chapter 13

genetic material of viruses

more variety than cells the cell is only dsDNA ; never use ssSNA or dsRNA viral g genome can be either DNA or RNA primary way to classify virus is by this method dsDNA, ssDNA, ssRNA, dsRNA= viral viral can be linear composed of several nucleic acid, circular or singular ex= influenza virus = 8 linear segments or ssRNA poliovirus= 1 molecule of ssRNA viral genomes normally smaller than cell genomes

culture virus in bacteria

most known about viral replication because bacteriophages are used and easy to culture because bacteria are easily grown and maintained either in liquid culture or agar plates - during incubation, bacteria are infected with the phage and lysed and release new phages that infect nearby bacteria while the uninfected bacteria grow and reproduce normally

oncogenes

their name when they are active how they can cause cancer - activity oncogenes - the inactivation of oncogene repressors ** several genetic changes must occur before cancer develops--> "multiple hits" of the genome inactive oncogene= "protooncogene"

plant infecting virus

they are less well known but were the first virus discovered and isolated from the tobacco plant Plant viruses infect food crops like corn, beans, sugarcane, tobacco, potatoes - they are introduced to plants through abrasions in the cell wall or by plant parasites (nematodes, aphids) after entry the virus follow the replication cycle

viral replication

they cannot reproduce by themselves because they lack the genes for the enzyme necessary for reproduction, they do not have functional ribosomes for protein synthesis - depend on the hosts enzymes/organelles to reproduce new virions - once the host cell falls under control the viral. genome, they are forced to replicate viral genetic material and translate viral proteins (viral capsomeres, viral enzymes) - replication cycle of a virus results inn the death/lysis of the host cell

how viruses differ

type of genetic material, kind of cells they attack, size, nature of their capsid coat, their shapes, presence/absence of an envelope

how naked animal viruses are released

(2 ways) 1. may be extruded from cell by exocytosis (similar to budding but without acquisition of an envelope) 2. may cause lysis and cell death

capsomeres

(capsomers) capsid of a virus composed of proteinaceous subunits some composed of 1 type of protein, others composed of several different kinds of proteins

Retroviruses

+ssRNA viruses that do not use their genome as mRNA rather reverse transcriptase is carried within the retroviruses capsid and transcribes a dsDNA intermediary from the +ssRNA genome by forming -DNA; which the complement of this is +DNA. which forms dsDNA (can be inserted. in. genome) DNA intermediary serves as a template for synthesis of additional +ssRNA molecules (which acts as both mRNA for protein. synthesis and as genomes for new virions) ex=HIV - do not use their genomes as mRNA, they use a DNA itnermediary transcribed by viral reverse transcriptase as template to produce viral genomes - enzyme good for diagnosing because can detect RNA product

oncogenes "hits"

- cancer does not result from a single mutation but from multiple first hit=. virus inserts promoter on an oncogene (leaving the gene for the repressor. alone); results in no cancerp-becaue still regulated by the repressor. that binds to the promoting region of the oncogene MOST VIRAL GENES ARE CONSITIUTIVE= CANNOT BE TURNED OFF second hit (exposure to virus or same virus continuously hits)= virus inserts into the repressor. gene. (while the. insert. on the promoter of oncogene is still there) ; results in cancer because now the cell is dividing and no repressor protein is being translated because the gene is segmented

virus novel properties

- insert macromolecules outside a cell but become active inside a cell - do not divide or grow -acellular -obligate intracellular parasites -contain either DNA or RNA -genome can be dsDNA, ssDNA, dsRNA, ssRNA, or ss-RNA, +ssRNA - usually ultramicroscopic. in size, ranging from. 10nm- to over 500nm -have a proteinaceous capsid around the genome; some have an envelope around the capsid -replicate in an assembly-line manner using the enzymes and organelles of a host cell

cells novel properties

- metabolize on their own - divide and grow -cellular - most are free living -contain both DNA and RNA -genome is dsDNA - 200nm - 12 cm in diameter -surrounded by a phospholipid membrane and often a cell wall -self-replicating by asexual or sexual means

why people resist concept of prions

- some resist the concept of prions because the particles lack any nucleic acid which violates the rule that protein synthesis occurs via translation of mRNA given prions lack nucleic acids how can they replicate themselves

13.4 Comparison of Bacteriophage and Animal Virus Replication

1. Bacteriophage attachment= proteins on tails attach to proteins on cell wall penetration=. genome is injected into cell or diffuses into cell uncoating= none site of synthesis= cytoplasm site of assembly= cytoplasm mechanism of release= lysis nature of chronic infection=. lysogeny, always incorporated into host chromosome, may leave host chromosome 2.Animal Virus attachment= spikes , capsids, or envelope proteins attach to proteins or glycoproteins on cell membrane penetration=. capsid enters. cell by direct penetration, membrane fusion, or endocytosis uncoating =removal of capsid by cell enzymes site of synthesis and assembly=RNA viruses = cytoplasm; DNA viruses= nucleus Mechanismof Release= naked virions; exocytosis or lysis and enveloped virions; budding nature of chronic infection= latency, with or without incorporation into host DNA; incorporation is permanent

examples of specific order, family, genus, epithet

1. HIV order= not assinged family= retrovirdae genus=lentivirus epithet=human immunodeficiency virus 2. Rabies virus order= mononegaavirales family=rhabdoviridae genus= Lyssavirus epithet= rabies virus

