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Chapter 8: Viruses and Their Replication
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- 1virus- obligate intracellular parasites
- infectious nucleic acid surrounded by protein, not considered living entities
- relies on host cell for energy, metabolic intermediates, protein synthesis & replication - 2VIRAL COMPONENTS virion- extracellular form, outside of cell
- protects viral genome & allows virus to travel from one cell to another
- includes capsid (protein shell) & genome
- has proteins on surface that aid attachment to cells - 3VIRAL COMPONENTS Most bacterial viruses are naked, with ____ further layers , whereas many animal viruses have an outer layer called the _____- no
- envelope - 4VIRAL COMPONENTS envelope- outer layer consisting of phospholipid bilayer (taken from the host cell membrane) and viral proteins
- 5VIRAL COMPONENTS nucleocapsid- In enveloped viruses
- the inner structure of nucleic acid plus capsid protein - 6lytic infection- virus redirects the host cell’s metabolism from growth to support virus replication and the assembly of new virions
- Eventually, new virions are released, and the process can repeat itself - 7lysogenic infection- host cell is not destroyed
- host cell is genetically altered
- the viral genome becomes part of the host genome - 8VIRAL GENOMES- DNA or RNA
- some viruses use DNA & RNA at different stages in their replication cycle
- can be single-stranded (ss) or double-stranded (ds)
- circular or linear - 9VIRAL GENOMES single stranded viral genomes may be _____ or _____ sense in terms of their base sequence- plus
- minus - 10VIRAL GENOMES plus sensehave the exact same base sequence as that of the viral mRNA that will be translated
- 11VIRAL GENOMES minus sensecomplementary in base sequence to viral mRNA
- 12VIRAL GENOMES Viral genomes are typically _____ than those of cellssmaller
- 13VIRAL GENOMES Most viral genomes encode from ___ to ___ genes. ___ viruses typically have the smallest genomes. only ___ viruses have genomes encoding more than 40 genes- 2
- 350
- RNA
- DNA - 14bacteriophagesBacterial viruses
- 15Most viruses are smaller than prokaryotic cells, ranging in size from _____ to _____ μm- 0.02
- 0.3 - 16VIRION STRUCTURE capsid- shell of a virus
- made of individual protein molecules (capsomeres) arranged in a precise and highly repetitive pattern around the nucleic acid - 17VIRION STRUCTURE small size of most viral genomes restricts the number of viral proteins that can be encoded. thus, a few viruses have only _____ _____ in their capsidone protein
- 18VIRION STRUCTURE Virions are highly symmetric, w/2 types: ___ shaped with _____ symmetry and _____ shape with _____ symmetry- rod
- helical
- spherical
- icosahedral - 19VIRION STRUCTURE helical symmetry length is determined by ...; its width is determined by ...- the length of the nucleic acid
- the size and packaging of the capsomeres - 20VIRION STRUCTURE helical symmetry visual
- 21VIRION STRUCTURE helical symmetry
- 22VIRION STRUCTURE icosahedral symmetry- has 20 triangular faces and 12 vertices
- roughly spherical in shape
- most efficient, requires the smallest number of capsomeres to build the shell - 23VIRION STRUCTURE icosahedral symmetry visual
- 24VIRION STRUCTURE for icosahedral symmetry the simplest arrangement of capsomeres is ___ per triangular face, for a total of 60 capsomeres per virion. multiples of _____, _____ and ____ are more common- 3
- 180
- 240
- 360 - 25VIRION STRUCTURE The most structurally complex of all viruses are the _____ bacteriophageshead-plus-tail
- 26VIRION STRUCTURE envelope- lipoprotein membrane surrounding the nucleocapsid
- contains primarily host cytoplasmic membrane, but some viral surface proteins - 27VIRION STRUCTURE envelope uses proteins on the virion’s envelope to ____ to animal cells. it fuses with the _____ ______. it also faciliatates ...- attach
- host membrane
- exit from cells - 28VIRION STRUCTURE plant and bacterial cells are surrounded by a _____ ____ outside the cytoplasmic membrane, and thus _____ examples of enveloped viruses are known in these organisms- cell wall
- few - 29VIRION STRUCTURE As they pass out of the host cell, they are draped in _____ _____ materialcytoplasmic membrane
- 30VIRION STRUCTURE The virus-specific envelope proteins are critical for two things:- attachment of the virion to the host cell during infection
