Chapter 13 HW- Viruses
3 important results of lysogeny
*Lysogenic cells are immune to re-infection by the same phage *Phage Conversion *Specialized Transduction
The ability of a virus to infect an organism is regulated by:
*The host species *The type of cell *The availability of receptor sites *Cell factors necessary for viral replication
When the mRNA (originally dsRNA) is integrated and never is to exit the cell, it
*may remain latent *may be expressed to create new viruses *can convert host to tumor cell
What risks are associated with attenuated vaccines?
*may retain enough virulence to cause disease, especially in immunosuppressed individuals *Pregnant women should not receive live vaccines due to the risk of the modified pathogen crossing the placenta *Modified viruses may occasionally revert to wild type or mutate to a virulent form
DNA viruses and retroviruses induce tumors by
*some contain promoters that turn on oncogenes *others contain oncogenes *introduce genetic material causing tumor from provirus incorporation into the genome
Describe the difference between antigenic shift and antigenic drift?
ANTIGENIC SHIFT: MAJOR CHANGES in H and N spikes probably due to genetic recombination between different strains infecting the same cell ANTIGENIC DRIFT: MINOR CHANGES due to mutations in genes encoding H or N spikes may involve 1 amino acid allows virus to avoid mucosal IgA bodies
Describe the growth curve for bacteriophages and animal viruses.
Animal cells take longer to lyse; it takes 24 hours. Bacteriophages have faster lysing therefore a sharper growth curve; it takes 25 minutes.
XXXXX Which type of vaccine provides better immunity and *WHY? (attenuated or killed vaccines)
Attenuated
Toxoids
Bacterial toxins that have been inactivated by heat or chemicals. Stimulate antitoxins
What are spikes?
CHO-protein complexes that project from the surface of the envelope. *They're used for attachment but NOT penetration *May cause hemagglutination *Found only on enveloped viruses
Acellular vaccines
Fragmentation of whole-agent vaccines, collecting only the desired antigens to produce a new subunit vaccines.
What are Interferons?
Help prevent spread of viruses to new cells (viral hepatitis)
Differentiate b/w Latent and Persistent viral infections
Latent viral infections: Provirus generally not actively replicating, remains dormant in live host cell, viral DNA permanently part of host DNA Persistent viral infections: Virus actively replicates. Host cell remains alive, viral production for extended period via budding
What are some prion diseases?
Madcow disease and Creutzfeldt-Jakob disease
Viruses can contain DNA or RNA but
NEVER both
XXXEnvelopes have a
Phospholipid by-layer
How does a prion cause disease?
Prion diseases are caused by misfolded forms of the prion protein
Recombinant vaccines
Produced using genetic engineering techniques, where other microbes are genetically altered and made into vaccines with antigenic properties.
Retrociruses use reverse transcriptase to turn
RNA into DNA
Where does this replication occur?
RNA virus- cytoplasm DNA virus- nucleas
Conjugated vaccines
Some pathogens in vaccines are too small, so to enhance antigenic effects they are combined with polysaccharides.
How do antigenic shift and drift impact our ability to make an effective flu vaccine?
The body's immune response from vaccination declines over time, so the annual vaccine is needed for optimal protection. The flu vaccine is reviewed each year and updated to keep up with changing flu viruses
Some viruses are enclosed by envelopes, obtained as
bud through the cell
Continuous cell lines-
cancer cell lines (HeLa cells)
dsRNA
capsid RNA polymerase makes mRNA -> copies (-) strand to make mRNA in cytoplasm
Protein coat
capsid composed of capsomeres (units)
dsDNA
cellular enzymes transcribe viral DNA in nucleas
ssDNA
cellular enzymes transcribe viral DNA in nucleas
example of a Latent infection
chicken pox
Phage conversion of Vibrio cholerae =
cholera
hemagglutination (500) allows viruses to attach...
clumping together of red blood cells
Bacteriophages
complex virus that infects bacteria
What is HAART? (Highly Active Antiretroviral Therapy)
customized combo of diff classes of medications that a physician prescribes based on such factors as the patient's viral load (how much virus is in the blood), the strain of the virus, and other considerations like disease symptoms
Phage conversion of Corynebacterium diphtheriae =
diptheria
Phage conversion of S. aureus =
enterotoxin
Cell lines observe cytopathic effects in culture or detect by antibodies against
the virus or nucleic acid sequencing (RFLP or PCR)
What is phage therapy?