2 cell culture types

1. diploid cell culture 2. continuous cell culture

lysogeny shown with lambda phage

1. virion randomly contacts E.coli cell and attached with its tail 2. viral DNA enters the cell. but hosts DNA is not destroyed and the phage genome does not immediately take over the host cell therefore the virus remains inactive as a prophage 3. prophage remains inactive by coding for a protein that supresses its genes, the side effect of the repressor. protein is that it renders the bacterium resistant to additional infection by other viruses of the same type 4. prophage inserts its DNA into bacterium becoming a physical part of the bacterial chromosome (fusing 2 pieces of DNA ; the prophage and the host ) 5. every time the cell replicates its infected chromosome the prophage gets replicated, thus all daughter cells of lysogenic cell are infected with the inactive virus. - a prophage and their descendants may remain a part of the bacterial chromosome for generations or forever 6. induction can occur 7. after. induction the. lytic steps of synthesis 8.assembly 9. release resumes from where it was stopped when the prophage was inactive and the cell lyses and breaks open

viruses alive?

5 characteristics of life= growth, self reproduction, responsiveness, ability to metabolize, and within cell structures - viruses are not Alvie 4 reasons why people think viruses are parasites 1. sophisticated methods of invading cells 2. have means of taking control of host cell 3. possess genomes containing instructions for replicating themselves 4. evolve over time - possibly the least complex living entities. but outside of cells they are not alive but within cell they direct the synthesis and assembly required to make copies of themselves

prophage

A phage genome that has been inserted into a specific site on the bacterial chromosome. - it is INACTIVE in this stage. because it. codes for a repressor protein that inactive its genes

RNA dependent RNA polymerase

A viral enzyme that makes a strand of RNA by reading a strand of RNA . All prokaryotic and eukaryotic RNa polymerases are DNA dependent; they make a strand of RNa by reading a strand of DNA.=. opposite of the viral enzyme needed to make RNA from RNA - viruses that need this enzyme either bring it with them or it is the first thing that is transcribed and translated - enzyme makes complements to +ssRNA and the -ssRNA is used as a template to make more. +ssRNA copies -ssRNA needs this enzyme brought with it because the first thing it needs to do when gets into cell is to make complementary +ssRNA (used for transcription of viral proteins and. as template. to make more genome copies)

complex virus

A virus with a complicated structure, such as a bacteriophage. capsids of many different shapes that do not readily fit in either categories ex= smallpox virus with several covering layers (including lipid) and no easily identifiable capsid

synthesis T4

After loosing its chromosome, bacteria are unable to synthesize more of its own molecules and begins to synthesize only the viral parts because the cell is now under control of the viral genome - T4 dsDNA viruses, protein synthesis is straight forward because it is similar to the cellular processes in that the mRNA is transcribed from the VIRAL DNA , and the host ribosomes translate viral proteins (capsomeres, tail components, viral DNA polypeptides used to replicate viral DNA, and lysozyme - lysozyme in this stage is used to weaken. the cell wall from within which enables the virions to leave the cell a after assembling

virally induced human cancers

Burkett's lymphoma (EBV), Hodgkin's disease(EBV) , Kaposi's sarcoma(HIV), cervical cancer(HPV)

helical virus

Capsid composed of Capsomeres bonded together in a spiral arrangement to form a tube around the Nucleic Acid

Why are DNA viruses more likely to cause neoplasias than are RNA viruses?

DNA viruses are more likely to cause neoplasia compared to RNA viruses because DNA virus genomes are more likely to become integrated into the host genome, and insertion of foreign DNA can result in damage to host genes or regulatory structures, which may in turn result in the cell becoming precancerous.

Families of human viruses (chart 13.2)

DNA viruses-->family--> strand type--> representative genera (diseases) 1. Poxviridae= double= Orthopoxvirus (smallpox) 2.Herpesviridae= double=. simplex virus (herpes. type 1: fever blisters, respiratory. infections: type 2=. genital infections;;; Varicellovirus (chickenpox)= Lymphocrytovirus ;; Epstein-Barr virus (infectious mononucleosis;; Burkett's lymphoma;; cytomegalovirus (birth defects);;Roseolovirus (roseola causes rash; no vaccine) 3. Pappilomaviridae=. double= Papillommaavirus (benign tumors, warts, cervical and penile cancers; good reason to get males vaccinated ) 4. Polyommaviridae= double=Polyomavirus (progressive multifocal leukoencephaalopathy; WBC infiltrate the brain) 5. Adenoviridae= double= Mastadenovirus (conjunctivitis, respiratory infections) ; used in COVID vaccines as a delivery method because they do not cause bad reaction and cannot be replicated just deliver drugs for virus specifically 6. Hepadnaviridae= partial single and partial double=. Orthohepadnavirus (hepatitis B) 7. Parvoviridae= single=Erthrovirus (erythema infectiosum; causes childhood disease with specific rash)

budding

ENVELOPED animala viruses released via this process AS virions are assembled , they are extruded through one of the cells membranes (nuclear, ER, cytoplasmic) - each enveloped virion acquires portion of cells membrane into which viral proteins were inserted during synthesis stage: membrane becomes viral envelope - allows the infected cell. of amina to remain alive because it is not quickly lysed

synthesis of animal viruses

Each type of animal virus requires different strategy depending on its nucleic acid (ds, ss, DNA, RNA) DNA viruses often enter the nucleus RNA viruses often replicated in the cytoplasm when synthesizing envelope viruses, some viral proteins are inserted into the cell membrane and these membranes become to the viral envelope and the proteins become the envelopes spikes - each synthesis and assembly of animal virus must consider.. 1. how is mRNA synthesized that needed for translation of viral proteins 2.what molecule serves as. template for nucleic acid replication

burst time

For any phage undergoing LYTIC replication, the period of time required to complete the entire process, from attachment to release.

