11:680:390 Lecture Notes - Lecture 19: Viral Disease, Baltimore Classification, Rna Virus

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19: Viruses II

I. Overview of Animal Virus Infection

A. Major tenets (capsid and DNA/RNA genome, infection and takeover of host,

assembly and release) universal

B. Classified by genomes

C. Most human viral diseases are caused by RNA viruses

D. Two key differences:

1. Entire virion enters the animal cell

2. Eukaryotic nucleus is the site of replication for many animal viruses

E. Size and Structure of Viral Genomes

1. The Baltimore scheme: DNA viruses (based on relationship of genome to

mRNA, includes seven classes)

F. Viral Replication

1. DNA Virus: ssRNA (+) virus → mRNA → make replicase, so it can

replicate the (-) RNA → serves as a template for more (+) RNA

2. RNA Virus Replication (retrovirus): Uses reverse transcriptase → build

DNA from (+) RNA (uses semi-conservative process)

II. Animal Virus Infection

A. Viral infection of animal cells

1. Bind specific host cell receptors, typically used for cell-cell contact or

immune function

2. Animal cells have cell differentiation: different tissues and organs express

different cell surface proteins (often viruses only infect certain tissues)

3. Uncoating occurs at the cytoplasm membrane or cytoplasm (virus fuses

with cytoplasm)

4. Viral DNA genom enters nucleus, most viral RNA is converted to DNA

within nucleocapsid

● Bind specific host cell receptors, typically used for cell-cell contact

or immune infection

B. Virion assembly and infection outcomes

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1. Virulent Infection/Lysis: most common; done by bacteriophages, only

occur in non-enveloped cells (Ex. Parvovirus)

2. Latent infection: viral DNA exists in host genome and virions are not

produced; host cell is unharmed unless/until virulence is triggered (Ex.

Herpes

3. Persistent infections: release of virions from host cell by budding does not

result in cell lysis (ex. Measles)

● Infected cell remains alive and continues to produce virus

4. Transformation: conversion of normal cell into tumor cell (Ex. Human

papillomavirus)

Stage

Bacteriophage

Animal Viruses

Attachment

● Cell wall

● Flagella & Pillus

● LPS (for

Gram-negative)

● Cell membrane

Penetration

● Injection

● Fusion/Endocytosis

Uncoating

● No uncoating

necessary

● Cytoplasm

Synthesis & Assembly

● Cytoplasm

● Nucleus

Chronic Infection

● Lysogeny

● Transformation

● Latent infection

● Persistent Infection

Release

● Lysis

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Document Summary

Parvovirus) produced; host cell is unharmed unless/until virulence is triggered (ex. Herpes: persistent infections: release of virions from host cell by budding does not result in cell lysis (ex. Infected cell remains alive and continues to produce virus: transformation: conversion of normal cell into tumor cell (ex. Dna viruses: class i viruses, pox, adenovirus: causes the common cold, herpes virus: causes fever blisters, venereal herpes, chickenpox, shingles, mononucleosis, cancer; able to remain latent for extended periods of time; reactive under stress or weakened immune system. Viruses with rna genomes: class iv (ssrna + virus, poliovirus. Lysis occurs, releasing new virions: coronaviruses (ex. Only part of genome encoding rna replicase is translated. Virions assembled in golgi complex: class v (ssrna - virus): influenza virus, budding virus with segmented genome (separate pieces) 3: genome consists of 8 different ssrna molecules, envelope studded with 2 glycoproteins important for attachment. Influenza viruses rarely attack cells outside the lungs.

Related Questions

QUESTION 1: The rabies virus primarily affects the nervous system. The specificity that the rabies virus has for neuronal host cells is primarily dictated by __________________________.

A. the helical shape of its viral capsid

B. the type of nucleic acid used for its viral genome (single-stranded, antisense RNA)

C. the spikes that protrude from its viral envelope

D. the segmented nature of its viral genome

QUESTION 2: Which of the following genome types has been observed in viruses? To be marked correct, you'll need to select all true statements, as there may be more than one correct answer.