therapeutic use of lytic bacteriophages to treat pathogenic bacterial infections
Why are viruses said to be acellular?
they contain no cells and require other cells to reproduce
What is the purpose of giving imiquimod?
they promote interferon production
What step is unique for animal viruses and is not found in bacteriophages?
uncoating (step 3 in animal viruses)
Nucleic acid vaccines
use plasmid of "naked" DNA so that the body will make the protein antigen that's encoded in the DNA. The protein antigen is carried to the bone marrow to stimulate humoral and cellular immunity. ex: West Nile for horses
RNA (-) strand
used to make viral mRNA in cytoplasm
dsDNA Viral enzymes transcribe
viral DNA in virion (cytoplasm)
Common colds, AIDS, and the West Nile Virus are examples of
viral diseases
Lymes disease and strep throat are examples of
bacterial diseases
What are the characteristics of the "ultimate" vaccine?
-Affordable -Heat-stable -Orally administered -Multiple antigen -Single immunization at birth
Describe how bacteriophages are cultured.
-Can be grown either in suspensions of bacteria in liquid media or in bacterial cultures on solid media -On solid media they form plaques on a lawn of bacteria
How do antigenic shift and drift account for changes in influenzae from season to season?
-Flu viruses constantly change and mutate, might be slow due to antigenic drift.
Briefly describe the multiplication of DNA vs RNA viruses.
-In animal viruses, the capsid must be removed and replications occur in either the nucleus (DNA viruses) or in cytoplasm (RNA viruses) -Enveloped viruses bud out of the host cells -Viruses attach to the host by finding complementary receptor sites on the surface of the host cell -After the attachment, viruses enter a cell by pinocytosis. Enveloped viruses can enter by fusion. -Then uncoating process separates viral nucleic acid from its protein coat
What are the conditions necessary for a Flu pandemic?
-New influenza subtype with little or no human immunity -Must infect humans and cause illness -Must easily spread among humans
How do prophages and proviruses differ?
-Prophages can undergo lytic cycle and destroy the host -The provirus will permanently be a part of the human DNA
List three techniques used to identify viruses.
-Serological methods, such as Western blotting, are the most commonly used means -RFLPs (restriction fragment length polymorphisms) -PCR (polymerase chain reaction)
What is a prion?
-Smaller than smallest virus -Cause no immune response in a host
What are Nucleoside and Nucleotide Analogs? How do they work?
-They are anti-viral drugs and inhibit reverse transcriptase -can be used in therapeutic drugs -Include a range of antiviral products used to prevent viral replication in infected cells.
Describe the steps for multiplication of animal viruses.
1) Attachment 2) Penetration (endocytosis) 3) Uncoating (unique) 4) Biosynthesis 5) Maturation 6) Release (budding (envelope) or rupture)
Describe the steps for multiplication of bacteriophages.
1) Attachment 2) Penetration (lysozyme) 3) Biosynthesis (ECLIPSE PERIOD) 4) Maturation 5) Release (lysozyme)
Describe the lytic cycle of bacteriophages.
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
Describe the lysogenic cycle of bacteriophages.
1) Prophage exists in galactose-using host 2) Phage genome excises, taking with it the adjacent galactose gene from the host 3) Phage matures and cell lyses, releasing the phage that's carrying the gal gene 4) Phage infects a cell that cannot utilize galactose (lacking gal gene) 5) Along with the prophage, the bacterial gal gene becomes integrated into the new host's DNA 6) Lysogenic cell can now metabolize galactose
What are the essential features of all viruses?
1) obligatory intracellular parasites 2) filterable: can pass through bacterial filters 3) contain DNA OR RNA 4) contain a protein coat (CAPSID) 5) some may be enclosed by an envelope 6) most are tissue specific
What features are found in some, but not all viruses?
1. Matrix protein: external to the capsid protein 2. Phospholipid envelope external to matrix protein
What are integrase inhibitors and how do they work?
A class of antiretroviral drug designed to block the action of integrase, a viral enzyme that inserts the viral genome into the DNA of the host cell.
What are fusion inhibitors and how do they work?
A class of antiretroviral drugs that work on the outside of the host CD4 cell to prevent HIV from fusing with and infecting it.
What are protease inhibitors and how do they work?
A class of antiviral drugs widely used to treat HIV/AIDS and hepatitis caused by hepatitis C virus. They block the activity of the protease enzyme, which HIV uses to break up large polyproteins into the smaller pieces required for assembly of new viral particles.
