Chapter 13 Virusis, Viroids, & Prions Flashcards
What causative agent did Iwansky find and what did he say about them?
Found the causative agent of Tobacco mosaic disease (TMD) ad they were very small because they passed through filters.
What is another word for Virus and when what he fairest human disease associated with a virus?
Poison
Yellow fever
What is a bacteriophage or phases?
Viruses that infect bacteria
What are the general characteristic of Viruses? Where do they live and thrive?
What genetic material do they contain?
Obligatory Intracellular parasites
Contain DNA or RNA never both. They are not complete organisms and lack enzymes and protein machinery
How are viruses enclosed?
Contain a protein coat (capsid)
Some are enclosed by an envelope
Some viruses have spikes
What cells do viruses infect? Do they infect all?
How is the host range determined?
Most viruses infect only specific types of cells in one host
Host range is determined by specific host attachment sites (receptors) on cell surface
What are the differences between Virions and Virus?
Outside of the cell what is a virus called?
Viruses have extracellular and intracellular state
Outside a cell, a virus is called virion
A complete infectious particle is called a what?
Virion is complete infectious particle
Once inside of the cell what happens to a virion?
Capsid is removed and its called a virus
What the three basic shapes of viruses?
Polyhedral (many sides)
Helical
Complex
Virion structure is referred to as?
What are its contents and the ways it is covered? Give Example?
Complete infections Viral Particle
Capsid : Adenovirus poliovirus
Envelope
Spikes : Influenza virus
Define the structure of a capsid?
What are the small units that make up the capsid?
Capsomeres are the small units that make up the capsid
Polyhedral meaning many sides
What is the morphology of a Helical Virus?
What determines the shape?
What are two examples
Shape of viruses depends on Capsid
-looks like a coiled rod
Ebola virus
Rabies Virus
What is the morphology of a Complex Virus?
What is an example? What does it infect?
Example: Bacteriophage
Means bacteria eater and they infect bacterial cells
Polyhedral head that contains the nucleic material
Sheath, Tail fiber, baseplate, and Pin
What is the morphology of an Enveloped Virus?
What is it made of?
Give an example
Some have envelopes (lipids, proteins, carbohydrates)
Envelope could be from a host cell with different shapes
Could have ssDNA, ssRNA, dsRNA, dsDNA
The nucleic acid is encased in a Capsomere
Ex. Influenzavirus
What is the Taxonomy of Viruses, how are they classified?
Classified by:
Type of nucleic acid (RNA or DNA)
Envelope
Shape and size
What is a viral species?
How are subspecies designated?
Viral Species: a group of viruses sharing the same genetic information and ecological niche (host)
Common names are used for species
Subspecies are designated by a number
What is the specific epithet use for?
If there is a subspecies how is it classified?
They are not used they have descriptive common names for GE use like Lentivirius that causes AIDS
HIV (Human Immunodeficiency Virus)
Subspecies (if any) classified by a number
How do viruses grow?
Viruses must be grows in living cells because they lack the machinery to survive outside of a host
What do bacteriophages form on bacteria?
Bacteriophages form plaques on a lawn of bacteria
What is plaque?
What is a plaque assay?
A single virus is suspension
the concentrations of viral suspensions are measured by plaque forming units
A plaques assay is a method to quantify viruses
How are animal viruses grown?
Grown in:
Living animals
Embryonated eggs
Animal and plant viruses may be grown in?
Grown in cell culture which have replaced embryonated eggs
How are cell culture lines started?
By treating a slice of animal tissue with enzymes that separate the individual cells that are then suspended in a solution that provide the osmotic pressure, nutrients, and growth factors needed for growth.
Cells can form monolayers which can cause the cells to deteriorate as they multiply. This is called what?
Cytopathic effect (CPE) which are infected cell cultures
Viruses can be grown in what types of cells lines?
Primary
Diploid
Continuous cells lines
What are primary cell lines?