A. Single-stranded RNA

B. Single-stranded DNA

C. Double-stranded RNA

D. Protein-based

QUESTION 3: Choose the correct statement about viral evolution.

A. RNA and DNA viral genomes evolve at equal rates.

B. Cellular genomes mutate at a faster rate than viral genomes due to their large size and increased chance of replicative mistakes.

C. DNA viruses mutate faster than RNA viruses because thymine is more susceptible to mutation than uracil.

D. RNA viruses mutate faster than DNA viruses due to a lack of proofreading replicative enzymes.

QUESTION 4: Your elderly patient is affected by shingles. After careful observation, you note that the virus responsible for the infection has an icosahedral capsid, is enveloped, and has double-stranded linear DNA as its genetic material. Based on this information, in which of the following viral families would you group this viral pathogen?

QUESTION 5: Which of the following is a key difference between lytic and lysogenic bacteriophage replication cycles?

A. Lysogenic bacteriophages release via host cell lysis, whereas lytic bacteriophages bud off from the host cell membrane.

B. The lytic replication cycle ends with host cell lysis and release of newly formed bacteriophage particles, whereas lysogenic replication leads to prophage formation.

C. Lytic replication requires an uncoating step, whereas in lysogenic replication, the bacteriophage's nucleic acid is directly injected into the host cell.

D. Whereas lytic replication enables the infection of several hosts, lysogenic replication only allows for infection of a single host cell.

QUESTION 6: Which of the following is an unsuitable culture method for an animal virus?

A. Direct inoculation of virus onto blood agar

B. Live animal inoculation

C. Tissue culture method

D. Injection of virus into embryonated eggs

1
Which of the following is a component of the HIV virus ?
A
DNA
B
Capsid
C
Nucleus
D
CD4 receptor
Answered
Change your responses to resubmit
2
Assigned as
Homework
2
What is the function of Reverse Transcriptase?
A
To insert the viral RNA into the host DNA.
B
To make an RNA copy of the viral RNA.
C
To make an RNA copy of the viral DNA.
D
To make a DNA copy of the viral RNA.
E
To insert the viral DNA into the host DNA.
Unanswered
Submit
3
Assigned as
Homework
3
Which of the following stages describes a HIV patient in who has a large number of severe opportunistic infections?
A
Primary HIV infection-lasts for a few weeks
B
Clinically asymptomatic stage-lasts for an average of ten years
C
Symptomatic HIV infection
D
Clinical AIDS
Unanswered
Submit
4
Assigned as
Homework
4
Which of the following individuals should be tested for HIV?
A
A newborn child
B
Alex, who studies excessively
C
Sarah, who takes birth control
D
Joe, who uses intravenous steroids
Unanswered
Submit
5
Assigned as
Homework
5
Harry engaged in risky activity that may have lead to exposure to HIV. Two and a half weeks later, he had an HIV test done and it showed a positive result. Which test most likely was done?
A
CD4 test
B
HIV antibody test
C
PCR test
D
Viral load test
Unanswered
Submit
6
Assigned as
Homework
6
How does an Integrase inhibitor work against the HIV virus?
A
It inhibits the generation of viral DNA from viral RNA.
B
It prevents the entry of HIV into the host cell.
C
It inhibits viral proteins from being inserted into new virus particles.
D
It prevents viral DNA from being inserted into host DNA.
E
It prevents the generation of new viral proteins.
Unanswered
Submit
7
Assigned as
Homework
7
How does a Protease inhibitor work to treat HIV infection?
A
It prevents the release of new viral particles.
B
It cleaves viral proteins interfering with their function.
C
It prevents the cleavage of host DNA preventing viral DNA from being inserted into host DNA.
D
It cleaves Reverse transcriptase preventing the generation of viral DNA.
E
It prevents the binding of gp120 to the CD4 protein.
Unanswered
Submit
8
Assigned as
Homework
8
Which of the following describes a combination therapy for HIV infected persons?
A
A preparation used for stimulating a viral response in the body.
B
A single drug given to HIV infected people since interactions with other medications may promote complications in treatment.
C
A drug cocktail-or-combination of antiviral drugs given to HIV infected people since they can be more effective than when given individually
D
A preparation used for stimulating an immune response in the body.
Unanswered
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9
Assigned as
Homework
9
answerable question reference
For HIV to reproduce, which of the following is most critical?
A
Infecting new subjects
B
Producing a Provirus
C
Entering the host cells
D
Taking over the function of DNA in the cell
Unanswered
Submit
10
Assigned as
Homework
10
HIV is a virus which has the following characteristic?
A
It takes of the RNA of the host cell which subsequently by way of transcription and translation makes new virus
B
It attacks the RNA of the host cell causing cellular death
C
It attacks the DNA of the host cell causing cellular death
D
It takes over the DNA of the host cell which subsequently by way of transcription and translation makes new virus

