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Lady Wortley Montagu ( 1700s)- Inoculated children with material from small pox lesion, got idea from turkish women
Edward Jenner ( 1798) - tried to prevent small pox by exposure to cow pox |
Discovery of viruses 1800s
* Charles Chamberland
* Dimitri Ivanowski |
* invented a porcelein bacterial filter used later in the discovery of viruses
* Demonstrated that causative agent of tobacco mosaic diease passed through bacterial filters, thought agent was toxin
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Discovery of Viruses
* Martinus Beijerinick |
| showed that the causative agent of tabacco mosaic disease was still infectious after filtration referred to agent as filterable virus |
| Loeffler and Frosch |
| showed that hoof and mouth disease in catte was caused by a virus |
| Walter Reed |
| Showed tht yellow fever in humans was caused by a filterable virus transmitted by a mesquito |
| Ellerman and Bang |
| Showed that Leukemia in chiickens was caused by the virus |
| Peyton Rous |
| Showed that muscle tumor in chicken was caused by a virus |
| Fredrick Twort |
| first to isolate viruses that infect bacteria ( bacteriophages) |
Felix d'Helle did what 3 things |
Firmly estabished the existance of bacteriophages Devised method for enumerating them demonstrated that bactreriophages only reproduce in live bacteria |
| Are viruses living or non-living entities |
| non-living entities |
| Are viruses considered living organisms? |
| no |
| Can virused infect organisms of all life forms? |
| yes |
| ;Viruses are Obligate intercellular parasites |
| True |
| Are viruses able to reproduce outside a living cell? |
| no |
| Viruses |
Simple organism DNA or RNA not both unable to reproduce outside of living cell obligate intercellular parasite |
| Cellular organisms |
Complex organism Both DNA and RNA carry out cell division some are obligate intracellular parasites |
| True of False some cellular organisms are obligate intracellular parasites |
| true |
| Virion |
| complete virus particle |
| what does a virion consist of |
| nucleic acid surrounded by a protein coat |
| The protein of a virus is termed what |
a capsid ; |
| what is the capsid (protein coat) of a virus composed of |
| capsomeres |
| What is the main purpose of the protein coat (capsid) of a virus |
| To protect genome and aids in transfer between host cells |
| True or false sometimes enzymes are included within the capsid |
| true |
| Many capsids have additional layers? |
| true |
| Virions ( the complete virus particle) can be Naked or enveloped true or false |
| True |
| Naked Virions |
| are without an envelope |
| Virions with an envelope are |
| surrounded by a lipid mebrane |
| Viral envelopes |
| membrane structures aurrounding some viruses |
| Lipid and carbohydrates in the virus envelope are usually derived from |
| host membranes |
| Peplomers |
| (spikes) are proteins in the envelope and are virus specific |
| Do viruses have different shapes? |
| yes |
| Helical capsids |
| shaped like hollow tube with protein walls |
| Icosahedral Capsid |
| Regular polyhedron with 20 equilateral triangular faces and 12 vertices |
| What is a complex virus |
| viruses with capsids of complex symmetry |
| A viral genome contains how many types of nucleic acid |
1 either DNA of RNA never both |
| A viral genome can be single stranded or double stranded and can be linear or circular? |
| true |
| Viruses can;only;multiply inside metabolizing cell? |
| true, use host machinary to support reproduction |
| Every virus contains information to- |
make viral proteins assure replication move in and out of host cell |
| What two phases do viruses live in |
extracellular phase metaboliclly inert intracellular phase metabolically active |
| Bacteriophage classification;are based on two major criteria |
phage morphology nucleic acid properties |
| When the virus enters the host cell the effect on the cell depends on the |
| infecting phage |
| the infecting bacteriophage can infect the host cell in two ways |
| Some phages multiply in host cell, producing numerous progeny but other phages integrate into host genome |
| The lytic cycle of viral reproduction |
| Viral life cycle that cumulates with host cell bursting, releasing viral particles |
| The lytic cycle involving virulous agents |
| lyse their host cells during the reproductive cycle |
| 5 stages of viral reproduction |
- absorbtion/ attachment -penetration - synthesis -assembly -release |
penetration and uncoating during penetration |
entrance of the virus or its nucleic acid into the host cell viral genome is released |
| synthesis |
| production of viral nucleic acid and protein |
| assembly |
| making the viral particles |
| release |
| viral particles are leaving the cell |
The lytic cyles: absorbtion / attachment |
The phage collide by chance with the bacteria the base plate with its tail spikes settles in on the surface of the bacterium |
| Receptor sites during absorbtion/attachment of the lytic cycle |
specific surface structure on host of which viruses attach they are specific for each virus some can be lipopolysacharides, techoic acids..etc |
| During the lytic cycle : attachment and penetration |
| The bacterial viruses inject the nucleic acid into the host through the cell |
Synthesis of the lytic cycle Sequential steps |
duplication of viral components is a sequential process ;1. Virus will inhibit activity of the host DNA -Viruses produce enzymes to destroy host DNA 2. Viral DNA takes over anf begins transcribing mRNA -early mRNA synthesis - Late mRNA synthesis |
| Early mRNA synthesis |
| early viral proteins are associated with the replication of viral nucleic acid |
| Late mRNA synthesis |
| encode capsid proteins and other proteins needed for phage assembly |
| Assembly |
