BIOL1008 Lecture Notes - Lecture 27: Encephalitis, Insomnia, Transmissible Spongiform Encephalopathy

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1 Jul 2018

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Viruses

Small particles infecting other organisms- nucleic acid surrounded by a protein

capsid

Obligate intracellular pathogens

Completely dependent on the host cell machinery for reproduction

Not necessarily pathogenic

Grouped according to their varying types of nucleic acid:

oDNA or RNA

oDouble stranded or single stranded

oPositive (protein) and negative (nucleic acid)-sense versions

DNA and RNA

DNA virus

oContains DNA

oReplicated using a DNA-dependent DNA polymerase

Retrovirus

oContains RNA and reverse transcriptase

oUses reverse transcriptase to convert its RNA into DNA

oIntegrates this viral DNA into the DNA of the host cell, which allows the

retrovirus to replicate

oSlower than just transforming RNA to protein, allows for more mutations-

very resistant to treatments as they evolve rapidly as they have lots of

mutations

Human Immunodeficiency Virus (HIV)

Retrovirus

Causes Acquired Immune Deficiency Syndrome (AIDs)

AIDS

Disease of young people

Fatality if untreated is 100%

Spread by bodily fluids and mother to baby

Transmission

oAfrica and Asia: mainly heterosexual

oWestern countries: mainly homosexuals and IV drug users but has overall

become a heterosexual disease

oPresence of other STDs increases the transmission of HIV as the reproductive

organs are already damaged

Dramatic economic and social impact, particularly in developing countries (as people

can no longer work and support family)

History

oHIV arose from a Simian Immunodeficiency Virus (SIV) of chimpanzees

o1981: CDC noticed an increase in use of drugs to treat uncommon infections,

persons with these infections often presented Kaposi’s syndrome, were

generally male homosexuals and were immunosuppressed

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oEndemic spreads in the US then reached Europe

o1983: virus isolated from human blood lymphocytes by Luc Montagnier

(Institut Pasteur- Paris)

o1986- name HIV given to the virus

o1 HIV known (arose from primate related viruses): HIV-1 (most common) and

HIV-2 (only in Western Africa)

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HIV virus

HIV infects cells of the immune system

bearing the CD4 molecule

oCD4+ T-cells (helper T-cells)

oMonocytes/ macrophages

oDendritic cells

2 locks for HIV entry in host cells:

oCD4 molecule

oCCR-5 receptor or CXCR4

receptor (chemokine receptors)



Immunosuppression

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Document Summary

Small particles infecting other organisms- nucleic acid surrounded by a protein capsid. Completely dependent on the host cell machinery for reproduction. Grouped according to their varying types of nucleic acid: dna or rna, double stranded or single stranded, positive (protein) and negative (nucleic acid)-sense versions. Dna virus: contains dna, replicated using a dna-dependent dna polymerase. Spread by bodily fluids and mother to baby. Transmission: africa and asia: mainly heterosexual, western countries: mainly homosexuals and iv drug users but has overall become a heterosexual disease, presence of other stds increases the transmission of hiv as the reproductive organs are already damaged. Dramatic economic and social impact, particularly in developing countries (as people can no longer work and support family) Hiv infects cells of the immune system bearing the cd4 molecule: cd4+ t-cells (helper t-cells, monocytes/ macrophages, dendritic cells. 2 locks for hiv entry in host cells: cd4 molecule, ccr-5 receptor or cxcr4 receptor (chemokine receptors)

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. 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.

crimsonsalmon160

2.)

a.) Are viruses that infect Archaea different from other bacterial viruses?

Yes, they do not have protein coats because of the extreme conditions where they live.

No, they consist of nucleic acid and protein just like other bacterial viruses.

Yes, the structure of archaeal viruses is always completely different from other bacterial viruses.

Yes, they have only DNA genomes.

b.) Of the following examples, which is not a common part of many viral life cycles?

The pox virus genome is replicated by DNA polymerase.

Adenoviruses attach to the cell and the nucleocapsid is taken up by the cell.

Pox viruses replicate in the cytoplasm of the cell.

Once an adenovirus virion is inside a cell, host RNA polymerases transcribe early genes

c.) Some viruses are associated with cancer. There are a variety of ways in which viruses may affect a cell in a way that may lead to cancer. Based on your knowledge of the life cycles of viruses and of molecular genetics, what is one way that this might happen?

Viral genetic material inserts into a host genome close to the termination sequence, far downstream of the promoter, and causes a silent mutation.

Viral genetic material inserts into a host genome in a repetitive noncoding region.

Viral genetic material inserts into a host genome, placing a promoter in a new location and turning on a gene that had previously been turned off.

Viral genetic material inserts into a host genome and causes a mutation in a promoter, turning off a gene that had previously been turned on.

d.) Which statement describes the difference between the normal neuron protein PrP^C and the pathogenic version PrP^Sc?

PrP^C is just a protein and the PrP^Sc is a protein with nucleic acid inside.

The PrP^C protein contains more beta sheets while the PrP^Sc protein contains more alpha helices.

The three-dimensional conformation is identical, but the amino acid sequence is different.

The amino acid sequence is identical, but the three-dimensional conformation is different.

BIOL1008 Lecture Notes - Lecture 27: Encephalitis, Insomnia, Transmissible Spongiform Encephalopathy

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