Chapter 6 - Viruses Microbiology

What type of organism are viruses?

acellular

What was the plant that inspired the hunt for viruses?

tobacco

Who discovered the source of tobacco mosaic disease (TMD)?

Dmitri Ivanovski

What device was used to find the TMD virus?

a porcelain filtering device

who invented the procelain filtering device?

Charles Chamberland and Louis Pasteur

How small was the filters pore size in the procelain device?

0.1 um

What can pass through the procelain filter and what can not?

bacteria over 0.2 um cannot

virus (which are very small) can

What did everyone originally think caused TMD?

very small bacteria or poison

Where does the word virus come form?

the latin word poison because that is what Ivanovski called his original TMD discovery

What microscope can be used to see viruses?

electron microscope

Do we know where viruses originated from?

no, their origin is a matter of speculation

Why are viruses not included in the taxonomy tree of life?

they are acellular and need a host cell to reproduce (obligate intracellular pathogen)

What type of pathogen is a virus?

obligate intracellular pathogen

Even though viruses do not contain a cell, what else do they contain?

genetic material

What are some examples of high power microscopy that are used to see viruses?

TEM and SEM

What are the main groups of viruses?

1. viruses

2. viroids

3. virusoids

4. prions

What was the first studied virus?

tobacco mosaic virus

what does it mean to be acellular?

not consisting of cells

In order to survive and reproduce, what do viruses need?

a host cell

What happens when the genome of a virus enters the host cell?

it directs the production of

- viral components

- proteins

- nucleic acides

that are all needed to form new virus particles

What are virions?

virus particles

What are viral components, proteins, and nucleic acids needed to produce?

virions

What do the new virions do after production?

trnasport the viral genome to another host cell and carry out another round of infection.

What are some characteristics of viruses?

- infectious and acellular

- obligate intracellular parasites with host or cell type specificity

- DNA or RNA genome (never both)

- genetic material surrounded by capsid

- lack many genes for reproduction; exploit host genome

What is the genome inside of a virus surrounded by?

a protein capsid

(in some cases, a phospholipid membrane studded with viral glycoproteins)

What does it mean to be host or cell type specific?

the virus can only attach to and infect cells of certain organisms

What type of genetic material can viruses have?

EITHER DNA or RNA

never both

Why is it hard to classify viruses?

they are always mutating and so it can be hard to place they into a set taxonomic spot

What do viruses lack and need a host cell for?

they lack many produces that are needed for reproduction so they take over the host cell and use them for reproduction

What are some examples of things viruses can infect?

They can infect everything like....

- plants

- animals

- fungi

- protists

- bacteria

- archaea

Define host range

the spectrum of host cells a virus can infect

What does it mean when a virus has a host range?

that viruses can will only be able to infect the cells of one or a few species of organism

Is having a wide host range common?

no, it is more common for a virus to only have a specific list of hosts

What are bacteriophages?

viruses that infect bacteria

What are the ways an infection can be obtained?

- direct contact

- fomite

- mechanical vector

- biological vector

What is direct contact?

person to person; infected individual

What is fomite?

An object that transmits diseases such as a door knob, microphone, etc...

What is mechanical vector?

not necessary to the life cycle of an infectious agent and merely transports it without being infected

carries the virus on the outside of the body

What is biological vector?

Not only transmit pathogens they also serve as hosts for the multiplication of a pathogen during some stage of its life cycle

organism carries virus inside

ex: ticks, mosquitoes, biting flies, etc

What is a vector?

an animal that transmits a pathogen from one host to another

What does the word bacteriophage mean?

bacteria eater

What type of cells can bacteria infect

eukaryotes and prokaryotes

What are some of the effects a virus can cause on a cell that has been infected?

abnormal growth, cell death, alteration of the genome, or even little noticeable effect in the cell.

Why are diseases hard to erradicate?

well there is very few treatments or drugs to deal with viral infections

What is an example of animal host to human host virus?

avian influenza virus

(started in birds and caused disease in humans)

what is zoonoses?

animal diseases transmitted to humans

What is reverse zoonoses?

infection of an animal that originated in a human

What is an example of zoonoses?

avian influenza virus

define virions

viral particles assembled in infected host cell

What is the range of size in virions?

between 20 nm -900 nm

What is the average size of the polio virus?

