Micro - Virology (Viral Basics) & Prions

Question 1

Name, draw, and label the 3 progressions of general features for viral structure.

Answer 1

(1) Naked virus with icosahedral capsid - nucleic acid, capsid (2) Envelope virus with icosahedral capsid - nucleic acid, capsid, lipid bilayer, surface protein (3) Enveloped virus with helical capsid - helical capsule with nucleic acid inside, lipid bilary, surface protein; See p. 153 in First Aid for drawing and labels

Question 2

What are 4 processes in viral genetics?

Answer 2

(1) Recombination (2) Reassortment (3) Complementation (4) Phenotypic mixing

Question 3

What is recombination?

Answer 3

Exchange of gene between 2 chromosomes by crossing over within regions of significant base sequence homology

Question 4

What is reassortment? What virus and consequences should you associate with this process?

Answer 4

When viruses with segmented genomes (e.g., influenza virus) exchange segments; High-frequency recombination. Cause of worldwide influenza pandemics

Question 5

What is complementation?

Answer 5

When 1 or 2 viruses that infect the cell has a mutation that results in a nonfunctional protein. The nonmutated virus “complements” the mutated one by making a functional protein that serves both viruses

Question 6

What is phenotypic mixing?

Answer 6

Occurs with simultaneous infection of a cell with 2 viruses. Genome of virus A can be partially or completely coated (forming pseudovirion) with surface proteins of virus B. Type B protein coat determines the tropism (infectivity) of the hybrid virus. However, the progeny from this infection have a type A coat that is encoded by its type A genetic material.

Question 7

What are the different kinds of viral vaccines?

Answer 7

(1) Live attenuated (2) Killed (3) Recombinant

Question 8

What kind of immunity do live attenuated vaccines induce? What is a potential side effect?

Answer 8

Induce humoral and cell-mediated immunity, but have reverted to virulence on rare occasions

Question 9

Contrast live attenuated and killed/inactivated vaccines in terms of immunity induced and risks posed.

Answer 9

LIVE ATTENUATED - Induce humoral and cell-mediated immunity, but have reverted to virulence on rare occasions; KILLED/INACTIVATED - Induce only humoral immunity but are stable

Question 10

What are examples of live attenuated vaccines?

Answer 10

(1) Smallpox (2) Yellow fever (3) Chickenpox (VZV) (4) Sabin’s polio virus (5) MMR (6) Influenza (intransal); LIVE attenuated - SMALLpox, YELLOW fever, CHICKENpox (vzv), SABIN’S polio virus, MMR, Influenza (IntraNasal) = Think: “LIVE! one night only! see SMALL YELLOW CHICKENS get vaccinated with SABIN’s and MMR! It’s INcredible!”

Question 11

What are examples of killed vaccines?

Answer 11

(1) Rabies (2) Influenza (injected) (3) Salk Polio (4) HAV vaccines; Think: “RIP Always, salK = Killer”

Question 12

What are examples of recombinant vaccines? Give specifics on antigens/types as they apply.

Answer 12

(1) HBV (antigen = recombinant HBsAg) (2) HPV (types 6, 11, 16, and 18)

Question 13

What is a live attenuated vaccine that can be given to HIV-positive patients, and in what context?

Answer 13

MMR = measles, mumps, rubella (live attenuated vaccine that can be given to HIV-positive patients) who do not show signs of immunodeficiency)

Question 14

What are 2 advantages of live attenuated vaccines? In what patient population(s) is it dangerous to give live vaccines?

Answer 14

(1) No booster needed for live attenuated vaccines (2) Cellular and humoral immunity (unlike only humoral in Killed vaccines); Immunocompromised patients & their close contacts

Question 15

What kind of nucleic acid material do nearly all DNA viruses have? What is the exception, and what is its nucleic acid material?

Answer 15

dsDNA, except Parvoviridae = ssDNA; Think: “Parvus = small” and “all are dsDNA (like our cells), except ‘part-of-a-virus’ (parvovirus is ssDNA”

Question 16

What is the shape/form of nucleic acid material in nearly all nearly DNA viruses? What are the exceptions, and what is their shape/form of nucleic acid material?

Answer 16

Linear, except papilloma-, polyoma-, and hepadnaviruses = circular

Question 17

What kind of nucleic acid material do nearly all RNA viruses have? What is the exception, and what is its nucleic acid material?