Derived from tissue slices, tend to die out after only a few generations
What are diploid cell lines?
Developed from human embryos that can be maintained for about 100 generations
When viruses are routinely grown in a laboratory what cell line is used?
Give an example?
Continuous cell lines- transformed (cancerous) cells that can be maintained through an indefinite number of generations (indefinitely
HeLa cells- she died in 1951 and the cells are still being used.
What is needed for the multiplication of viruses?
What are the two types of multiplication cycles?
They need a living cell and use the host metabolic machinery to survive.
Lyric
Lysogenic
Which one has the best know mechanisms for multiplication of viruses?
Bacteriophages
What is the lytic cycle?
Ends with the lysis and death of the host cell
What is the Lysogenic cycle?
Unlike the lytic cycle that ends in lysis, the lysogenic cycle the host remains alive.
Which cycle does E.coli follow?
Which cycles have been studied the most?
Follows the lytic cycle
T-even bacteriophages (T2,T4,T6) have been studied the most
What are the five steps of the Lytic Cycle?
Attachment Penetration Biosynthesis Maturation and Assembly Release
What is the attachment step of the lytic cycle?
Attachment (absorption): After a chance collision, phage attaches by tail fibers to complementary host receptors on cell wall
What is the penetration step of the lytic cycle?
After attachment, the T-even bacteriophage injects its DNA into the bacterium, this is done when the bacteriophage’s tail releases an enzyme, Phage Lysozyme, which breaks down a portion of the bacterial cell wall
The rest of the phage stays outside
What is the Biosynthesis step of the lytic cycle?
Phage takes control of the host protein machinery and stops host protein says thesis and starts making viral proteins
What is the Eclipse period?
The period during viral multiplication when complete, infective virions that are not yet presence.
The particles cannot be found for a short period of time.
What is the Maturation and Assembly state?
Phage capsid and nucleic acids are synthesized separately and are assembled into phage particle
What is the Release stage of the Lytic Cycle?
Phage lysozyme lyses the wall and phage particles are released. Newly released viruses will infect other cells on and on
What is the time between the page attachment and its release time? What is it called?
20-40 mins
Burst time
What is Burst size?
The number of phases released form each cell is called Burst Size
What is a one step growth curve?
It’s the multiplication of a virus
What are the results of multiplication of bacteriophages of the lytic cycle?
Phage causes lysis and death of host cell
What are the results of the Lysogenic cycle?
Phage does not cause lysis of the host cell
Phage DNA is incorporated into host DNA and remains latent (inactive)
Bacterial host cell of the Lysogenic cycle is now called?
The inserted phage is now called?
Lysogenic cell
Prophage
Lysogenic phases are called?
Give and example
Temperate phages
E.g. Bacteriophages Lambda
What are the three important restless of Lysogeny?
- Lysogenic cells are immune to re infection by the same phage
- Phage conversion: infection affects host cell function such as, toxin production
E.g. Toxins in Corynebacterium diphtheria and Vibrio cholerae are carried by phage
- Specialized transduction: only certain bacterial genes can be transferred
What are the differences of multiplication of Animal Viruses?
Penetration is different
Goes through unloading
Do not have appendages like a tail
What are the steps of Multiplication of Animal Viruses
Attachment: viruses attach to specific receptors
Penetration: by pinocytosis for non-envelope viruses and by fusion in enveloped viruses
E.g HIV
Uncoating: viral nucleic acid is released from capsid
Biosynthesis: Production of nucleic acid and proteins
Maturation: Nucleic acid and capsid proteins assemble
Release by budding (enveloped viruses) or lysis (rupture)
What is Papillomavirus?
What does it cause?
Double stranded DNA nonenveloped viruses
Human wart virus
-genial warts
What are Adenoviruses?
Double-stranded DNA, nonenvelped viruses
- respiratory infections in humans-common cold
- tumors in animals
What is the Human Herpesviruses (HHV)?
