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Microbiology > Chapter 13- Characterizing and Classifying Viruses, Viroids, and Prions > Flashcards

Chapter 13- Characterizing and Classifying Viruses, Viroids, and Prions Flashcards

1
Q

What is the definition of a virus?

A

A miniscule, acellualr, infectious agent having either DNA or RNA

Causes many infections in human, animals, plants, and bacteria

Causes of the diseases the plague the industrialized world- cold, flu, herpes, AIDS, and SARS

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2
Q

What are some characteristics of viruses?

A

Cannot carry out any metabolic pathway

Neither grow nor respond to the environment

Cannot reproduce independently- recruit cell’s metabolic pathways to increase numbers

No cytoplamic membrane, cytosol, or organelles

Have an extracellular and intracellular state

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3
Q

What are some characteristics of the extracellular state?

A

Called virion

Protein coat (capsid) surrounds the nucleic acid, nucleic acid and capsule known as nucleocapsid

Some have phsopholipid envelope

Outermost layer provides protection and recognition sites for host cells

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4
Q

What are some characteristics of the intracellular state?

A

Capsid is removed

Virus exists as nucleic acids

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5
Q

What is the genetic material of viruses?

A

Show more variety in nature of their genomes than do cells

May be used as a means of classification

EITHER DNA OR RNA, NEVER BOTH- dsDNA, ssDNA, ssRNA, dsRNA

May be either linear and segmented or single and circular

Much smaller than genomes of cells

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6
Q

What are the types of hosts for viruses?

A

Only infect a particular host’s cells- due to affinity of viral surface proteins for complementary proteins on host cell surface

May be so specific they only infect particular kind of cell in a host (HIV)

Generalists- infect many kinds of cells in many different hosts including bacteria, arachea, protozoa, fungi, plants, animals, and humans (flu virus, West Nile)

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7
Q

What is the history of viruses?

A

Ivanowski- 1892, demonstrated that viruses are acellular through the conduction of an experiment

Stanley- 1935, isolated and characterized tobacoo mosaic viruses

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8
Q

What are general characteristics of capsid morphology?

A

Capsids- protein coats that provide protection for viral nucleic acid and means of attachment to host’s cells

Composed of proteinaceous subunits called capsomeres

Capsomere may be made of single or multiple types of proteins

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9
Q

What are the characteristic shapes of a virus?

A

Polyhedral, complex, helical

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10
Q

What are enveloped viruses?

A

A virus with an outer envelope surrounding the capsid is an enveloped virion

If lacking an envelope- non-enveloped or naked virion

Matrix proteins fill the region between capsid and envelope

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11
Q

How are viral envelopes acquired by a virus?

A

Acquired from host cell during viral replication or release

Envelope is a portion of membrane system of host, composed of phospholipid bilayer and proteins

Some proteins are virally coded- glycoproteins (spikes)

Envelope’s proteins and glycoproteins often play role in host recognition

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12
Q

What are general characteristics of DNA viruses?

A

All replicate in the nucleus- except for the Pox virus (cytoplasm)

All are double strranded- except for parvoviridae (single) and hepadnaviridae (partial single or double stranded)

Includes:

Poxviridae

Herpesviridae

Papillomaviridae

Polyomaviridae

Adenoviridae

Hepadnaviridae

Parvoviridae

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13
Q

What are some characteristics of RNA viruses?

A

All single stranded except for Reoviridae

+- viral RNA can be used as mRNA without modification

    • viral RNA cannot be used by cell, must be modified

(See chart in notes)

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14
Q

What are characteristics of viral replication?

A

Dependent on hosts’ organelles and enzymes to produce new virions

Lytic replication- replication cycle that usually reasults in death and lysis of host cell

Stages- Attachment, Entry, Synthesis, Assembly, and Release

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15
Q

What is burst time?

A

Period of time require to complete the entire process of synthesis, assembly, and release

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16
Q

What is burst size?

A

Number of new virions released per lysed host cell

17
Q

What is the lysogenic life cycle of viruses?

A

Modified replication cycle- infected host cells grow and reproduce normally for generations before they lyse

Temperate phages/ lysogenic phages

Prophages- inactive phages

Lysogenic conversion- results when phages carry genes that alter phenotype of bacterium

Switch from inactive to active during induction

18
Q

What are some characteristics of animal viruses?

A

Same basic pathway as bacteriophages

Differences result from:

Presence of envelope, eukaryotic nature of animal cells, lack of cell wall

19
Q

How do animal viruses attach to the host cell?