•Why are naked icosahedral viruses able to be crystallized?

Naked= do not have envelope. Can be crystalized because they are composed entirely of protein , that protein capsid can be crystallized - harder t o see on X ray Crystalography when have lipids and sugars

assembly T4

Not 100% known, but capsomeres accumulate within the cell, and spontaneously attach to each other forming new capsid heads - tails assemble and attach to heads, tail fibers attach to the tails forming the = MATURE VIRION this all occurs from spontaneous assembly with little to no enzymatic activity - used to be though capsid always formed. around the genome but some viruses inject genome into an already assembled capsid. --> ***** sometimes, the capsid. assembles around leftover DNA fragments of the hosts DNA not the viral DNA - transfers this DNA when leaves the cell to another bacterium resulting in horizontal transformation Called transduction

templating

P-prp acts as a template to refold molecule of c-Prp process= 1. cell make c-Prp and inserted into cells cytoplasmic membrane 2. incorrectly folded p-Prp may infect the brain or may be produced by altered c-Prp gene 3. prion protein (p-Prp) reacts with the c-Prp on the cell surface 4. p-Prp converts c-Prp to p-Prp 5. p-Prp molecule continue to convert normal c-Prp to p-Prp

Families of Human Viruses (chart 13.2)

RNA viruses-->family--> strand type-->Representative Genera( diseases ) 1. Picoornaviridae=single, +^a=. Enterovirus. (polio);l Hepatovirus (hepatitis A) 2.Caliciviridae= single,+. =Norovirus- stomach flu (gastroenteritis) 3. Astroviridae= single, +Astrovirus-stomach flu. (gastroenteritis ). 4. Hepeviridae=single,+=. Hepevirus(hepatitis E) 5. Togaviridae= single, +=. Alphavirus (encephalitis);; Rubivirus (rubella- German measles) 6. Flaviviridae= single, += Flaviviurs. (yellow fever,Japanese encephalitis) ; Hepacivirus (hepatitis C) 7. Coronaviridae= single, += Coronavirus (common cold, severe acute respiratory syndrome) 8.Retroviridae=. single, +, segmented =Deltaretrovirus(leukemia) and lentivirus(AIDS) 9. Orthomyxoviridae= single, -^b, segmented = Influenzavirus (flu) 10. Paramyxoviridae= single, -= Paramyxovirus (common cold, respiratory infections); Pneumoviurs (pneumonia, common cold); Morbillivirus(measles); Rubulavirus (mumps) 11. Rhabdoviridae.= single,- = Lyssavirus (rabies) 12. Bunyaviridae= single, -, segmented= Bunyavirus (California encephalitis virus); Hantavirus (pneumonia) 13. Filoviridae= single, -= Filovirus (Ebolaa hemorrhagic fever); Marburgvirus (hemorrhagic fever) 14. Arenaviridae=single, - , segmented= single, -, segmented= Lassavirus (hemorrhagic fever) 15. Reoviridae= Double,segmented. = Orbivirus (encephalitis) ; Rotavirus (diarrhea); Coltivirus (colorado tick fever)

replication of animal viruses

Same basic replication pathway as bacteriophages Differences result from Presence of envelope around some viruses--> only seen in animal viruses because prokaryotes or other cells infected have cell wall (extra barrier to cross). Eukaryotic nature of animal cells Lack of cell wall in animal cells--> means anything being breached occurs in the cells cytoplasmic membrane (do not need needle like way to get into cell) - this results in. differences of how viruses get into the host cell because they are infecting different type of cell

metastasis

The spread of cancer cells beyond their original site

Do viral genomes have promoters

Yes, anything that is getting transcribed has to have a promoter the RNA polymerase can bind to, therefore viral genomes have to have promoters to make viral proteins and mRNA

lysogenic conversion

a change in the properties of a bacterium conferred by a prophage when lysogenic phage changes the phenotype of a bacteria from harmless into pathogenic form - the bacteriophage genes are responsible for toxins and other diseases that evoke proteins found in bacteria agents such as diphtheria, cholera, rheumatic fever, and cases of E.coli causing diarrhea - creation of proteins

Lysogenic Replication cycle / lyosogeny

a modified replication cycle in which infected host cells grow and reproduce normally for a few generations before they lyse some bacteriophages have this -- lysogenic phages can change the phenotype of its bacteria

direct penetration

a process in which the viral capsid attaches and sinks into the cytoplasmic membrane, creating a pore through which the genome alone enters the cell, leaving empty capsid on the surface (some naked viruses enter this way). ex= poliovirus

DNA viruses in families that lead to cancer

adenoviridae, herpesviridae, hepadnaviridae, Papillomviridae, Polyomavirida, and 2. RNA viruses in family Retroviridae lead to these and other human cancers