| The protein structures of the phage such as heads, tails,tail spikes and tail fibers are synthesized independantly of one another, the replicated viral components are assembled into an intact, mature virus particle |
| scaffolding protein |
| viral encoded proteins aid in construction of procapsid |
| Realease of Phage particles during the lytic cycle |
| T4 lysis of host is brought about by several proteins |
| two examples of the many proteins that are involved in T4 lysis of the host cell |
endolysin- attack peptidoglycan holin- produces lesions in the cell membrane |
| Other things that help T4 lysis of host cell |
| production of enzymes that disrupt cell wall construction, host cell bursts and releases viruses to the outside enviroment |
| How many pathways are there to the lytic cycle |
| two |
| Viral reproduction: lysogeny |
| a- non lytic relationship between a virus and its host, usually involves viral genome into host DNA, contains a prophage |
| Twp types of viral reproduction |
lytic cycle- virus replicates in the cell and the cell eventually burts lysogeny- the virus integrates viral genome into host DNA |
| prophage |
| integrated phage genome |
| Temperate phage |
| phage able to resist lysogeny |
lysogens ; |
| Lysogenic bacteria, infected bacteria host |
| An example of lysogeny |
| Lambda Virus |
| Lambda Virus |
lysogeny begins like the lytic cycle attachment/absorbtion penetration... double stranded DNA phage ;its genome circularizes upon entry into the host ; |
| How is Lysogeny and the lytic cycle controlled |
incorporation depends on the production and competition of two regular proteins: Lambda repressor Cro protein |
| lambda repressor |
| blocks transcription of the lytic genes, including cro genes |
| cro protein |
involved in regulating lytic cycle genes blocks the synthesis of the lambda repressor |
| How do we know which repressor becomes functional first |
| it depends on the various circumstannces and is not completely understood |
| during lysogeny and lytic control if the lambda repressor wins the competition |
then the viral nucleic acid will incorporate into the host chromosome, and integrase will catalyse integration the viral DNA is replicated only when the host cell replicates, this allows for the population of the bacterial cells to carry viruses |
| what happens during the lytic/lysogeny cycle when the cro protein wins |
| the lytic cycle occurs |
| During lysogeny/ lytic control once incorporated the repressor protein continues to be produced at low levels this process is reversable |
| true |
| induction |
| phage production is initiated |
| What is induction triggered by |
| damage to chromosomal DNA ( SOS repair causes drop in repressor protein), the excising of the viral genome initiates the lytic cycle |
| the excising of the viral genome initiated the lytic cycle |
| true |
| during lysogenic conversion prophage can cause change in the |
| host phenotype |
| Lysogenic conversion the phage DNA is not completly suppressed because |
| the gene coding for the new trait are expressed in the bacterium |
| filamentous phages |
| single stranded DNA viruses that appear as long thin filaments, some of these phages do not undergo lysogeny pr follow the lytic cycle, the infected bacteria continue to grow and reproduce, the viral genome and proteins are also produced |
| filamentous phages |
the virion is extruded from the cell the capsid proteins are stored in the bacterial membrane as the DNA is extruded, the virion is assembled this occurs continuously and the infected cells are the carriers |
Transduction ; |
bacteria DNA that is transferred from donor to recipitant via bacteriophage two types generalized and specialized |
| generalized tranduction |
| any gene of donor can be transferred |
| specialized transduction |
| only specific genes can be transferred |
| generalized transduction |
any part of the bacterial genome can be transferred occurs during the lytic cycle of virus replication during viral assembly, fragments of host DNA are mistankenly packed into phage head forming generalized transducing particles |
| embly |
| specialized transduction is also called |
| restrictiong transduction |
| specializeds transduction is carrier out only by |
| temperate phages that have established lysogeny, only specific portion of bacterial genome is transferred |
| when; does specialized transduction occur |
| when prophage is incorrectly excised |
| the bacterium containnig prophage during specialized transduction |
induction occurs and begins viral replication the excised genome contains a portion of the bacterial chromosome |
| what contains the altered DNA in specialized transduction |
| the assembled phage particles |
| During specialized transduction virus particles are released and infect new cells, the piece of bacterial chromosome becomes incorporated into the new host genome |
| true |
| host range |
| the number of different bacteria that a phage can infect, usually limited to a single bacteria or a single strand for a single phage |
| two most important factors that limit host range |
phage must be able to attach to host receptors restriction-modification system of the host cell must be overcome |
| host ranges for phages receptors on bacterial surface |
| vary in chemical structure and location usually on bacteria cell wall |
host ranges for phages receptor sites can be altered by two mechanisms ; |
mutation lysogenized bacteria can alter cell surface, which results in alteration of receptor site |
| host ranges for phages: restriction modification system what does the restriction part do |
| bacteria have two genes coding for enzymes of restriction modification system, restriction enzymes that codes for endonuclease cuts small segments of DNA |
| what does the modification part of the test do? |
| modification enzyme attached methyl group to DNA sequence recognizing by restriction enzyme , methylated bases are not recognized by restriction enzymed, this protects cells own DNA |