- release of the virion from the host cell after replication - 31VIRION STRUCTURE some bacteriophages contain an enzyme that resembles _____ used to make a small _____ in the bacterium’s peptidoglycan layer to allow _____ _____ from the virion to get into the host cytoplasm- lysozyme
- hole
- nucleic acid - 32VIRION STRUCTURE Another enzyme is produced in the later stages of infection to _____ the host cell and release new virionslyse
- 33VIRION STRUCTURE neuraminidases- envelope proteins that destroy glycoproteins and glycolipids of animal cell connective tissue, thus liberating the virions
- 34VIRION STRUCTURE RNA replicases- RNA virion enzyme
- RNA-dependent RNA polymerases - 35VIRION STRUCTURE RNA replicases are needed because ...- DNA polymerase can't make RNA
- cells lack enzymes that can make RNA from an RNA template - 36VIRION STRUCTURE Retrovirusesunusual RNA animal viruses that replicate via DNA intermediates
- 37VIRION STRUCTURE reverse transcriptaseenzyme to reverse-transcribe their RNA genomes into DNA, which is then integrated into the host genome and replicated along with it
- 38VIRION STRUCTURE In cells of Bacteria and Archaea, only the _____ _____ enters the host cell. By contrast, in plant and animal cells, the _____ _____ is taken up- nucleic acid
- entire virion - 39VIRUS LIFE CYCLE permissive cell- A cell that supports the complete replication cycle of a virus
- 40VIRUS LIFE CYCLE 5 steps of viral replication cycle- Attachment of virion to host cell
- Penetration of nucleic acid into host cell
- Synthesis of nucleic acid & protein by host cell machinery as redirected by virus
- Assembly of capsids & packaging of viral genomes into new virions
- Release of new virions from cell - 41VIRUS LIFE CYCLE a time course of virion numbers in the culture medium shows essentially _____ increase during the replication cycle until ...- no
- cells burst and release their newly synthesized virions - 42VIRUS LIFE CYCLE eclipse phase- In the first few minutes after infection
- viral genome and proteins are replicated and translated, respectively - 43VIRUS LIFE CYCLE If the infected cell breaks open after entry, the virion no longer exists as an _____ _____ since the viral genome is no longer inside its _____.- infectious entity
- capsid - 44VIRUS LIFE CYCLE maturation phase begins as newly synthesized viral nucleic acid molecules are ... the number of infectious virions inside the host cell _____ dramatically- packaged inside their capsids
- rises - 45VIRUS LIFE CYCLE latent periodeclipse and maturation periods are combined because newly assembled virions are not yet present outside the cell
- 46VIRUS LIFE CYCLE At the end of maturation, mature virions are released, either as a result of ____ _____ or _____ or ____, depending on the virus.- cell lysis
- budding
- excretion - 47VIRUS LIFE CYCLE burst sizeThe number of virions released per cell
- 48VIRUS LIFE CYCLE duration of the virus replication cycle varies, from ___ - ___ min to ___–___ h (in most animal viruses).- 20 – 60
- 8 – 40 - 49Host cells need to be _____ in order for viruses to replicate in themgrowing
- 50Bacterial virus are cultivated in _____ _____ of bacterial hosts that are inoculated in _____ medium or spread as _____ on the surface of agar plates and then inoculated with a _____- pure cultures
- liquid
- lawns
- suspension - 51Animal viruses are cultivated in _____ _____- tissue cultures
- 52tissue cultures- cells obtained from an animal organ
- grown in sterile glass or plastic vessels containing an appropriate culture medium - 53Tissue culture media- highly complex
- has a wide assortment of nutrients: blood serum, highly nutritious substances to feed the animal cells, & antimicrobial agents to prevent bacterial contamination - 54titer- viral suspension quantified to estimate the number of infectious virions present per volume of fluid
- expressed as the number of “plaque-forming units” per milliliter - 55Plaque-based assays- standard method used to determine virus concentration in terms of infectious dose
- 56Viral plaque assaysdetermine the number of plaque forming units (pfu) in a virus sample, which is one measure of virus quantity
- 57When a virus infects host cells growing on a flat surface, a zone of cell lysis called a _____ forms and appears as a clear area in the lawn of host cells. By counting the number of plaques, one can calculate the _____ of the virus sample- plaque
- titer - 58Plating efficiency ("PE")- measure of the number of colonies originating from single cells.