Prp

all mammals brain cells contain cytoplasmic membrane protein called Prp it is anchored in the lipid. raft., playing role in normal. activity of the Brian (exact function not known) amino acid sequence of Prp = protein can fold in 2 stable tertiary. structures normal cellular (c-Prp) has prominent alpha helices ** diseases causing form prion (p-Prp) forms beta pleated sheets. this state causes normal c-Prp to misbehave and refold into p-Prp--> they convert r other than reproduce them; group into multimers (stable and resistant. to protease) --> as clumps of p-Prp propagate through the brain neurons do not work properly and die leaving holes and spongey appearance *************** PRP causes cellular proteins to misfold creating large empty spaces called vacuoles inside of the brain giving spongey appearance

difference between animals virus and phage

animal viruses receptors are chemically attracted to the host cells receptor so they do not come together spontaneously; do not have tails or tail fibers ; have glycoprotein spikes or other attachment molecules that mediate attachment ; has 3 mechanisms of entry (some include bringing in capsid and envelope) bacteriophages and their specific bacteria come together randomly when they collide ; they have tails and tail fibers ; only enters by injecting DNA

latency

animal viruses remain dormant in cells (AIDS, chicken pox, Hepatitis. B, herpes)

fungal viruses

appear to only exist in cells with no extracellular state cannot penetrate the thick cell walls but since fungi fuse their cells in their life cycle, viral infections can easily be propagated by fusion of an infected fungal cell with an uninfected one

why HPV vaccines have short window

as one gets older the chances of contracting it increase, and if only get one dose and is then exposed, it will not work, need both doses

endocytosis

attachment of the virus to the receptor molecule on a cell surface that stimulates cello endocytize the entire virus including the envelope, capsid, and any proteins attached most enveloped viruses (herpes) do this and some naked viruses (adenovirus) this method IS NOT USED by those species that have a cell wall (specific to animal viruses) because the wall is too rigid ********** BUT cells do not endocytosize, the virus gets ends by the cell and now has to get out of the endocytotic vesicle and. the genome must be uncoated FdsD

lytic replication cycle

attachment of virion to the host cell entry of virion or its genome into host cell synthesis of new nucleic acid and viral proteins by host cells enzymes and ribosomes assembly of new virions within the host cell release of new virions from the host cell

Why are DNA viruses more likely to cause neoplasias than are RNA viruses?

because DNA viruses can get inserted into the host chromosome. whereas RNA viruses cannot. Therefore, the DAN virus can be inserted at different locations that increase the chance of causing neoplasais (insert at oncogene and repressor protein) which can cause Since RNA viruses cannot enter the host chromosome because it is RNA and the chromosome is composed of DNA, it gets induced and excised from the host chromosome and is not permanently incorporated like the DNA viruses are. Once they are inserted they are latent proviruses

Since RNA does. not. incorporate directly. in chromosome molecule, how does ssRNA of HIV become provirus incorporated in the host DNA?

because like all retroviruses they have reverse transcriptase which transcribes genetic information of the +RNA molecule into a DNA molecule which then gets incorporated into the hosts genome.

Treatment = difficult bc...

because viral replication uses cellular. structures and pathways involved in growth and maintenance of healthy cells, any treatment strategy of viral diseases involving disrupting the viral replication may disrupt normal cell processes

disease associated with prions

bovine spongiform encephalitis (BSE) = mad cow disease; can spread from cattle to people if people. eat meat from a. cow that has BSE in their tissues--> causes vCJD scarpie= sheet kuru= human disease that has been eliminated (laughing till their death by eating dead families brain) chronic wasting disease (CWD)- in deer and elk; abnormal. behavior, loose bodily functions and die variant Crutzfeldt-Jaakob disease (vCJD)= in humans affects cerebrum by causing vacuole holes. and amyloid plauques, clusters of prion proteins (some people think noninfectious prions are involved in AD, PD, and amyotrophic lateral sclerosis. (ALS), and some cancer

prion disease

can be inherited., sporadic, or infectious 1. inherited= mutation in the c-Prp gene results in the initial formation of p-Prp 2. sporadic prion disease= develops from rare, random changes of c-Prp in membrane to p-Prp. (the change is in the protein shape; Prp gene remains normal) 3. infectious prion disease= ingestion of infected tissue, transplants of infected tissue, or contact between infected tissue and the mucous member or skin abrasion - generally prions only infect. related hosts, some can jump species

culturing viruses in a lab

cannot be grown In standard agar or broth because cannot metabolize or replicate by themselves; must be cultured inside suitable host cell which is complicates detection/identification/characterization 3 types of media used 1. consisting of mature organisms. (bacteria, plants, animals) 2. embryonate (fertilized eggs) 3. cell cultures

plaques

clear zone that interrupt uniform bacterial lawn, representing the areas where phages lysed bacteria

plant diseases

coconut palm, chrysanthemum, potato, cucumber, avocado

latency with lysogeny

condition is permanent when latent animal viruses incorporate their genome in the hosts DNA because the induction process does NOT occur it becomes permanent and physical part of the hosts chromosome and all descendants of the infected cell will carry the provirus _____ RNA viruses cannot. do this because RNA is not DNA and the host chromosome is made. of DNA so it cannot be incorporated. also retroviruses are the only ones who can because they create a dsDNA intermediary that can be inserted

cell culture

consists of cells isolated from an organism and grown on the surface of a medium or in broth - practical when antibiotics are provided as a way to limit growth of contaminating bacteria less expensive than maintaining research animals, plants, eggs, avoids moral problems - sometimes called a tissue culture but cell cultures are more accurate because there is only. a single type of cell used in a culture and the definition of a tissue is composed of at least 2 types of cells -cell culture media is always pink or red because it is used as a pH indicator.--> as the cells metabolize, the medium turns orange but if it turns yellow, the cells are dead because they produced too many waste products

environmental factors contribution

contribute to the inhibition oncogene repressors and activation of the oncogenes ex= UV light, radiation, chemicals, viruses = carcinogens viruses contribute to the development of 20-25% of human cancers

prion deactivation

cooking does not deactivate prions and neither do normal sterilization processes takes very high heat = 482C heat for hours or autoclaving at 132C in NaOH for 1 hour treatment with 10% solution of some phenolics for 1 hour enzyme "prionzyme" remove prions from medical equipment

diploid cell culture

created from embryonic animal, plant, or human cells that have been isolated and provided appropriate growth conditions cells cannot last more than 100 generations/cell divisions before they die

viral replication goal

dependent on hosts organelles and enzymes to create new virions 2 life cycles = lytic and lysogenic. bacteriophages and animal viruses use these except lysogenic is latent in animal viruses because no induction

