Microbiology Ch. 13
resistance and destruction of prions
- resistant to normal sterilization procedure like boiling or irradiating materials = infectious proteins - use incinerator, higher autoclave or chemicals that break the peptide bond
2 modes of attachment by animal virus
1) Adenovirus: icosahedral virus where the attachment site are small fibers at corner of icosahedron 2) enveloped (influenza) virus: attach at spikes on surface of envelope; complete attachment when many sites are bound
Bacteriophage replication steps
1) Attachment: phage attaches to host cell 2) Penetration: phage penetrates host cell and injects its DNA 3) Biosynthesis: phage DNA directs synthesis of viral components by the host cell 4) Maturation: viral components are assembled into virions 5) Release: host cell lyses and new virions are released
Diseases due to prions
1) CJD 2) Kuru 3) scraple = sheep CNS disease 4) mad cow disease 5) fatal insomnia 6) G-S-S syndrome
2 modes of release by animal virus
1) enveloped virus = BUDDING = nucleocapsid form envelope with viral receptor from host cell membrane = doesn't kill host cell immediately; sometimes host cell survives 2) nonenveloped = HOST CELL LYSIS = used by naked and complex virus; cytolytic virus = lyse host cell membrane
lytic cycle and lysogenic cycle
1) originally lineal phage DNA forms a circle 2) circle can multiply and be transcribed = production of new phage and cell lysis = lytic cycle OR 2) circle recombine with and become part of circular bacterial DNA = lysogenic cycle - inserted page = prophage
inhibiting retroviridae
1) reverse transcriptase = prevent (+) RNA strand -> dsDNA - degrades original viral RNA into host cell as provirus - never comes out of chromosome = HIV protected from IS and antiviral drug 2) integrase = vira DNA not incorporated in host cell chromosome 3) protease = polypeptide not cleaved to release structural capsid and functional enzyme proteins
What is the usual size range of viruses?
30 to 300 nanometers
polyhedral/icosahedral virus
3D, 20 sided - naked = adenovirus, poliovirus - enveloped = hep B
To what does the term viral species refer?
A group of viruses sharing the same genetic information and structure and ecological niche - common names used for species ex: HIV
List the four properties that define a virus. What is a virion?
A virus 1) contains DNA or RNA; 2) has a protein coat surrounding the nucleic acid; 3) multiplies inside a living cell using the synthetic machinery of the cell; and 4) causes the synthesis of virions. A virion is a fully developed virus particle that transfers the viral nucleic acid to another cell and initiates multiplication.
Which of the following viruses may cause a persistent viral infection? A. Measles virus B. HTLV-1 C. Varicellovirus D. Herpes simplex 1
A. Measles virus -persistent viral infection (or chronic viral infection) occurs gradually over a long period and fatal. - insert nucleic acid into host chromosome (provirus) or nucleic acid remains in repressed state in cytoplasm ex: liver cancer
Which statement concerning viral structure is true? A. Spikes are found on some viruses. They are very consistent in structure within a viral species and can be used for identification. B. The proteins in the envelope are capsomeres. C. All viruses contain an envelope, which is made of lipid, carbohydrate, and protein. D. Animal viruses usually contain tail sheaths and spikes
A. Spikes are found on some viruses. They are very consistent in structure within a viral species and can be used for identification. - Some enveloped viruses have spikes, and they can be used for identification, such as the H and N spikes on the influenza virus.
Which of the following statements concerning viruses is true? A. The "host range" for a virus is determined by the presence or absence of particular components on the surface of a host cell that are required for the virus to attach. B. Viruses contain both DNA and RNA, and they undergo binary fusion. C. Viruses are usually about the same size as bacteria. D. Viruses possess enzymes for protein synthesis and ATP generation.
A. The "host range" for a virus is determined by the presence or absence of particular components on the surface of a host cell that are required for the virus to attach. - Attachment of the virus to the host cell (the first step in the viral replication cycle) requires binding of complementary molecules on the virus and host cell.