- very sensitive test
- used to determine the nutritional requirements of cells, testing serum lots, measuring the effects of growth factors, and for toxicity testing - 59In any given viral preparation, the number of plaque-forming units is always _____ than actual counts of viral particles made microscopically. efficiency with which virions infect host cells is rarely _____- lower
- 100% - 60Virions that fail to infect may have ...- assembled incompletely during the maturation process
- contain defective genomes
- suffered a spontaneous mutation - 61a low plating efficiency may mean that _____ _____ conditions were not optimal or that some virions were damaged by ...- viral growth
- handling or storage conditions - 62ATTACHMENT The virion has _____ on its external surface that interact with _____ on the host cell surface. if the receptor is altered (i.e. mutation) the host may become ...- proteins
- receptors
- resistant to virus infection - 63ATTACHMENT Viral receptors are surface components of the host, such as ...proteins, carbohydrates, glycoproteins, lipids, or lipoproteins, or cell structures made from these macromolecules
- 64ATTACHMENT Appendages that project from the cell (i.e. flagella, pili) , are _____ for bacterial viruses. Small icosahedral viruses often bind to the _____ of these structures, whereas filamentous bacteriophages typically bind at the _____- receptors
- side
- tip - 65—
- 66PENETRATION Bacteriophages _____ their capsid outside the cell and only the viral genome reaches the cytoplasm- abandon
- 67PENETRATION RNA viruses require that _____ also enter the host cell along with the viral genome- enzymes
- 68—
- 69PENETRATION Bacteria and Archaea possess several weapons against viral attack:- Toxin–antitoxin modules
- CRISPR
- restriction - 70PENETRATION restrictionrestriction endonucleases can destroy
double-stranded viral DNA by cleaving foreign DNA at specific sites - 71PENETRATION host protect its own DNA from restriction by ...methylation of nucleotides at the sites where the restriction enzymes cut
- 72PENETRATION Restriction enzymes are specific for _____ _____ DNA, and thus _____ _____ DNA viruses and all _____ viruses are unaffected by restriction enzymes- double-stranded DNA
- single-stranded
- RNA - 73PENETRATION some doublestranded DNA viruses have overcome host restriction by ... so it is no longer subject to restriction enzyme attackmodifying their own DNA
- 74REPLICATION circular permutation- In a population of T4 virions, although each copy of the genome contains the same set of genes, they are arranged in a different order
- DNA appear to have been linearized by opening identical circular genomes at different locations - 75REPLICATION terminally redundantsome DNA sequences are duplicated on both ends of the DNA molecule as a result of the mechanism that generated them
- 76REPLICATION concatemera long continuous DNA molecule that contains multiple copies of the same DNA sequence linked in series
- 77REPLICATION headful packaging- When T4 DNA is packaged into capsids, the concatemer is not cut at a specific sequence; instead linear segments of DNA just long enough to fill a phage head are generated
- common among bacteriophages - 78lytic cycle- Culminates in death of the host cell
- refers to last stage of infection where bacterium lyses & releases the phages produced within - 79Virulent phage:A phage that replicates only by a lytic cycle
- 80lysogenic cycle- phages coexist with host in a state called lysogeny
- allows replication of the phage genome without destroying the host - 81lysogenA cell that harbors a temperate virus
- 82Temperate phages:Phages capable of using both modes of replicating within a bacterium
- 83prophage- in lysogeny, temperate virus genome is integrated into bacterial chromosome or episome (plasmid)
- replicates w/host cell as long as repressor protein that activate the virulent pathway are repressed - 84if the phage repressor is inactivated or if its synthesis is in some way prevented, the prophage can be induced into the _____ stage. Various _____ conditions, especially damage to ..., can induce a prophage to enter the lytic pathway- lytic
- stressful
- host cell DNA - 85ANIMAL VIRUS INFECTION Many animal viruses have an _____ and RNA genome- envelope
- 86ANIMAL VIRUS INFECTION two key differences between bacterial and animal viruses are that- the entire virion of animal viruses (not just the nucleic acid) enters the host cell
- eukaryotic cells contain a nucleus, where many animal viruses replicate - 87ANIMAL VIRUS INFECTION virus receptors are typically animal cell surface proteins used in- cell–cell contact
- function in the immune system - 88ANIMAL VIRUS INFECTION In multicellular organisms, cells in different tissues or organs often express different proteins on their cell surfaces, thus viruses that infect animals often infect only _____ _____certain tissues
- 89ANIMAL VIRUS INFECTION entry into a host cell generally occurs by fusion with the _____ ______ or by _____- cytoplasmic membrane
- endocytosis - 90ANIMAL VIRUS INFECTION After entry into the cell, animal viruses must eventually lose their _____ _____ to deliver their genetic cargo to the ______- outer coat
- cytosol - 91ANIMAL VIRUS INFECTION Some enveloped viruses are uncoated at the host _____ _____, releasing the nucleocapsid into the cytoplasm, while other enveloped and _____ viruses entering via _____ are uncoated in the host cytoplasm- cytoplasmic membrane
- naked
- enveloped
- endocytosis - 92ANIMAL VIRUS INFECTION If the viral genome is DNA, the genome passes through in to the _____ for replication. Most RNA-based viruses are replicated or converted to DNA by viral enzymes within the _____- nucleus
- nucleocapsid - 93ANIMAL VIRUS INFECTION many animal viruses must be enveloped. this typically occurs when the virion exits the animal cell through _____ or _____ _____ where virus may pick up part of the cell’s _____ ______ as part of its envelope- budding
- cell lysis
- cytoplasmic membrane - 94ANIMAL VIRUS INFECTION If an animal virus initially evades the immune system, animal viruses can produce at least four different types of infections:- virulent infection
- latent infection
- persistent infections
- transformation - 95ANIMAL VIRUS INFECTION virulent infectionresults in lysis of the host cell; this is the most common outcome.