Attachment of Animal Virus

dependent on the chemical attraction and exact fit between the attachment molecule on the virion and complementary receptors on the animal cell surface. (Animal phages lack tails and tail fibers BUT animal phages have glycoprotein spikes on the capsids of envelopes)

synthesis of RNA viruses in animals

differs significantly from cellular processes and from DNA replication. because cells do not have RNA genes 4 types of RNA viruses 1. +sense ssRNA 2. retroviruses 3. - sense ssRNA 4. dsRNA

•Why are viruses seemingly alive and yet not alive?

do not grow do not metabolize require different organism to replicate and do life cycle and functions

lytic replication of Bacteriophage T4

dsDNA phage of E. coli (T4) virion= complex with polyhedral head and helical tails seen in bacteriophages

outermost layer of the virion

either capsid or envelope provides virus protection. and recognition sites that bind to complementary chemicals on surfaces of specific host cells - once the virus is inside in the intracellular state the infection is initiated and the capsid and envelope is removed virus without a capsid exists as nucleic acid but is still considered a virus

membranes

embryonic tissues that provide ideal inoculation sites for growing viruses inject virus samples into the embryonate egg act sites best suited for particular viruses replication

viroids

extremely small (239 nucleotides), circular pieces of ssRNA that are infectious and pathogenic in plants - similar to RNA viruses except LACK CAPSIDS and viroids RNA do not code for proteins cause disease by adhering to complementary sequence of plant mRNA- forming a double strand RNA which plant enzyme degrades as if it were a dsRNA virus - diseased state because plant enzyme is destroying tis own mRNA - causes small potatoes

membrane fusion

fusion of the viral envelope with the hosts cytoplasmic membrane (must have an envelope. or else there would be nothing to fuse to) entire capsid and its contents enter the host cell when the viral envelope and host cytoplasmic membrane fuse, the releasing of the capsid occurs via UNCOATING getting into the cell cytoplasm while leaving the glycoproteins as part of the cell membrane (they do not enter the cell) ex= measles virus

protooncogenes

genes that promote cell growth and division as long as they are appropriately expressed under controlled conditions no cancer results

chart 13.3 Synthesis Strategies of Animal Viruses

genome-->How is mRNA synthesized--> What molecule is the template for genome replication? 1. dsDNA--> typicallyby cellularRNA polymerase (in nucleus) or by viral RNA polymerase in cytoplasm--> E/ strand serves as a template for its complement (except hepatitis B the synthesizes RNA to act as DNA) 2. ssDNA-->By RNA polymerase (in nucleus of cell)--> Complementary strand of DNA is synthesized to act as template 3. +ssRNA--> genome acts as mRNA. --> -RNA complementary to the genome is synthesized to act as template 4. +ssRNA (retroviridae)-->DNA is synthesized from RNA by reverse transcriptase; mRNA is transcribed from DNA by RNA polymerase--> DNA 5. -ssRNA-->By RNA dependent RNA transcriptase--> +RNA (mRNA) complementary to the genome 6. dsRNA--> Positive strand of genome acts as mRNA--> Each strand of genome acts as template for its compliment

- sense ssRNA viruses

have - genomes that must overcome the problem of: in order to synthesize a protein, cells ribosomes can only. use mRNA (mRNA is. + sense) . Ribosomes cannot recognize -ssRNA Overcomes: carrying within the capsid the enzyme "RNA dependent RNA transcriptase" which is released into the host cells cytoplasm during uncoating and than transcribes +ssRNA molecules from the viruses -ssRNA genome. Translation of protein can then occur as usual. Newly transcribed +ssRNA serves as a template for transcription of additional copies of -ssRNA ex= rabies and flu viruses

RNA virus/ enveloped virus

have variations on. the lytic and lysogenic cycles

transduction

horizontal gene transfer by means of viruses; the capsid may take up fragments of degraded host DNA instead of the replicated viral genome General transduction= carried out by lytic phages specialized transduction = carried out by lysogenic phages bc of the way the genome is handled inside the cell.

culturing viruses in embryonate chicken eggs

inexpensive, largest of cells, free containing microbes, contain nourishing mold (self sufficient) most suitable= checking eggs that have been. fertilized with a developing embryo vaccines for some viruses are prepared in chicken eggs; why asked if allergic to eggs at vaccine site because might be contaminated - have different places to inject viruses that results in different cell types JB lab. experiment - grew chlamydia; inject embroys and wait, take embryo out, cut off their head, cut it into pieces, and put it on. a cell dish

Persistent Infections

infections with enveloped viruses in which host cells shed viruses slowly and relatively steadily - the curve showing the virus abundance overtime lacks the burst of new virions seen in the lytic replication cycles -same beginning but released very steadily overtime.

viroid like agents

infectious, pathogenic RNA particles, lacking capsids but do not infect plants (why not Called viroids) they affect some fungi (no animal disease is known to be caused by these) possible that some infectious RNA may be responsible for human disease