Which of the following is NOT characteristic of viruses? A. Viral nucleic acid is surrounded by a plasma membrane. B. Viruses lack an ATP-generating mechanism. C. Viruses have either DNA or RNA but not both. D. Viruses are unaffected by antibiotics.
A. Viral nucleic acid is surrounded by a plasma membrane. - Viruses, just like prokaryotes, do NOT contain membrane enclosed organelles.
Which of the following pairs is NOT correctly matched? A. Viroid: infectious DNA B. Prion: infectious protein C. Latent viral infection: an inactive virus D. Persistent infection: an infection lasting E. months or years
A. Viroid: infectious DNA - Viroids are infectious pieces of RNA that cause some plant diseases, such as potato spindle tuber disease.
Some antibiotics activate phage genes. MRSA releasing Panton-Valentine leukocidin causes a life-threatening disease. Why can this happen following antibiotic treatment?
Antibiotic treatment of S. aureus can activate phage genes that encode P-V leukocidin.
Which of the following are possible strategies for treating viral infections? A. Blocking uncoating of the virus after entry B. All of the listed strategies are correct. C. Blocking biosynthesis of viral nucleic acids D. Blocking viral attachment to host cell receptors E. Blocking insertion of viral DNA into the host cell chromosomes
B. All of the listed strategies are correct. - A virus needs live host cells but must stop synthesis of host proteins, so the viral genes are translated.
Which of these viruses is known to cause a persistent viral infection? A. Varicellovirus B. Measles virus C. Herpes simplex virus D. Hepatitis A virus
B. Measles virus - can be responsible for a rare form of encephalitis called subacute sclerosing panencephalitis (SSPE) - most persistent viral infections, detectable infectious virus gradually builds up over a long period, rather than appearing suddenly like a latent viral infection
Which statement about viruses is FALSE? A. Viruses are active only when inside a cell. B. Viruses will usually infect any available cell, regardless of the cell type. C. Viruses always have a protein coat. D. The genome of a virus can be either DNA or RNA, depending on the particular virus.
B. Viruses will usually infect any available cell, regardless of the cell type. - host range of a virus is the spectrum of host cells the virus can infect. - There are viruses that infect invertebrates, vertebrates, plants, protists, fungi, and bacteria. However, most viruses are able to infect specific types of cells of only one host species.
Compare biosynthesis of a + stranded RNA and a − stranded RNA virus
Both produce double-stranded RNA, with the - strand being the template for more + strands. + strands act as mRNA in both virus groups.
Some viruses leave a cell by pushing through the cell membrane (rather than lysing the cell). When this happens, a portion of the membrane wraps around the viral capsid, becoming the envelope. What is the name for this process?
Budding - process where envelope develops around the capsid - doesn't kill host cell immediately
Which method CANNOT be used to culture viruses in a laboratory? A. Tissue culture B. Live animals C. Nutrient agar culture medium D. Embryonated eggs E. Primates
C. Nutrient agar culture medium - 3 methods used in lab for culturing animal viruses = living animals, embryonated eggs or cell cultures
Which of these viruses can incorporate the molecule serving as mRNA into its capsid? A. Herpesvirus B. Rhabdovirus C. Picornavirus D. Poxvirus
C. Picornavirus - the + strands made in the picornavirus may serve as mRNA for translation of capsid proteins, may become incorporated into capsid proteins to form a new virus or serve as a template for continued RNA multiplication - once viral RNA and viral protein are synthesized, maturation occurs
Which of these processes of viral multiplication is most likely to damage the host cell? A. Uncoating B. Viral entry into host cells by fusion C. Release of nonenveloped viruses D. Reverse transcription of retroviral RNA E. Release of enveloped viruses
C. Release of nonenveloped viruses - nonenveloped viruses are released through ruptures in the host cell PM = leads to cell death of host cell
Which of the following is NOT an oncolytic virus? A. Adenovirus B. Vaccinia Virus C. Retrovirus D. Simplexvirus
C. Retrovirus - Oncolytic viruses infect and lyse cancer cells and include adenovirus, vaccinia virus, and simplexvirus.
Which of the following statements about viral spikes is FALSE? A. They are composed of carbohydrate-protein complexes. B. They are used for attachment. C. They are found only on nonenveloped viruses. D. They may cause hemagglutination. E. They bind to receptors on the host cell surface.