What is Acyclovir? How does it function?
A type of nucleoside analog best known for treating genital herpes. It is also generally useful for most herpes virus infections
What is H5N1?
bird flu
Phage conversion of Clostridium botulinum =
botulism
Why are bird flus and swine flus important?
They are pandemic viruses, meaning they enter the human population
Describe how animal viruses are cultured.
They may be grown in living animals, in embryonated eggs, or in cell cultures
Vibrio cholerae and some other pathogenic bacteria only produce toxins and are capable of causing disease only when it is lysogenic. What does this mean?
Vibrio cholerae becomes toxic when the new gene of virus is being replicated with the host cell's DNA so that it blends in and will not be attacked
List examples of bacterial and viral diseases for which we are vaccinated.
Viral: influenza and chicken pox Bacterial: Tuberculosis, tetanus, chlorea
List the targets of anti-viral therapies
a. Prevention of entry into host cells b. Inhibitions of virus entering c. Integrase inhibitors d. Duplication of viral genome (RNA or DNA) e. mRNA transcription and processing i. Interferon f. Protein translation g. Post-translational modification of proteins so the successful targeted stages = Inhibitions of virus entering, Duplication of viral genome (RNA or DNA), mRNA transcription and processing, Post-translational modification of proteins
Phage conversion
acquire new properties (such as toxin production)
ssRNA (+) strand
acts as mRNA -> makes RNA polymerase -> synthesizes
Attenuated whole-agent vaccines
alive but significantly weakened.
N = Neuraminidase (100)
allow virus to exit the cell
ssRNA (-) strand
already contains the RNA polymerase -> viral enzyme copies viral RNA to make mRNA in cytoplasm
Differentiate between attenuated and killed (inactive) vaccines
an attenuated vaccine is purely the virus whereas the inactivated vaccine has been genetically altered
What are retroviruses?
any of a group of RNA viruses that insert a DNA copy of their genome into the host cell in order to replicate example: HIV
Describe the chemical and physical structure of both enveloped and nonenveloped viruses.
enveloped: consists of some combo of lipids, proteins, and carbs. 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. In many cases, the envelope contains proteins determined by the viral nucleic acid and materials derived from normal host cell components. Roughly spherical nonenveloped: capsids that aren't covered by an envelope. The capsid of a nonenveloped virus protects the nucleic acid from nuclease enzymes in biological fluids and promotes the virus's attachment to susceptible host cells.
Diploid cell lines-
from human embryos (widely used) maintained for approximately 100 generations
Primary cell lines-
from tissue slices, die out after a few generations.
Shape of viruses
helical or polyhedral (icosahedron) - 20 faces w/ 12 corners
Inactivated whole-agent vaccines
inactivated with heat, formulin, or other chemicals.
Example of a virus with envelope + spikes
influenza
dsRNA- once (-) strand is made as mRNA in cytoplasm,
it integrates as provirus and never exits
Viruses must grow in
living cells
Bacteriophages are lytic, meaning they cause
lysis and cell death
example of a Persistent viral infection
measles and HIV-1
Bacteriophages grow as a one step curve
no new infective virus in culture until after biosynthesis and maturation, leads to burst (released by lysis)
Define oncogene and transformed cell.
oncogene: a gene that in certain circumstances can transform a cell into a tumor cell transformed cell: Has increased growth, loss of contact inhibition
Specialized transduction
phage packages some bacterial DNA with its own viral DNA
Some bacteriophages are lysogenic, meaning the
prophage incorporates into host DNA
Lysogeny is comparable to latent infections
provirus never leaves the host genome
burst
released by lysis
Phage conversion of Streptococcus pyogenes =
scarlet fever
Why are viruses host, receptor and cell specific?
specificity is due to the precise affinity of viral surface proteins or glycoproteins for complementary proteins or glycoproteins on the surface of the host
How are spikes used to help viruses cause infections?
spikes help the virus attach to the surface of the host cell
Eclipse period
the time between infection by (or induction of) a bacteriophage, or other virus, and the appearance of mature virus within the cell; an interval of time during which viral infectivity cannot be recovered
Discuss the relationship between DNA- and RNA-containing viruses and cancer.
~10-15% of cancers are caused by viruses -Several DNA viruses are retroviruses and oncogenic, active oncogenes transform normal cells into cancerous cells -The genetic material of oncogenic viruses become integrated into the host cell's DNA. *Among the RNA viruses only retroviruses seem oncogenic