Malignant Tumor

invade neighboring. tissues and travel through the body to invade other organs and tissues producing new tumors aka=cancers the cancers rob cells of space and nutrients and cause pain ; in some cancers, the malignant cells derange function of affected tissues until the body cannot withstand loss of normal function and dies

complex bacteriophage capsid

isohedral heads that contain the genome, attached to helical tail with tail fibers

viral envelope

lack cell membrane, some (mainly animal viruses). have envelopes with similar composition to cell membranes surrounding their capsids

Latent Viruses/proviruses

latency can be prolonged with no viral activity signs or symptoms for years some latent viruses do not get incorporated into the host chromosome

continuous cell culture

longer lasting, derived from tumor cells. provide a never ending supply of new cells neoplastic cells divide relentlessly HeLa cells - from Henrietta Lacks ; she died from cervical cancer but her cells are still living in labs -HeLa cells have lost original. characteristics and are no longer diploid. because lost many chromosomes--> so now they provide only a semistandard human tissue culture medium for. studies on cell metabolism, aging, and viral infection

Why are lysogenic and latent viral infections generally longer lasting than lytic infections?

lysogneic and latent viral infections are longer lasting because lysogenic gets incorporated into the host chromosome and may not by induced at all or until several regenerations of the original cell. Latent viral infections are permanent , they re dormant for a while before they bring out infection. making them longer lasting. Lytic immediately goes from step to step without any period of not acting out their viral replication

generalists

many infect many kinds of cells or different hosts ex= West Nile Virus- can infect humans, birds, some reptiles, several mammalian species ** viruses can infect archaea, bacterial, plant, animal, fungal cells ; even tiny viruses can attack larger viruses

tumor

mass of neoplastic cells

virus

minuscule, acellular, infectious agents having 1 or. several pieces of nucleic acid (DNA or RNA) = genome Acellular; they have no cytoplasmic membrane (some possess an envelope) lack cytosol or functional organelles are not capable of metabolic activity on their own--> once they invade a cell, take control of the cells metabolism to produce more molecules of viral nucleic acid, viral proteins to assemble new viurses have extra and intracellular states

treatment for prion disease

no treatment for PD possible antimalarial drug "quinacrine" antipsychotic drug "chlorpromazine" antihistamine "astemizole" antibiotics against p-Prp problem is it must be performed on humans to see if it is effective or safe ------- p-Prp prions differ across species as seen in the BSE epidemic In. Great Britain ; resulting in the spread of prions from cattle. to humans who are infected beef from. cattle that. fed on nervous tissue of infected sheep

roles of viruses in cancer

normally, the division of cells in mature, multinucleate animal is under strict genetic control. -- genes. dictate that some cells do not divide at all. and those dividing are prevented. from unlimited division. Genes for cell division are turned on and off or in combination of both --- ** when something upsets the genetic control, the cells divide uncontrollably

intracellular state

not referred to as a virion it is just the nucleic acid that was inside the virus

burst size

number of virions released from each lysed bacterial cell graph= y axis= number infectious virions in the medium (log) x axis= time mins at0 minutes the # of virions is at log scale of 1 this represents the attachment of the virus to the cell decreases in size # back to 0 upon entry remains steady here during. synthesis and assembly spikes at the burst time. because it is releasing new virions out of the cell and once remains back steady it is stil high in # this is burst size ** characteristic of viruses that is well studied estimating the # of virions created per virus**

uncoating

occurs by. different means in different viruses ;some uncoat within vesicles created by cellular enzymes and others uncoated by enzymes within the cells cytosol - this is needed for viruses that penetrate the cell with their capsid still intact, it has to be removed to release the genome before replication of the virus can occur

entry mechanism

once inside, the T4 ohage either has enzymes that degrade the host DNA or the enzymes are the first proteins to be translated from genome

assmebly and release of animal viruses

once synthesis is complete, they assemble into virions that. are then released from. the host cell - most DNA viruses are assembled and released. from. the nucleus into the cytosol - most RNA viruses are developed solely in the cytoplasm

entry T4

once the T4 phage has attached to the bacterium cell wall, they mist overcome the barrier posed by the cell wall. and membrane to get into the cell upon contact with E.coli T4 releases LYSOZYME -- the phages tail sheath can then contract, forcing internal hollow tube within the tail of the cell wall/membrane - phage then injects its genome through tube into bacterium the empty capsid is left outside of the cell -after entry, viral enzymes that are carried within the capsid are delivered with the viral genome or are coded by viral genes and made by the bacterium - ENZYMES degrade the hosts DNA into constituent nucleotides

matrix proteins

other viral proteins fill region between capsid and envelope

unwinding of viral dsDNA

our cells. response to dsDNA is. to degrade it (importance of microRNA) so first needs to be unwinded into complements (+ssRNA and -ssRNA); both of these strands are used as templates to make the complement to end up with dsDNA - also needs RNA dep RNA poly encoded because it is used to make complementary RNA Astrnads

virion

outside of the cell in extracellular. state. consists of a capsid, surrounding the nucleic acid core so it is complete virus

•What characteristics of the genomes of parvoviruses and of reoviruses make them very different from cells?

parvovirus is single strand DN reoviruses is double stranded RNA both of these we do not have in our cells