C. They are found only on nonenveloped viruses.
Which of the following is NOT an oncogenic virus? A. HTLV-1 B. Hepatitis B virus C. Varicellovirus D. Human papillomavirus
C. Varicellovirus = chickenpox virus - skin disease that is acquired in the childhood - gain access to skin via blood
All of the following are prion diseases EXCEPT __________. A. Gerstmann-Straussler-Scheinker syndrome B. kuru C. Wiles-Davidoff syndrome fatal familial insomnia D. Creutzfeldt-Jakob disease
C. Wiles-Davidoff syndrome fatal familial insomnia
Which of these statements is NOT true? A. Enveloped viruses are released from the cell by budding. B. Penetration of enveloped viruses can occur by a process called fusion. C. Uncoating can occur because of host cell lysosome action. D. Attachment of animal viruses to host cells is random and nonspecific. E. Animal viral DNA that is integrated into the host chromosome is called a provirus.
D. Attachment of animal viruses to host cells is random and nonspecific. - The specific attachment site on the host cell's surface and the availability of host cellular factors determines host range.
Which of these factors is NOT used in classifying viruses? A. Genome B. Morphology C. Host range D. Disease symptoms
D. Disease symptoms - New, fast DNA sequencing allows the International Committee on Taxonomy of Viruses to group viruses into families based on genomics and structure.
Which of the following is NOT used as a criterion to classify viruses? A. morphology B. size C. nucleic acid D. biochemical tests E. number of capsomeres
D. biochemical tests
Which of the following terms are NOT correctly matched? A. Herpesviridae; infectious mononucleosis B. Picornaviridae; polio C. Flaviviridae; hepatitis D. Picornaviridae; common cold E. Poxviridae; chickenpox
E. Poxviridae; chickenpox - Poxviridae are the causative agent of smallpox and cowpox - Varicellovirus is causative agent for chicken pox
Which of the following statements about viruses is FALSE? A. Viruses contain DNA or RNA but never both. B. Viruses have genes. C. Viruses use the anabolic machinery of the cell. D. Viruses contain a protein coat. E. Viruses use their own catabolic enzymes.
E. Viruses use their own catabolic enzymes.
Which type of microscope is needed to view a virus in the laboratory?
Electron
Discuss the arguments for and against the classification of viruses as living organisms.
For: 1) they contain either DNA OR RNA and/or a protein coat. The DNA/RNA are components of all living organisms and since virus having a component present in the living organisms can be called as a living thing. Against: 1) On the other hand, virus are "living" only when present in another living organisms or the hosts. They are inert outside of the host cell and depend on the host to be considered "alive" and multiply. When they are present free in the environment they can only be considered as particulate matter which can be "crystallized and preserved". 2) There are some virus only with protein coat and no DNA\RNA. 3) Viruses do not possess all the processes of life. They do not have the intracellular structures for metabolism. They do not respond to the environment. And, they cannot reproduce or grow on their own.
Which of the following is the preferred method for cultivating many animal viruses?
Growing them in animal cell cultures - homogenous collection of cells and can be propagated and handled like bacterial cultures = more convenient to work with than whole animals or embryonated eggs
A double-stranded, enveloped DNA virus that contains reverse transcriptase belongs to which family?
Hepadnaviridae - cause hepatitis and contain DNA - differ from other DNA viruses because they synthesize DNA by copying RNA, using viral reverse transcriptase. This DNA is the template for viral mRNA and the virus's DNA genome.
Which two virus families make DNA from an RNA template?
Hepadnaviridae and Retroviridae - use viral RNA as a template to produce complementary double stranded DNA
Identify the viral family that infects skin, mucosa, and nerve cells; causes infections that can recur because of latency, and has polyhedral geometry.