Double stranded DNA
Enveloped viruses
What is simplexviruses?
Causes cold sores, fever blisters and genital herpes
Double stranded DNA and enveloped
What is Varicellovirus?
Causes chickenpox
What is Lymphocryptovirus? What is another name for it and what does it cause?
HHV-4 or Epstein-Barr virus causes infectious Mononucleosis
What does (HHV-8) cause?
Kaposi’s sarcoma
How do Herpesvirus remain latent in host cells?
They prevent (programed cell death) apoptosis of B lymphocytes so infected cell becomes immortal
What Poxviruses?
Give an example and what does it cause
Double stranded DNA
Enveloped viruses
Smallpox and cowpox
Causes skin lesions filled with pus
What are the steps of Multiplication of DNA virus?
Virion attaches to the host
Virion enters the cell and the DNA is Uncoated
Potion of the viral DNA is transcribed producing mRNA that encodes early viral proteins
Viral DNA is replicated
Capsid proteins are then synthesized and the virions mature
Then release
What is the Sense strand RNA (+)
It can adt as mRNA to synthesize (translation) protein
What is the antisense strand RNA (-)
Serves as a template to produce (+) strands
What is type of virus is Picornaviruses? Give example
RNA virus
Ex poliovirus are ssRNA and the RNA is (+) strand
What is Rhabdoviruses?
Give Ex.
Rabies virus
-ssRNA and RNA is (-) strand
What are Reoviruses?
They are named for their habitat: respiratory and enteric (digestive) system
They cause respiratory and intestinal tract infection
-dsRNA
Newly produced viral protein produces RNA-dependent RNA polymerase, which creates RNA (-) strands mRNA + strand and - strand from the double strand
Why are Reoviruses referred to as orphan viruses?
What do they cause
They were not associated with an diseases at first and given the name orphan viruses
Cause Colorado Tick Fever
What are Retroviruses?
The first two letters comes from Reverse Transcriptase
Reverse Transcriptase which uses viral RNA as a template to form dsDNA (viral)
They have two copies of (+) strand RNA
What do Retroviruses cause?
Some cause cancer: Oncogenic viruses
Includes all RNA tumor viruses
Lentivirus which includes HIV
What is the viral DNA called that integrates into hose chromosomes?
The DNA is called Provirus
What is the difference between a prophage and Provirus?
The Provirus never comes out of the chromosome
What are Picornaviruses?
Such as enteroviruses and poliovirus
They are the smallest of viruses, single-stranded RNA, + strand
Nonenveloped
Hep A
What are Coronaviruses?
What do they cause?
Single stranded RNA
+ strand
Enveloped
Cause upper respiratory infections
SARS (Severe Acute Respiratory Syndrome)
What is antigenic shift in viruses?
Ex.
The virus can shift and cross over from one species to another
Influenza A. viruses are seen in many animals such as birds, pigs and horses
How are the subtypes differentiated by on viruses?
The subtypes differ in the antibody on the surface of the envelope of virus and appear as spikes
HA: hemagglutinin
NA: neuraminidase
It’s the combinations of HA and NA that creates different subtypes
What are the three subtypes of human influenza A viruses?
H1N1
H2N2
H3N2
What is antigenic shift?
Genes are mixed and new virus will emerge which is antigenic shift
What is Hepadnavirus?
-dsDNA, enveloped
Causes hepatitis B
Synthesize DNA by coping RNA using viral reverse Transcriptase
Just like Retroviruses
How are enveloped viruses produced?
What are the effects on the host cell?
Envelopes consists of protein, lipid, and carbohydrate
A process called budding
The host cell is not killed
What are the steps of Multiplication of a Retrovirus?