1. Attachment T4

phages like all virions are nonmotile, contact with bacteria occurs from random collisions tail fibers= responsible for the attachment of the T4 to the host bacterium; the attachment proteins the tail fibers fit to complementary receptor proteins on the surface of the cell wall of E.coli -- various bacteriophages may attach to the receptor proteins on the hosts cell walls, flagella, or pilli phage attachment= very specific, might only infect on kind of bacterial species - uses this attachment for. bacterial identification in lab (phage typing)

temperate /lysogenic phages

phages that participate in both the lytic and lysogenic life cycel. phages. that are release and in the lysogenic replication cycle-------- phage attaches to host cell and penetrates host injecting DNA; in temperate bacteriophages Lange DNA forms circle either replicating/ transcribed to produce phage components in lytic cycle directing host celll to synthesize viral components; or it can go into the lysogenic cycle. lysogenic cycle= phage DNA integrates within bacterial chromosome by remcobination ; inserted DNA = prophage (most repressed by repressor proteins products go prophage gene; copies with host chromosome) ; Cana be induced or not ex= occurs in lambda hage (another parasite of. E.coli) lambda has linear molecule of dsDNA and complex capsid with icosahedral heat attached to a tail with no tail fibers

envelope

phospholipid membrane surrounding neucleocapsid that some virions have

induction

process where the prophage is excised from the hosts chromosome by recombination or some other genetic event - they then can enter the lytic phase which results in synthesis, assembly, and release (cell death - no bacteria DNA gets excised just prophage, thereby becoming inactive caused by inductive agents

capsid

protein coat surrounding the nucleic acid core providing protection and giving the virus a means to attach to a host cell

lysozyme

protein enzyme that is carried within the capsid that weakens the peptidoglycan

prions

proteinaceous infective particles; agent different from any known infectious agent lacking instructional nucleic acids - before discovered, people though prions were "slow viruses" because can take 60 years after infection for symptoms and on set to occur not viruses because they lack nucleic acids

sizes of virus

range but normally very small can be a megavirus= 500nm diameter, which is the size of a bacterial cell normally

culturing viruses in plants and animals

rats, mice, guinea pigs, rabbits, pigs are animals used - maintaining lab animals can be difficult and expensive and raises ethical issues alternative =. using fertilized chicken eggs or cell cultures

benign tumors

remain in one place and are not harmful sometimes they are painful and take space and nutrients from adjacent cells

theories proposed to explain the role of viruses play in cancer development...

revolve around protooncogenes

polyhedral virus

roughly spherical, with a shape similar to a geodesic dome (common type of polyhedral capsid= ICOSAHEDRON with 20 sides )

indicative agents

same physical and chemical agents that damage DNA - UV light, X rays, carcinogenic chemicals. this can trigger induction to occur which can be advantageous to the virus because now they can synthesize, assemble, and release.

synthesis of ssDNA viruses

seen in human parvovirus - cellular RNA polymerase synthesizes mRNA complementary to viral ssDNA and cellular ribosomes can translate viral protein forming a dsDNA molecule; used for viral replication and transcription (cells do not have ssDNA so require unique form of DNA replication) PARVOVIRUS - ssDNA of this virus folds onto itself to form a hairpin loop that acts as dsDNA; can be replicated by cellular DNA polymerase the cellular polymerase replicates this "false" dsDNA and newly replicated strands of DNA is released as ssDNA and ssDNA packed into viral capsid.

viral shapes

shapes of virions are used to classify viruses 3 basic viral shapes = helical, polyhedral, and complex

Dmitri Ivanowski

showed viruses were acellular through an. experiment. designed to show the cause of tobacco mosaic disease - filtered sap of infected tobacco plants through porcelain filter that is fine enough to trap even the smallest of cells viruses are not. trapped so it gets passed into the liquid. remaining infectious to the tobacco plant prove the existence of acellular disease causing entity smaller than a bacterium TMV= tobacco mosaic virus was than isolated and characterized by Wendell. Stanley the electron microscope allowed scientists to see viruses

virus contribution to cancer

some viruses can carry copies of oncogenes as part of the genome --> others insert near to and promote oncogenes already present in the host -- can interfere with normal tumor repression when they insert into repressor genes (as latent proviruses)

synthesis of dsDNA animal viruses

synthesis of this virion is similar to normal replication of cellular DNA and normal translation of cellular proteins - dsDNA virus genome gets inside and cellular enzymes replication viral genome in same manner... -using viral DNA strand as template for its complement mRNA is transcribed from viral DNA in nucleus and exported to the cytoplasm where host ribosomes make capsomere proteins capsomeres then enter nucleus where new virions spontaneously assemble EXCEPTION = hepatitis B - genome replicated using RNA intermediary instead of replicating DNA from DNA template; first transcribed to mRNA used as a template used to make viral DNA copies of the genome --- latter process of transcription is the. reverse of the normal which is mediated by the enzyme reverse transcriptase

spike protein on host pm

the glycoproteins and spike proteins are translated by the virus and get trafficked to the hosts pm and stick out - when t he capsid pushes itself out of the membrane, pinches off taking some of the membrane with the glycoproteins

assembly mechanism

the hypothesis is that there are so many different parts of the virus (tail, base, tail sheath, capsid head) that they all spontaneously. come together and assemble - either the capsid spontaneously forms around the DNA or the DNA gets injected into the already assembled capsid

vaccine target

the spike proteins or glycoproteins that viruses use to get inside of the cell

Type/ # of virus released

the type and number of virus produced and released depends on 1. the type of virus 2. size/initial health of the host cell - animal viruses take longer to replicate compared to bacteriophages

classification of viruses

type of nucleic acid present, presence of an envelope, shape, size sstabalihsed families but only has 7 orders they do not describe a kingdom, division, class because relationships among viruses are not well understood family names are derived from special characteristics of viruses within families or from the name of an important member of the family epithets= italicized

neoplasia

uncontrolled cell division in multicellular animal forms neoplastic cells

why don't prions develop in all mammals because they have Prp?

