BIOLOGY 3 Lecture Notes - Lecture 29: Peptidoglycan, Prophage, Oncogene

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6 Dec 2020

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Viruses gain entry into and are specific to a particular host cell because portionsof the capsid (or spikes of the envelope) adhere to specific receptor sites on host cell surface. Viral nucleic acid then enters a cell, where the viral genome codes for production of protein units in the capsid. Bacteriophages (phages) are viruses that parasitize a bacterial cell lytic cycle: a bacteriophage life cycle of five stages where a virus takes over operation of the bacterium immediately upon entering it and then destroys the bacterium. Attachment: portions of the capsid bind with receptors on the bacterial cell wall. Penetration: a viral enzyme digests part of cell wall; the viral dna is injected into a bacterial cell. Biosynthesis: synthesis of viral components - begins after the virus brings about inactivation of host genes not necessary to viral replication. Maturation: viral dna and capsids are assembled to produce several hundred viral particles and lysozyme, coded by the virus, is produced.

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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.

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BIOLOGY 3 Lecture Notes - Lecture 29: Peptidoglycan, Prophage, Oncogene

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