30 nm

What is the average size of the flu virus?

80-120 nm

What is the average size of the small pox virus?

~320 nm

What is the average size of a virus?

200 nm

What is used to describe the size of bacteriophages and why?

they are VERY small because they have to infect bacteria which is also very small

Why are virions different sizes?

because it depends on the type of cell they are trying to infect.

the larger the cell the bigger the virion

When someone says that there are novel giant virus species, about what size are they close to?

bacterial cells

What are the main components of viruses?

- capsid (capsomere subunit)

- genomic material (RNA or DNA)

- envelope (not all have this)

- spikes (not all have this)

Who discovered that the TMD virus was composed of RNA and proteins?

Wendell Stanley

What did Wendell Stanley's discovery contribute to?

the development of an influenza vaccine

What is a capsid?

protein coat surrounding a virus

What does the capsid surround?

the genetic material (either DNA or RNA) and/or any enzymes the virus may need

What is the capsid composed of?

protein subunits called capsomeres made of one or more different types of capsomere proteins that interlock to form the closely packed capsid

What are capsomeres?

protein subunits that make up capsids

What are the different shapes of viruses?

helical, polyhedral, and complex

What is an example of a helical virus?

TMD

What is an example of a polyhedral virus?

Human rhinovirus HRV14

What is an example of a complex virus?

variola virus

What is the main shape definition of a helical virus?

the capsid is a cylindrical or rod shape, with the genome fitting just inside the length of the capsid

What is the main shape definition of a polyhedral virus?

it consist of nucleic acid surrounded by polyhedral (many sided) capsid in the form of a icosahedron

What is a icosahedron?

a 3D, 20-sided structure with 12 verticles

ex: somewhat resemble a soccer ball

Can both helical and polyhedral shapes have envelopes?

yes

What does it mean when a virus is both helical and polyhedral?

they are described as complex

What is the basic form for a bacteriophage complex form?

the genome is located within the polyhedral head and the sheath connects the head to the tail fibers and tail pins that help the virus attach to receptors on the host cell's surface

What are tail fibers?

Help the bacteriophage to recognize and connect to the correct host cell

What are tail pins?

they are involved with recognition of specific viral "receptors" on the bacterial cell surface

What is the sheath on a virus?

contracts using the energy stored of ATO, injecting the genome into the host

In a bacteriophage, where is the genome located?

in the polyhedral head

In a bacteriophage, what attached to the bacterial host?

the tail fibers and tail pins

What are the main parts of a bacteriophage?

- capsid head

- collar

- sheath

- baseplate

- tail fibers/pins

What are the two types of envelope grouping?

enveloped viruses and naked viruses

What is an enveloped virus?

Viruses formed with a nucleic-acid packed capsid surrounded by a lipid layer

What are naked viruses?

viruses with no envelope

capsid only

What are the two types of origin a viral envelope can be?

intracellular or cytoplasmic

What are spikes on a virus?

protein structures that extend away from the capsid

What do spikes do for a virus?

allows them to attach and enter the cell

What are the two types of spikes?

Hemagglutinin (H)

Neuraminidase (N)

What does Hemagglutinin (H) mean?

it is the type of surface protein

What does neuraminidase (N) mean?

it is the type of surface protein

How are spikes used in relation to taxonomy?

Many viruses are identified by their H and N spikes

Do all viruses have spikes?

no, only certain viruses

Do all viruses have envelopes?

No, only some

What is an example of a spike identified virus?

The H1N1 avian/bird flu

What are the different genetic material cateogories?

ssDNA

dsDNA

ssRNA

dsRNA

What are the categories within ssRNA?

positive and negative strand

Since viruses are not in the tree of life, do they still require classification?

yes

What is in charge of developing, refining, and maintaining a universal taxonomy of viruses?

The International Committee on Taxonomy of Viruses (ICTV)

What are the viruses classified?

based on

- genetics

- chemistry

- morphology

- mechanisms for replicaiton

What is binomial nomenclature used for viruses?

Family: viridae

Genus: virus

When referring to a virus it is sometimes common to...

use a genus and species epithet such as

Pandoravirus dulcis

Pandoravirus salinus