Topic 12: Viruses

membranous layer

Many viruses are bound by an outer, flexible, ________ called the envelope- for invasion.

Genus Ebolavirus

________- total 5 species, 4 species pathogenic to human, Reston virus affects primates only.

virus production

May be synthesized during ________ or be a part of the plasma membrane of the host cell.

Dilutions of virus preparation

________ made and plated on lawn of host cells.

Negative sense strand

________- complementary to mRNA.

Viruses

acellular infectious agents

Genus Ebolavirus

total 5 species, 4 species pathogenic to human, Reston virus affects primates only

3 months after recovery, found in semen

sexual transmission

BSL

1

BSL

2

pathogen, moderate hazard, personal protection needed, need to be immunized for Hep B, TB test, immunocompromised/immunosuppressed possibly denied, ex

Hep A, B, C, HIV, flu, MRSA

BSL

3

self-closing door, separate entrance required, registration with government required, lab coats need to be dontaminated before laundry, ex

west nile virus, anthrax, rabies virus, SARS virus

BSL

4

lift-threatening diseases, separate building, pospressure air supplied, full body suit, ex

ebola

virions lacking envelopes

naked viruses

range from

10 to 800 nm

capsid

protein coat surrounding the nucleic acid (DNA or RNA)

(+) sense ssRNA

single strand RNA → ready to infect

Rhino ss +RNA

single strand RNA → ready to infect

ex

covid

envelope

surrounds the capsid in some viruses

many viruses are bound by an outer, flexible, membranous layer called the envelope

for invasion

Nucleic acid

linear, circular or segmented

DNA

doubled stranded or single stranded (herpes, chickenpox)

RNA

double stranded or single stranded (ebola, flu, west nile)

Positive sense strand

same as mRNA, ready for translation → protein synthesis

Negative sense strand

complementary to mRNA

transcriptase

ready for translation → protein synthesis

Antigenic drift

point mutation, mostly "silent"

Antigenic shift

major genome change due to recombination, last years flu

-40 Archaeal viruses have been identified;

15 of these have been assigned to virus taxa

First to describe RNA dependent RNA polymerase

which virus

I

dsDNA viruses (e.g

II

ssDNA viruses (+ strand or "sense") DNA (e.g

III

dsRNA viruses (e.g

IV

(+)ssRNA viruses (+ strand or sense) RNA (e.g

V

(−)ssRNA viruses (− strand or antisense) RNA (e.g

VI

ssRNA-RT viruses (+ strand or sense) RNA with DNA intermediate in life-cycle (e.g

VII

dsDNA-RT viruses (e.g

Adsorption to specific receptor site

porin protein and LPS

Penetration of the cell wall

peptidoglycan degrades

Cell lysis and phage release

12 minutes after initial absorption (100-150 new phages)

in T4

E. coli system, -150 viral particles are released

Iatrogenic

prion-contaminated human growth hormone, dura mattaer graft

New variant

infection from Bovine prions

Familial

Germ-line mutation in the PrP gene

Sporadic

Somatic mutation or spontaneous conversion into disease form

Viruses are ___ infectious agents.

acellular

How many biosafety levels are there?

4

What is BSL-1?

minimal potential threat, no pathogen, standard open lab benches without the use of special equipment

What is BSL-2?

pathogen, moderate hazard, personal protection needed, need to be immunized for Hep B, TB test, immunocompromised/immunosuppressed possibly denied

What is BSL-3?

self-closing door, separate entrace required, registration with government required, lab coats need to be decontaminated before laundry

What is BSL-4?

life-threatening diseases, separate building, pos-pressure air supplied, full body suit

What biosafety level is micro lab?

1

What does enzootic mean?

endemic within

What does epizootic mean?

epidemic among animal

Who developed porcelain bacterial filters used later in discovery of viruses?

charles chamberland

Who demonstrated that causative agent of tobacco mosaic disease passed through bacterial filters and thought agent was toxin?

dimitri ivanowski

Who showed that causative agent of tobacco mosaic disease was still infectious after filtration and referred to agent as filterable virus?

martinus beijerinck

Who discovered in 1935 that viruses were made of nucleic acid and protein?

wendell stanley

What are characterisitics of viruses?

exceptionally small; contain a single type of nucleic acid (either DNA or RNA); possesses a protein coat surrounding the nucleic acid; multiply inside living cells using the metabolic machinery of the cell

What is a virus that has a protein coat but also an envelope outside of the protein coat?

virion

Since viruses have no metabolic machinery of their own, they are ___.

obligate parasites

Can viruses respond to stimuli?

no

Can viruses evolve?

yes

Are viruses sensitive to antibiotics?

no

Are viruses sensitive to interferon?

yes

Do viruses have a plasma membrane?

no

Can viruses pass through bacteriological filters?

yes

Viruses cannot reproduce ___ of living cells nor carry out cell division like prokaryotes and eukaryotes.

independently

What is the size range of viruses?

about 10-800 nm in diameter

Most viruses are too small to be seen with a ___ microscope.

light

All ___ contain a nucleocapsid.

virions

What are nucleocapsids composed of?

nucleic acid (DNA or RNA) and a protein coat (capsid)

Virions with envelopes are called ___.

enveloped viruses

Virions without envelopes are called ___.

naked viruses

A naked virus only has ___ and ___.

nucleic acid and capsid

A enveloped virus has ___ (4).

nucleic acid, capsid, envelope, and spike

A capsid (protein coat) is composed of protein subunits called ___.

capsomeres

Capsomeres can be arranged in several ___, which gives a virus its morphology.

configurations

What are the four major morphological groups of viruses?

helical, polyhedral, enveloped, and complex

What are helical viruses?

tobacco mosaic virus; + sense ssRNA; resemble long rods and may be flexible or rigid; the capsid is helical surrounding the nucleic acid

What are polyhedral viruses?

adeno dsDNA; rhino ss+RNA; +sense ssRNA; a many-sided virus particle; capsid is usually in the shape of an iconsahedron (min 12 triangular faces and corners)

What are envelopes?

surrounds the capsid in some viruses; may be synthesized during virus production or be a part of the plasma membrane of the host cell

What is an evelope composed of?

lipids, proteins, and carbohydrates

Coronavirus is a ___ viruses.

enveloped

Complex viruses may be the target of ___.

new antibiotics

What are complex viruses?

have variation of icosahedral shape in phage; do not fit into the category of having helical or icosahedral capsids

It was first thought that all virions lacked ___.

enzymes

It is now know that a variety of virions have enzymes, mostly within the ___.

capsid

In eukaryotic viruses some envelope are proteins, which are viral encoded, and may project from the envelope surface as ___.

spikes (peplomers)

True or False: Spikes give the viruses host specificity/infectivity.

true

What is the nucleic acid shape in viruses?

linear, circular, or segmented

DNA and RNA can be ___ or ___ in viruses.

double stranded or single stranded

True or False: There is more DNA viruses than RNA viruses.

false - more RNA

What group is excluded from RNA virus (ribovirus)?

retrovirus

What is the + sense in viruses?

same as mRNA, ready for translation therefore protein synthesis

What is the - sense in viruses?

complementary to mRNA, need additional proccessing

What is a virion's enzyme?

RNA-dependent RNA polymerase