Herpesviridae
Describe the four morphological classes of viruses, then diagram and give an example of each.
Polyhedral (Adenovirus); helical (Tobacco mosaic virus); enveloped (Influenza virus); complex (Bacteriophage T4).
What is the name given to the viral DNA incorporated into a lysogenic cell?
Prophage
Viruses possess genetic material comprised of DNA or __________.
RNA - NEVER both - nucleic acid of a virus can be single or double stranded
Which enzyme is necessary for the replication of a + strand RNA virus?
RNA-dependent RNA polymerase - multiplication of RNA viruses occurs in cytoplasm of the host cell - this enzyme synthesizes a double stranded RNA
Viruses that use RNA as a template for transcribing DNA include __________.
Retroviridae - carry reverse transcriptase, which uses the viral RNA as a template to produce complementary double-stranded DNA - also degrades the original viral RNA
In some viruses, capsomeres function as enzymes as well as structural supports. Of what advantage is this to the virus?
Some bacteriophages may have issues with the cell walls, so the capsomeres act ENZYMATICALLY to cut through the cell wall and make it easier for the virus to enter the host cell.
Why may you be asked whether you are allergic to eggs before receiving a vaccination?
Some viruses are grown and isolated in embryonated eggs; especially those used for vaccines. The egg proteins may still be present in the viral vaccine preparations.
How might a virus pick up a human oncogene?
Specialized transduction - transfer specific genes - generalized transduction = any genes transferred
Consider a virus whose genome is composed of minus (-) sense RNA (for example, the rabies virus). What would be the first step in the biosynthesis of this virus?
Synthesize mRNA from the - sense RNA genome - rabies virus contains a single - strand of RNA and RNA dependent RNA polymerase that uses the - strand as a template to produce a + strand - + strand = mRNA and template for synthesis of new viral RNA
A 40-year-old man who was seropositive for HIV experienced abdominal pain, fatigue, and low-grade fever (38°C) for 2 weeks. A chest X-ray examination revealed lung infiltrates. Gram and acid-fast stains were negative. A viral culture revealed the cause of his symptoms: a large, enveloped polyhedral virus with double-stranded DNA. What is the disease? Which virus causes it? Why was a viral culture done after the Gram and acid-fast stain results were obtained?
The disease CMV disease, caused by cytomegalovirus. Since the Gram and acid-fast stain results were negative, a virus was suspected.
How would you know that viruses were multiplying in a confluent lawn of E. coli on a solid culture medium?
There would be small zones of clearing in the bacterial culture. - each virus infects a bacterium, multiplies and releases new viruses - newly produced viruses infect other bacteria in the immediate vicinity and more new viruses are produced - all bacteria in the area surrounding the original virus are destroyed = produce clearings/plaques on surface of agar
Why was the discovery of simian AIDS and feline AIDS important?
These animals are ideal for testing the pathogenicity of drug-induced mutant forms of SIV and FIV. For these purposes it will be necessary to create self-sustaining specific pathogen-free macaque and cat breeding colonies and provide increased housing facilities for infected animals. The future of AIDS research is crucially dependent on the long term availability of these animal models.
After the attachment and entry of a virus into a host cell, what is the next step in the multiplication of animal viruses?
Uncoating - viral DNA released into nucleus of host cell
What type of infectious agent causes potato spindle tuber disease?
Viroid: short pieces of naked RNA, only 300 to 400 nucleotides long, with no protein coat -nucleotide are often internally paired, so the molecule has a closed, folded, three-dimensional structure that presumably helps protect it from attack by cellular enzymes. - pathogens only of plants.
Why do we classify viruses as obligatory intracellular parasites?
Viruses absolutely require living host cells to multiply.
How do all viruses differ from bacteria?
Viruses are not composed of cells.
Which of the following would be the first step in the biosynthesis of a virus with reverse transcriptase? a. A complementary strand of RNA must be synthesized. b. Double-stranded RNA must be synthesized. c. A complementary strand of DNA must be synthesized from an RNA template. d. A complementary strand of DNA must be synthesized from a DNA template. e. none of the above
a. A complementary strand of RNA must be synthesized.