A

Chemical attraction

Have no tails of tail fibers- instead have glycoprotein spikes or other attachment molecules that mediate attachment

Three types of attachment-

Direct penetration- non-enveloped viruses

Membrane fusion- envelope fuses with cell membrane

Endocytosis- take in envelope and virus

20
Q

How are animal viruses synthesized?

A

Each type of animal virus requires different strategy depending on nucleic acid

DNA viruses- replicate in nucleus, except for Pox virus

RNA virus- replicate in cytoplasm

Must consider- how mRNA is synthesized, what serves as template for nucleic acid replication

21
Q

How does the replication of dsDNA viruses occur?

A

Similar to normal replication of cellular DNA and translation of proteins

dsDNA - mRNA - viral proteins

22
Q

How does the replication of ssDNA viruses occur?

A

New strand of complementary DNA is made which then binds to ssDNA virus to dsDNA, replication then proceeds the same

ssDNA - dsDNA - mRNA - viral proteins

23
Q

How does replication of +ssRNA viruses occur?

A

+ssRNA serves as mRNA- translated into viral proteins

Complementary strand is synthesized by viral RNA polymerase, produces -ssRNA, serves as template to create +ssRNA genome

24
Q

How does replication of -ssRNA viruses occur?

A

Transcribe complementary strand (+ssRNA) using RNA dependent RNA transcriptase, used to make viral proteins

-ssRNA replicated from complementary strand for genome

25
Q

How does replication of dsRNA viruses occur?

A

Contains +ssRNA and -ssRNA, produced by unwinding

-ssRNA transcibed by viral RNA polymerace to make new genome

+ssRNA is translated to produce viral proteins

26
Q

How does a retrovirus replicate?

A

Positive sense RNA virus

However, do not use genome as mRNA, synthesize a DNA intermediary using reverse transcriptase enzyme

DNA serves as template for synthesis of +RNA molecules which acts as mRNA for protein synthesis

DNA able to integrate into chromosomes

Ex: HIV

27
Q

How are animal viruses assembled and released?

A

DNA viruses- in nucleus

RNA viruses- in cytoplasm

Number of viruses produced depends on the size and initial health of host cell and type of virus

28
Q

How are enveloped viruses released?

A

Released through budding

Viral glycoproteins found on cell membrane, capsid fuses with the cytoplasmic membrane, cell does not lyse

Results in continuous release of virus

29
Q

How are naked viruses released?

A

Released by exocytosis or lysis

Sudden, sharp increase in number of viruses

30
Q

What is meant by latency of animal viruses?

A

Defined as when an animal virus remains dormant in host cells, may be prolonged for years without viral activity

Some latent viruses do not become incorporated into host chromosome

Incorporation of provirus into host DNa is permanent

31
Q

How are viruses cultured?

A

3 ways:

In mature organisms- bacteria, plants, and animals

Embryonated chicken eggs- inexpensive, among largest of cells, free of contaminating microbes, nourishing yolk

Cell culture

32
Q

What are some characteristics of cell cultures?

A

Consists of cells isolated from an organism and grown on a medium or in a broth

2 Types:

Diploid cell cultures- created from embroynic plant, animal, or human cells, do not last more than 100 generations

Continuous cell cultures- longer lasting, derived from tumor cells, HeLa cell lines

33
Q

What are some characteristics of viroids?

A

Extremely small, circular pieces of RNA that are infectious and pathogenic in plants

Similar to RNA viruses but lack capsid

May appear linear due to H-bonding within the molecule

Several plant diseases are caused by viroids

34
Q

What are some characteristics of prions?

A

Proteinaceous infectious agents first decribed by Stanley Prusiner in 1982

Lack nucleic acid

35
Q

How does a prion cause disease?

A

Cellular PrP- cytoplasmic membrane protein which plays a role in normal activity of brain, made by all mammals, normally composed of alpha helices

Prion PrP- composed of beta sheets

Prion PrP converts cellular PrP into prion PrP by inducing a conformational change

36
Q

What are the diseases caused by prions?

A

Fatal neurological degeneration, fibril deposits in brain, loss of brain matter

Large vacuoles from in brain- characteristics spongy appearance

Spongiform encephalopathies- BSE, vCJD, kuru

Prions only destroyed by incineration or autoclaving in 1N NaOH

Microbiology (10 decks)

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