1. A mutation in the gene encoding the integrase enzyme rendersthe protein non-functional. How would the affect the HIV infectioncycle?

Formation of the provirus would bestopped.

Reverse transcription would nolonger be possible.

The gp120 glycoprotein would nolonger be able to bind to the CCR5 receptor.

Cutting and assembling the capsid would be halted.

2. If the viral gene is AUGCCCAGG and the mRNA used to make theviral protein is UACGGGUCC, then the virus is a :

Negative strand RNA virus

Double stranded DNA virus

Retrovirus

Positive strand RNA virus

3. Would treating prions with enzymes that digest nucleotides bean effective neutralization method?

No, prions lack amino acids.

Yes, prion nucleic acids would besusceptible to enzymatic digestion.

No, prions lack phosphodiesterbonds and would not be subject to digestion by these types ofenzymes.

Yes, the bonds between the amino acids would be hydrolyzed.

4. Most Americans born before 1970 have a permanent scar ontheir shoulders from the smallpox vaccine. Why don't youngerAmericans have one?

Smallpox has been eradicated by aworldwide vaccination program.

Smallpox is no longer lethal.

A safer less damaging vaccine wasdeveloped in the early 1970's.

The vaccine is no longer effective due to antigenic shift.

5. What kind of pathogen would retain its ability to causeinfections after being treated with powerful proteolytic chemicalsthat would destroy all proteinaceous material?

A viroid

6. Select all of the false statements concerning AIDS.

AIDS kills the patient.

Patients die as a result ofopportunistic infections.

AIDS shuts down the immunesystem.

HIV therapy (HAART) can clear thevirus from the bloodstream.

HIV therapy (HAART) can clear the virus from the patient'sbody.

7. Why do viruses only infect specific types of cells?

Viruses only attack epithelialcells, such as the cells lining the lungs.

If a host cell is weakened, viruseshave an easier time infecting it.

The initial choice is random butonce a cell type is chosen it becomes the preferred host.

The host cells have the correctsurface receptor that the virus can fit into.

Viruses infect the first cells they encounter.

8. Nucleotide analogs are a class of drugs that are highlyeffective against many types of viruses. They work by halting thereplication of viral genes. They are equally effective at stoppingthe spread of prion diseases.

True

False

9. An experimental chemical has been shown to selectively cleavephosphodiester bonds. How would the affect a virus?

Dissociate the envelope

Fragment the genome

Hydrolyze the protein coating

Alter the host binding site

Digest the capsid

10. HIV uses cell surface receptors to enter host cells. Whydoes switching from a CCR5 co-receptor to a CXCR4 co-receptoreventually shut down the immune system?

	Macrophages have CCR5co-receptors.
	T-helper cells have CXCR4co-receptors.
	T-helper cells are not involved incoordinating immune responses.
	Only macrophages are killed byHIV.

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11:680:390 Lecture Notes - Lecture 19: Viral Disease, Baltimore Classification, Rna Virus

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