Recall from Chapter 1 that Koch's postulates are used to determine the etiology of a disease. Why is it difficult to determine the etiology of a. viral infection, such as influenza? b. cancer?
a. Viruses cannot easily be observed in host tissues. Viruses cannot easily be cultured in order to be inoculated into a new host. Additionally, viruses are specific for their hosts and cells, making it difficult to substitute a laboratory animal for the third step of Koch's postulates. b. Some viruses can infect cells without inducing cancer. Cancer may not develop until long after infection. Cancers do not seem to be contagious.
Plant viruses can't penetrate intact plant cells because (a) ___________; therefore, they enter cells by (b) ___________. Plant viruses can be cultured in (c) ___________.
a. of the rigid cell walls b. vectors such as sap-sucking insects c. plant protoplasts and insect cell cultures
Persistent viral infections such as (a) ___________ might be caused by (b) ___________ that are (c) ___________.
a. subacute sclerosing panencephalitis b. common viruses c. One example of a possible mechanism is latent, in an abnormal tissue.
Prions cause disease by __________.
altering normal proteins - nerve tissue is damaged - Prion diseases are caused by the conversion of a normal host glycoprotein called PrPC (for cellular prion protein) into an infectious form called PrPSc (for scrapie protein).
glycoprotein spikes
attachment sites on envelope of many animal viruses bind to host cell receptors = proteins having normal function hijacked by viruses - used for identification
The molecule serving as mRNA can be incorporated in the newly synthesized virus capsids of all of the following except a. + strand RNA picornaviruses. b. + strand RNA togaviruses. c. - strand RNA rhabdoviruses. d. double-stranded RNA reoviruses. e. Rotavirus.
b. + strand RNA togaviruses.
An example of lysogeny in animals could be a. slow viral infections. b. latent viral infections. c. T-even bacteriophages. d. infections resulting in cell death. e. none of the above
b. latent viral infections. - virus remain in host cell for long periods of time without producing an infection - may insert nucleic acid into host chromosome (provirus) or nucleic acid remains in repressed state in cytoplasm ex: HHV, chickenpox, oncovirus
A virus with RNA-dependent RNA polymerase a. synthesizes DNA from an RNA template. b. synthesizes double-stranded RNA from an RNA template. c. synthesizes double-stranded RNA from a DNA template. d. transcribes mRNA from DNA. e. none of the above
b. synthesizes double-stranded RNA from an RNA template.
neuraminidase inhibitor
binds to neuraminidase and blocks its actibity and prevents new virus to be released = stops spread of infection - neuraminidase = glycoprotein on surface of influenza virus that catalyze the cleavage of sialic acid
Which of the following statements is false? a. Viruses contain DNA or RNA. b. The nucleic acid of a virus is surrounded by a protein coat. c. Viruses multiply inside living cells using viral mRNA, tRNA, and ribosomes. d. Viruses cause the synthesis of specialized infectious elements. e. Viruses multiply inside living cells.
c. Viruses multiply inside living cells using viral mRNA, tRNA, and ribosomes.
A viral species is not defined on the basis of the disease symptoms it causes. The best example of this is a. polio. b. rabies. c. hepatitis. d. chickenpox and shingles. e. measles.
c. hepatitis.