under normal conditions, only other nearby proteins and polysaccharides in lipid rafts in cytoplasmic membrane force Prp in correct c-shape Human Prp misfolds ONLY if it contains methionine at the 129th amino acid - 40% humans have amino acid at this place in c-Prpand makes them susceptible to prion disease

dsRNA virus

unwinds into +ssRNA and -ssRNA +ssRNA molecule= mRNA for translation proteins; one protein it translates is RNA polymerase that transcribes dsRNA Each strand acts as a template for transcription. of its opposite which similar to that of DNA replication in cells causes diarrhea in infants

Adenovirus in vaccines

used as vectors in vaccines of COVID they do not replicate inside of the body they are packaged with dsDNA that encodes for the spike protein for sars COVID 19. adenovirus is used as a deliver mechanism for genetic material, allowing our bodies to make mRNA copies to create the protein that our immune system will respond to.

viral hosts

very specific due to the precise affinity of viral attachment molecule (the proteins or glycoproteins that are on the viral surface) for complementary proteins/glycoproteins on the surface of the host cell ex= HIV specifically attacks. the helper T lymphocytes (type of WBC) in humans it does not effect on human bone or muscle cells

Positive sense ssRNA

viral RNA that can act as mRNA ; ribosome can translate polypeptide directly form +ssRNA - ss viral RNA that can act directly as mRNA ribosomes can translate polypeptide using codons of these RNAs (ex=poliovirus) -- in many +ssRNA virally coded RNA polymerase transcribes complementary -ssRNA from the +ssRNA genome The -ssRNA is a template for transcription of multiple +ssRNA genomes --> this is unique to viruses because no cell transcribes RNA from RNA

nucleocapsid

viral nucleic acid and its capsid can crystalize like crystalline chemicals

enveloped virus

virion with a membrane provides some protection to. virus from immune system because they carry membrane of the host cell that is chemically similar are more fragile than naked because they are susceptible to detergents, alcohol, and drying out - enveloped virus acquires envelope form the host cell during viral replication or release ; composed of phospholipid bilayer and proteins however some proteins are virally coded glycoproteins (appear as SPIKES) protruding outward from the cells surface- these get recognized by the specific receptor on host cell *** envelopes proteins and glycoproteins play a role in virion recognition of host cells

non enveloped/. naked virus

virion without a membrane more stable outside host but expose more viral proteins to the environment and are more susceptible to being recognized by the immune system once inside of a host

release T4

virions are released was lysozyme completes working on the cell wall bacterium disintegrates and the appearance of plaques on a lawn show this disintegration --- for the phage T4the lytic replication takes. 25 minutes can produce 100-200 new virions for each singular cell that is lysed

Entry/ Uncoating of animal viruses

virus enters the host cell shortly after attachment 3 different mechanisms of. entry. 1. direct penetration 2. membrane fusion 3. endocytosis.

bacteriophage

virus that infects bacteria "phage" greater number of bacteriophages than all bacteria, archaea, eukaryotes put together

bacteriophage attachment

viruses are not alive, they cannot move towards the host cell to attach, the means is completely random the attachment proteins are on the tail fibers have enzyme lysozyme and DNA packaged in the capsid the tail sheath inserts hollow tube allowing for the genetic material to go into the host cell once lysozyme weakens the cell wall

capsid morphology

viruses in the extracellular state only have a capsid (virions)

acellular agents

viruses, viroids, prions that are infectious in humans, animals, plants, bacteria. simple compared to a cell--> they lack cytoplasmic membrane, composed of few organic molecules, lack cell structure, lack. most characteristics of life --> cannot cary out any metabolic pathway, cannot grow or respond to the environment , cannot reproduce independently, have to use the chemical and physical structural components of cells they infect use the host cells metabolic pathway to increase their number

Peyton Rous

was involved in the discovery of the role of viruses in the transmission of certain types of cancer.

plaque assay

way for virologists to establish phage numbers they assume that each plaque corresponds to a single phage spreading and multiplying though the original bacterium / virus mixture

spongiform encephalopathies

what a prion diseased brain is called

bacteria in depth (13.5)

width= 200-2000nm length=200-550,000 nm nucleic acid= both DNA and RNA protein= present. cellular cytoplasmic membrane has functional ribosomes grows self replicative responsiveness metabolism

viroids in depth (13.5)

width= 2nm length=40-130nm RNA only no protein not cellular no cytoplasmic membrane no functional ribosomes no growth not self replication no responsiveness no metabolism

prions in depth (13.5)

width= 5nm length=5nm nucleic acid=. none Prp protein not cellular no cytoplasmic membrane no functional ribosomes no growth no self replicating but transforms Prp protein already present in cell no responsivenss no metabolism

viruses in depth (13.5)

width=10-400nm length=. 20-800nm nucleic acid= either DNA or RNA never both proteins present no cytoplasmic membrane not cellular no functional ribosomes no growth not self replicating responsiveness= some bacteriophages response. to a host cell by injecting their genomes no metabolism

do viral genomes have an origin of replication?

yes only DNA not RNA bc RNA is not being transcribed Need an origin of replication for dsDNA otherwise it cannot make copies