Answer 17

ssRNA, except Revoiridae = dsRNA; all are ssRna (like our rna), except (REOvirus) = dsRNA; Think: “REpeatO-virus”

Question 18

What are the positive-stranded RNA viruses?

Answer 18

(1) Retrovirus (2) Togavirus (3) Flavivirus (4) Coronavirus (5) Hepevirus (6) Calcivirus (7) Picornavirus; Think: “i went to a RETRO TOGA party where i drank FLAVored CORONA and ate HIPPY CALIfornia PICkles.”

Question 19

Which purified nucleic acids are infectious?

Answer 19

INFECTIOUS: Purified nucleic acids of most dsDNA (except poxviruses and HBV) and (+) strand ssRNA (like mRNA) viruses

Question 20

Which naked nucleic acids are not infectious, and why?

Answer 20

NON-INFECTIOUS: Naked nucleic acids of (-) strand ssRNA and dsRNA viruses, because they require polymerases contained in complete virion

Question 21

Where do nearly all DNA viruses replicate? What is the exception?

Answer 21

All replicate in the nucleus (except poxvirus)

Question 22

Where do nearly all RNA viruses replicate? What are the exceptions?

Answer 22

All replicate in the cytoplasm (except influenza virus and retroviruses)

Question 23

What are naked viruses? What are examples of naked viruses?

Answer 23

Nonenveloped viruses; (1) Papillomavirus (2) Adenovirus (3) Picornavirus (4) Polyomavirus (5) Calcivirus (6) Parvovirus (7) Reovirus (8) Hepevirus; Think: “give PAPP smears and CPR to a NAKED HEPpy (hippy), DNA = PAPP, RNA = CPR, & hepevirus”

Question 24

How do enveloped viruses generally acquire their envelopes? What is the exception to this, and how does it acquire its envelope?

Answer 24

Generally, enveloped viruses acquire their envelopes from plasma membrane when they exit from cell; Exceptions include herpesviruses, which acquire envelops from nuclear membrane

Question 25

What are the 5 general rules of DNA viruses, and their exceptions?

Answer 25

(1) are HHAPPPy viruses (Hepadna, Herpes, Adeno, Pox, Parvo, Papilloma, Polyoma) (2) are double stranded (except Parvo = single stranded) (3) are linear (except Papilloma & Polyoma = circular, supercoiled & Hepadna = circular, incomplete) (4) are icosahedral (except pox = complex) (5) replicate in the nucleus (except pox = carries own DNA-dependent RNA polymerase)

Question 26

What are the DNA viruses?

Answer 26

Hepadna, Herpes, Adeno, Pox, Parvo, Papilloma, Polyoma; Think: “DNA viruses are HHAPPPy viruses”

Question 27

Are nearly all DNA viruses double stranded or single stranded? What is the exception to this general rule?

Answer 27

Double stranded; Except Parvo = single stranded

Question 28

What shape/form is the nucleic material in nearly all DNA viruses? What are the exceptions to this general rule?

Answer 28

Linear; Except Papilloma & Polyoma (circular, supercoiled) & Hepadna (circular, incomplete)

Question 29

What shape of caspid do nearly all DNA viruses have? What is the exception?

Answer 29

Icosahedral; Except pox = complex

Question 30

Where do nearly all DNA viruses replicate? What is the exception?

Answer 30

Replicate in the nucleus; Except pox (carries own DNA-dependent RNA polymerase)

Question 31

What causes prion diseases?

Answer 31

Prion diseases are caused by the conversion of a normal cellular protein termed prion protein (PrP^c) to a Beta-pleated form (PrP^sc), which is transmissible

Question 32

Again, what causes prion disease? Is it transmissible?

Answer 32

Prion diseases are caused by the conversion of a normal cellular protein termed prion protein (PrP^c) to a Beta-pleated form (PrP^sc), which is transmissible

Question 33

What role does PrP^sc directly play in prion disease?

Answer 33

PrP^SC resists degradation and facilitates the conversion of still more PrP^c to PrP^sc

Question 34

What conditions result from the accumulation of PrP^sc?

Answer 34

Accumulation of PrP^sc results in spongiform encephalopathy and dementia, ataxia, and death

Question 35

What are the different forms of prion disease? Give an example of each form.

Answer 35

It can be (1) Sporadic (Creutzfeldt-Jakob disease – rapidly progressive dementia), (2) Inherited (Gerstmann-Straussler-Scheinker syndrome), or (3) Acquired (kuru)