The protein coat of a virus is called the __________.
capsid - protects the nucleic acid of a virus - structure determined by the viral nucleic acid and accounts for most of the mass of a virus
Members of the Adenoviridae cause __________.
common cold
Cell lines derived from transformed (cancerous) cells are called __________.
continuous cell lines - can be maintained through indefinite number of generations = immortal cell lines1
Place the following in the order in which they are found in a host cell: (1) capsid proteins; (2) infective phage particles; (3) phage nucleic acid. a. 1, 2, 3 b. 3, 2, 1 c. 2, 1, 3 d. 3, 1, 2 e. 1, 3, 2
d. 3, 1, 2
Which of the following does not initiate DNA synthesis? a. a double-stranded DNA virus (Poxviridae) b. a DNA virus with reverse transcriptase (Hepadnaviridae) c. an RNA virus with reverse transcriptase (Retroviridae) d. a single-stranded RNA virus (Togaviridae) e. none of the above
d. a single-stranded RNA virus (Togaviridae)
host range
determined by specific host attachment sites and cellular factors req for multiplication = spectrum of host cells the virus can infect - infect specific types of cells of only host species - usually narrow host range bc of surface of virus interact with receptor sites = strong association bt virus and host - bacteriophage - receptor site on cell wall of host, fimbriae or flagella - animal virus = receptor site on PM of host cell - phage therapy = use bacteriophages to treat bacterial infections (ABx resist bact)
how do antiviral medications work?
disrupt multiplication cycle by inhibiting a stage: 1) attachment: antibodies or natural ligand bind to host cell receptor and inactivate it before it meets the cell 2) uncoating: blocks proteins on capsid needed for uncoating 3) nucleic acid synthesis: prevent elongation 4) release: neuraminidase inhibitors
Place the following in the most likely order for biosynthesis of a bacteriophage: (1) phage lysozyme; (2) mRNA; (3) DNA; (4) viral proteins; (5) DNA polymerase. a. 5, 4, 3, 2, 1 b. 1, 2, 3, 4, 5 c. 5, 3, 4, 2, 1 d. 3, 5, 2, 4, 1 e. 2, 5, 3, 4, 1
e. 2, 5, 3, 4, 1
The ability of a virus to infect an organism is regulated by a. the host species. b. the type of cells. c. the availability of an attachment site. d. cell factors necessary for viral replication. e. all of the above
e. all of the above
Some viruses have a membrane-like structure on their surface, composed of lipids, proteins, and carbohydrates. This is called a(n) __________.
envelope - Some animal viruses are released from the host cell by an extrusion process that coats the virus with a layer of the host cell's plasma membrane; that layer becomes the viral envelope. - envelope contains proteins determined by the viral nucleic acid and materials derived from normal host cell components - envelopes may or may not be covered by spikes, which are carbohydrate-protein complexes that project from the surface of the envelope.
retroviridae
genus lentivirus = HIV -> AIDS - enveloped bacteria that's released by budding = sometimes the host cell survives
Shingles is a medical condition that usually occurs years after chickenpox, even though no illness is present in the intervening period of time. This occurs because human herpes virus-3 (HHV-3) is capable of __________.
latent infection - shingles occurs after chickenpox even though no illness is present in the intervening period of time - due to human herpes virus-3 (HHV-3) being a latent infection
helical virus
long rods that are rigid and flexible - most viruses - helical nucleic acid within hollow cylindrical capsid - naked = tobacco mosaic virus - enveloped = influenza measles, Ebola and rabies
During __________, the phage remains latent.
lysogeny
Influenza viruses are classified according to their hemagglutin and __________ proteins.
neuraminidase
bacteria
no intracellular parasite - has PM and binary fission - doesn't pass through bacteriological filters - has both DNA and RNA - has ATP generating metabolism and ribosomes - sensitive to ABx and not sensitive to interferon - prokaryotic cells with size 3000-1000 nm
complex virus
not symmetrical, complicated structure with polyhedra head and helical tail - enveloped animal virus = smallpox virus, HIV - T4 bacteriophage
The morphological types of viruses are ultimately determined by the
nucleic acids
virus
obligate intracellular parasite = needs living host cells - has DNA or RNA - no plasma membrane nor binary fission - can pass through bacteriological filters - no enzymes for protein synthesis nor ATP generating metabolism - no ribosomes and not sensitive to ABx but sensitive to interferon - have protein coat that surrounds nucleic acid = capsid made of capsomeres - cause synthesis of specialized structures that transfer viral nucleic acid to other cells - need to use electron microscope bc size 20-1000 nm
What is the second step of bacteriophage replication?
