Microbiology chapter 6

capsomeres

- identical protein subunits that spontaneously self assemble to form the capsid helical capsid- rod-shaped capsomeres that form a continuous helix around the nucleic acid icosahedral capsid- three-dimensional, 20-sided figure with 12 evenly spaced corners

Creutzfeldt-Jakob Disease (CJD)

-affects the central nervous system of humans -causes gradual degeneration and death -transmissible by an unknown mechanism -several animals are victims of similar diseases scrapie: sheep, mink elk bovine spongiform encephalopathy: cows

spongiform encephalopathies

-chronic, persistent disease in humans and animals -brain tissue removed from affected animals resembles a sponge

plaques

-clear, well-defined patches in the cell sheet -develops when viruses released from an infected cell radiate out to surrounding cells and infect them -infection spreads gradually and symmetrically from the original point of infection

prions

-common feature of spongiform encephalopathies -distinct protein fibrils deposited in brain tissue of affected animals

detecting viral growth in cultures

-degeneration and lysis of infected cells -plaques

satellite virus

-dependent on other viruses for replication -adeno-associated virus (AAV)

benefits of using bird embryos

-embryonic development occurs in a protective shell -intact and self-supporting unit with its own sterile environment and nourishment -furnishes several embryonic tissues that support viral multiplication

prion infections

-exact mode of infection is unknown -protein composition of prions has revolutionized ideas of what can constitute an infectious agent -questions about how prions replicate given that they have no nucleic acid

primary cell cultures

-freshly isolated animal tissue is placed in a growth medium -cells undergo mitotic division, producing a monolayer -retain the characteristics of the original tissue from which they were derived

continuous cell cultures

-have altered chromosome numbers -grow rapidly -show changes in morphology -can be continuously subcultured if they are given fresh nutrient media

Interferon (IFN)

-naturally occurring human cell product -used with some success in preventing and treating viral infections

Viral budding or exocytosis

-nucleocapsid binds to the membrane -small pouch is formed -pinching off of the pouch releases the virus with its envelope -viruses are shed gradually without destruction of the cell

lysogenic conversion

-the acquisition of a new trait from a temperate phage -responsible for the diphtheria toxin, cholera toxin, and botulism toxin

transformation

-virus carries genes that directly cause cancer -virus produces proteins that induce a loss of growth regulation in the cell

viroid

-virus-like agent that parasitizes plants -about one-tenth the size of an average virus -composed only of naked strands of RNA - lack a capsid or other type of coating -significant pathogens in economically important plants: tomatoes, potatoes, cucumbers, citrus trees, and chrysanthemums

-Viruses mutate at a rapid rate -Difficult to design therapies against viruses -Scientists focus on developing vaccines against viruses since so few antiviral drugs are available and antibiotics are ineffective

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Describe the difference between primary and continuous cell lines.

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Describe the differences between the lytic and lysogenic phase of viral replication.

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List three unique forms or viral nucleic acid.

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Occasionally, phage genes in the bacterial chromosome cause the production of toxins or enzymes that cause pathology in the human

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general phases in the life cycle of animal viruses

1. adsorption 2. penetration 3. uncoating 4. synthesis 5. assembly 6. release from host cel

List and describe the main steps of animal virus replication.

1. adsorption 2. penetration 3. uncoating 4. synthesis 5. assembly 6. release from host cell

What percentage of the bacterial chromosome is composed of viral genes?

10-20%

lytic cycle

: life cycle of bacteriophage that ends in destruction of the bacterial cell

Standard virus classification systems use all of the following except: genetic makeup structure disease caused chemical composition

A virus name ending in -viridae denotes a viral genus family

What is the protein shell that surrounds a viral genome called?

Capsid

What is the difference between DNA virus replication and RNA virus replication?

DNA viral replication occurs in the nucleus, while RNA viral replication occurs in the cytoplasm (ribosomes)

True/False: Viruses are alive.

False

True/False: Viruses that infect animal cells can never infect human cells.

False

True/False: The term plaques is only used to describe the effects of bacteriophage on cell cultures.

False - all viruses produce plaques

True/False: Viruses can be seen with a light microscope.

False - need an electron microscope

True/False: Viruses can be cultured using the same methods as bacteria and fungi.

False; need living host such as chick embryo

Unique properties of viruses

Infectious particles; rather than organisms Active or inactive; rather than alive or dead Obligate intracellular parasites: -cannot multiply unless they invade a specific host cell -must instruct the genetic and metabolic machinery of the host cell to make and release new viruses

Viral enzymes

Located in nucleocapsid-polymerases and replicases reverse transcriptase Located in envelope-hemagglutinin neuraminidase

negative-sense RNA

RNA genomes that need to be converted into the proper form to be made into proteins

Pasteur developed a vaccine for the _______ virus

Rabies

Pasteur developed a vaccine for which virus?