- 96ANIMAL VIRUS INFECTION latent infection- the viral DNA exists in the host’s genome and virions are not produced
- leaves the host cell unharmed unless and until an event triggers the virulent pathway - 97ANIMAL VIRUS INFECTION persistent infections- cell releases virions via budding
- slow process
- host cell may not be lysed, instead continues to grow and produce more virions - 98ANIMAL VIRUS INFECTION transformationcertain animal viruses can convert
a normal cell into a tumor cell - 99ANIMAL VIRUS INFECTION retroviruses- contain an RNA genome
- replicated inside the host cell via DNA intermediate that transfers information from RNA to DNA via reverse transcriptase - 100ANIMAL VIRUS INFECTION Retroviruses were the first viruses shown to cause the following two diseases:- cancer
- HIV - 101ANIMAL VIRUS INFECTION - Retroviruses are enveloped viruses and carry several enzymes within the virion: - as well as two identical _____ ______ RNAs of the _____ sense- reverse transcriptase, integrase, and a retroviral-specific protease
- single-stranded RNAs
- plus - 102ANIMAL VIRUS INFECTION - RETROVIRUS reverse transcription begins in the _____. ssDNA is produced and _____ ______ uses this as a template to make a complementary strand producing _____;- nucleocapsid
- reverse transcriptase
- dsDNA - 103ANIMAL VIRUS INFECTION - RETROVIRUS The dsDNA is released from the nucleocapsid and enters the host ____ along with the integrase and is incorporated into the host genome creating a _____- nucleus
- provirus - 104ANIMAL VIRUS INFECTION The provirus remains in the host ______ indefinitely, and can be transcribed by the host RNA polymerase to form more copies which _____ through the host cell & infect other cells- genome
- bud - 105BACTERIOPHAGE OR ANIMAL VIRUS Attachment: proteins on tails attach to proteins on cell wallBacteriophage
- 106BACTERIOPHAGE OR ANIMAL VIRUS Attachment: spikes, capsids, or envelope proteins attach to proteins or glycoproteins on cell membraneAnimal Virus
- 107BACTERIOPHAGE OR ANIMAL VIRUS Penetration: genome is injected into cell or diffuses into cellBacteriophage
- 108BACTERIOPHAGE OR ANIMAL VIRUS Penetration: capsid enters cell by direct penetration, fusion, or endocytosisAnimal Virus
- 109BACTERIOPHAGE OR ANIMAL VIRUS UncoatingAnimal Virus
- 110BACTERIOPHAGE OR ANIMAL VIRUS Site of synthesis is in the cytoplasmBacteriophage
- 111BACTERIOPHAGE OR ANIMAL VIRUS Site of synthesis of RNA viruses in cytoplasm; site of synthesis of DNA viruses in nucleusAnimal Virus
- 112BACTERIOPHAGE OR ANIMAL VIRUS Site of assembly in cytoplasmBacteriophage / Animal Virus
- 113BACTERIOPHAGE OR ANIMAL VIRUS Site of assembly of RNA viruses in cytoplasm and of DNA viruses in nucleusAnimal Virus
- 114BACTERIOPHAGE OR ANIMAL VIRUS Released through the mechanism lysisBacteriophage / Animal Virus
- 115BACTERIOPHAGE OR ANIMAL VIRUS Naked virons are released by exocytosis or lysis; enveloped virons are released by buddingAnimal Virus
- 116BACTERIOPHAGE OR ANIMAL VIRUS Nature of chronic infection: Lysogeny, always incorporated into host chromosome, may leave host chromosomeBacteriophage
- 117BACTERIOPHAGE OR ANIMAL VIRUS Nature of chronic infection: Latency, with or without incorporation into host DNA; incorporation is permanentAnimal Virus
- 118TOXIN-ANTITOXIN (TA) MODULESBacterial toxin-antitoxin (TA) modules encode a toxin protein capable of inhibiting cell growth and an antitoxin that counteracts the toxin
- 119TOXIN-ANTITOXIN (TA) MODULES majority of toxins are enzymes that interfere with _____ or ___ ______- translation
- DNA replication - 120TOXIN-ANTITOXIN (TA) MODULES Antitoxins are _____ or _____ that protect cell from their related toxins by ...- inhibiting translation of toxin mRNA
- or binding/inhibiting the toxin protein
- or by reversing its effect on the targets
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- (Exam III) Microbiology Fichas sobre Chapter 8: Viruses and Their Replication, creado por Alexandra Bozan el 07/04/2020.
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- Alexandra Bozan
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