penetration - bacteriophage's tail releases an enzyme, phage lysozyme which breaks down portion of bacterial cell wall - tail sheath of phage contracts and tail core is driven through the cell wall - when tip of core reaches the PM the DNA from bacteriophage's head passes through core, through the PM and enters the bacterial cell
During the bacteriophage lysogenic cycle, __________.
phage DNA is inserted into the host chromosome - some viruses don't cause lysis and death of host cell when they multiply - lysogenic phages = temperate phages = proceed through lytic cycle and also capable of incorporating their DNA into the host cell's DNA to begin lysogenic cycle - lysogeny = page remains latent (inactive) and bacterial host cells = lysogenic cells
The toxin production by Corynebacterium diphtheriae carrying a temperate phage is an example of __________.
phage conversion - host cell may exhibit new properties ex: Corynebacterium diphtheriae (cause diphtheria) can produce toxin onl when it carries a lysogenic phage bc the prophage carries the gene coding for the toxin
The potential use of viruses that infect bacteria to treat bacterial infections in humans is known as __________.
phage therapy - has narrow host range and ability to kill their host cells
Infectious agents known as __________ cause Creutzfeldt-Jakob disease (CJD).
prions = proteinaceous infectious particle - nine animal disease caused by this protein = neurological diseases = spongiformencephalopathies because large vacuoles develop in the brain - human disease = kuru, CJD, Gerstmann-Straussler-Scheinker syndrome, fatal familial insomnia
Retroviridae use an RNA-dependent DNA polymerase called __________ to transcribe DNA from an RNA strand.
reverse transcriptase - use viral RNA as template to produce complementary double stranded DNA - degrades the original viral RNA - viral DNA then integrated into host cell chromosome as provirus
A virus may contain any of any of the following EXCEPT (a) _________
ribosomes - virus contains, spike proteins, ssRNA, lipid envelope, and capsid proteins - Viral enzymes are almost entirely concerned with replicating or processing viral nucleic acid. Enzymes needed for protein synthesis, ribosomes, tRNA, and energy production are supplied by the host cell and are used for synthesizing viral proteins, including viral enzymes.
In polio virus replication, the function of the antisense (- strand) RNA is to __________.
serve as a template for the production of sense (+ strand) RNA - poliovirus is a single stranded RNA virus - RNA within the virion is called a sense strand (+strand) bc it can act as mRNA - after attachment, penetration and uncoating are completed, the single stranded viral RNA is translated into two principal proteins: 1) inhibits host cell's synthesis of RNA 2) RNA dependent RNA polymerase = copies virus sense strand and makes antisense strand (- strand = template to produce more + strands)
An example of a latent virus infection is __________.
shingles - The chickenpox virus (Varicellovirus) can also exist in a latent state. - The virus gains access to the skin via the blood -> may enter nerves, where they remain latent. - Later, changes in the immune (T cell) response can activate these latent viruses, causing shingles (zoster). - The shingles rash appears on the skin along the nerve in which the virus was latent.
enveloped virus
spherical, enveloped helical or polyhedral virus - inactivated in dry, hot, and acidic environments - covers capsid = combo of lipids, proteins and carbs - covered by spikes = makes viruses attach to host cells - used for identification ex: influenza and HHV
mode of transmission of prions
spontaneous, inherited or transmissible by ingestion, transplant and surgical instruments
acyclovir
used to treat infection caused by herpes viruses like genital herpes, cold sores, shingles, and chicken pox - decrease severity and length of outbreak - analog of guanine ("G") modified by viral enzymes then incorporated into a growing viral DNA strand, replacing G - prevents DNA synthesis as elongation stops bc acyclovir can't attach any nucleotides
nonenveloped virus
withstand acidic, dry, hot environment - virus whose capsid not covered by an envelope - capsid protect nucleic acid from nuclease enzyme in biological fluids and promotes virus's attachment to susceptible host cells - more tolerant to ABx than enveloped bc enveloped = glycoprotein