- RV enters by fusion between attachment spikes and host cell receptors
- Uncoating releases the viral RNA genomes and enzyme reverse Transcriptase
- Reverse Transcriptase copies viral RNA to produce dsDNA
- The new viral DNA is transported to the nucleus and integrates into its chromosome as a provirus that can be replicated
- transcription of the Provirus occurs producing viral RNA, which encodes for the capsid
- capsid forms
- mature Retroviruses leaves the host cell acquiring an envelope and attachment spikes
what are some examples of viruses causing cancer?
Chicken sarcoma: cancer of connective tissues
Adenocarcinoma: in mice (cancer of glandular epithelial tissue)
How is it proven that viruses cause cancer?
Actually the connection is hard to prove because:
Infections by virus does not always cause disease
There is a long incubation period
Cancers are not contagious as are viral infections
What are Oncogenes?
Some viruses that produce cancer carry specific cancer-causing genes called Oncogenes.
How do oncogenes cause cancer?
These genes can be inserted into host chromosome and cause cancer
What did Bishop and Varmus discover?
They made the discovery that oncogenes are altered version of a gene found in formal cells
Therefore viruses pick the gene and change it to oncogene
What is a proto-oncogene?
A normal gene with a potential to become a oncogene
What are Oncoviruses?
Viruses that can induce tumors are called oncogenic viruses or (oncoviruses
What is the not normal process that tumor cells go through and what takes place?
Tumor cells go through transformation that is not normal
These transformed cells have increased growth, loss of contact inhibition, tumor-specific transplant antigens (TSTA, and T antigens
What happens to the genetic material of oncogenic viruses?
Becomes integrated into the host cell’s DNA
Example of DNA oncogenic viruses
Papilomaviruses?
EBV?
Hep B
Papilomaviruses (warts): cause cervical cancer
EBV causes two cancers
-burkit’s lymphoma
-nasopharyngeal carcinoma
1982, a 12 received a bone marrow transplant and died due to infectious mono
Hepatitis B: causes liver cancer
Among the RNA viruses, what causes cancer?
Give an example?
Only the oncoviruses in the family Retroviridae cause cancer
Human T-cell leukemia virus (HTLV-1 and HTLV-2) cause T-cell leukemia and lymphoma in humans
What are the 5 Oncogenic DNA viruses listed?
Adenoviruses Herpesviruses Poxviruses Papilomaviruses Hepadnaviruses
Oncogenic RNA viruses include?
Retroviridae
Viral RNA is trascribed to DNA, which can integrate into host DNA
HTLV- 1 and 2
What are latent viral infections?
Give an example?
A virus can remain in equilibrium with the host and not actually produce disease for a long period of time.
They are asymptomatic
Cold sores caused by herpes simplex virus. This sits in the nerve cells a fever or sunburn, or stress can bring this on.
Chickenpox (Varicellovirus) to shingles (zoster)
What are Persistent or Chronic Viral Infections?
Give an example?
Diseases occurs gradually over a long period and are typically fatal
SSPE- Subacute sclerosis panencephalitis which is caused by measles
These build up before they appear rather than latent viral infections that appear suddenly
What are Prions?
Made of proteins only. No nucleic acids
Have a long incubation time
Where did the name Prion come from?
Prusiner coined the name prion for Proteinaceous Infectious Particle
How are Prions formed?
Inherited and transmissible by ingestion, transplant and surgical instruments
What are some Prion diseases?
What types of diseases are they?
Bovine Spongiform encephalopathies (Mad Cow Disease)
Sheep Scrapie
Kuru, CJD in humans
All of these are neurological diseases
How are Prions caused?
Disease is caused by conversion of normal host glycoproteins PrPc into an infections form called PrPsc
What is PrPc?
Normal cellular prion protein, on the cell surface
What is PrPsc?
Scrapie protein; accumulated in the brain cells, forming plaques
What is the difference between animal viruses and plant viruses with respect to plant viruses?
Plant disease are caused by viroids that are short naked pieces of RNA about 300-400 nucleotides long
No capsid or protein coat