Rabies; coined the term "virus"

host range

a virus can invade its host cell only through making an exact fit with a specific host molecule -restricted host range: hepatitis B only infects liver cells of humans -intermediate host range: poliovirus infects intestinal and nerve cells of primates -broad host range: rabies virus infects various cells of all mammals

induction

activation of a prophage in a lysogenic cell to undergo the lytic cycle

prophage

an inactive state in which phage DNA is inserted into the host chromosome

Viruses were discovered by filtering infectious fluid through a filter designed to trap ________.

bacteria

lysogenic cycle

bacteriophage becomes incorporated into the host cell DNA

nucleocapsid

capsid and nucleic acid together

viral envelope

cell membrane or nuclear membrane. regular membrane proteins are replaced with viral proteins. spikes: protruding glycoproteins essential for attachment to the host cell.

The influenza virus has traditionally been cultured in ________.

chick embryos

inclusion bodies

compacted masses of viruses or damaged cell organelles in the nucleus or cytoplasm

naked virus

consists only of a nucleocapsid

Loeffler and Frosch

discovered foot-and-mouth disease caused by virus

Ivanovski and Beijernick

discovered that tobacco disease caused by virus

pocks

discrete, opaque spots indicating localized areas of damage

endocytosis

entire virus is engulfed by a cell and enclosed in a vacuole or vesicle

uncoating

enzymes in the vacuole dissolve the envelope and capsid, releasing the virus into the cytoplasm

oncogenic viruses

experts say about 20% of human cancers are caused by viruses

True/False: Viral mutation rates are low and viruses are easy to track in a population.

false

spikes

found on both naked and enveloped viruses project from either the nucleocapsid or envelope allow viruses to dock with their host cells spikes: protruding glycoproteins essential for attachment to the host cell

virion

fully formed virus able to establish infection in a host

syncytia

fusion of multiple host cells into single large cells containing multiple nuclei

complex capsids

have multiple types of proteins, shape is non-symmetrical found in bacteriophages

temperate phages

have the ability to undergo adsorption and penetration but do not immediately undergo replication or release

Describe the structures of icosahedral, helical, and complex viruses.

helical capsid- rod-shaped capsomeres that form a continuous helix around the nucleic acid icosahedral capsid- three-dimensional, 20-sided figure with 12 evenly spaced corners complex capsid - have multiple types of proteins, shape is nonsymmetrical, found in bacteriophages

cell culture of tissue culture

in vitro cultivation systems -simple and effective way to grow populations of isolated animal cells in culture dishes -most viruses are propagated through cell culture -much of a virologist's work involves developing and maintaining cultures

filterable virus

infectious fluids were passed through filters designed to trap bacteria. the cell-free fluid remained infectious = proved that an agent smaller than bacteria was the cause of disease

Discuss the predominant view among scientists as to the nature of viruses.

infectious particle

the primary purposes of viral cultivation

isolate and identify make vaccines research

List and describe 5 unique properties of viruses.

not alive, do not reproduce on their own, very small, ... core contains nucleic acids,

Satellite viruses require ________ in order to multiply.

other viruses

chronic latent stage

periodic activation after a period of viral inactivity

Prions are composed of

protein

RNA viruses

replicate in the cytoplasm

DNA viruses

replicate in the nucleus

capsid

shell surrounds the nucleic acid

positive-sense RNA

single-stranded RNA genomes ready for immediate translation into proteins

Viral capsids are constructed from ________ subunits.

structural, capsomere

reverse transcriptase

synthesizes DNA from RNA

How are the infectious cycles of viruses different in bacterial and eukaryotic host cells?

the capsid does not enter a bacterium

genome

the full complement of DNA and RNA carried by a cell

adsorb

to attach, i.e. a virus adsorbs to a specific protein receptor

True/False: Viral infections are more common than bacterial infections.

true

virus size

ultra microscopic size electron microscope required to see them parvoviruses: 20 nm in diameter mimiviruses: 450 nm in length - larger than some small bacteria cylindrical viruses: 800 nm long, but 15 nm in diameter

envelope

usually a modified piece of the host cell membrane

Doctors and scientists most often rely on _________ to treat or prevent viral infections:

vaccines

provirus

viral DNA incorporated into the DNA of the host

in vitro methods

viral cultivation in cell or tissue culture

in vivo methods

viral cultivation in lab animals or embryonic bird tissues

_________ infect plants.

viroids

Cytopathic Effects (CPE's)

virus-induced damage to the cell that alters its microscopic appearance cells can become disoriented, undergo major changes in shape or size, or develop intracellular damage

bacteriophage

viruses that invade bacteria -discovered in 1915 by Frederick Twort and Felix d'Herelle -parasitize every known bacterial species -often make the bacteria they infect more pathogenic for humans