Micro CH 13: Characterizing + Classifying Viruses, Viroids, and Prions

Viruses

Miniscule acellular infectious agents, cause disease, don’t grow/reproduce independently

Analysis of a viral particle’s nucleic acid reveals a composition of 20%A, 20%G, 30%T, and 30%C. What type of nucleic acid does this viral particle have?

ssDNA

What is the name of the proteinaceous subunit that makes up the viral capsid?

capsomere

If one virus particle infects a cell, approximately how many infectious virus particles are present during the synthesis step of the replication cycle?

0

What event results in induction of a lysogenic bacterium?

damage to DNA

Which of the following is not a way that viruses can cause human cancer?

viruses can cause abnormalities in the host cytoplasmic membrane

How do disease-causing prions produce more disease-causing prions?

they change the shape of cellular PrP

A virion is composed of a/n

Capsid, nucleic acid core

Which statement most accurately describes lytic viral replication?

Viral replication usually results in the death by lysis of the host cell

Can a lysogenic virus ever switch to the lytic replication cycle?

Yes; it can switch only after the viral DNA is excised from the host genome by induction

What are viroids?

Small circular pieces of RNA that are infectious to plants

All prion diseases result in what symptoms?

Fatal neurological degeneration

Virion

Extracellular state

Capsid

Protein coat surrounding nucleic acids

Nucleocapsid

Nucleic acid + capsid

Intracellular state

capsid removed, virus exists as nucleic acid

genetic material of viruses

could be RNA or DNA (dsDNA, dsRNA, ssRNA), may be linear and segmented or single and circular, smaller than genomes

capsid morphology

provides protection for viral nucleic acid

capsomeres

proteinaceous subunits that compose capsid

virion shapes

helical, polyhedral, complex

hosts of viruses

only particular cells, specific

generalists

infect many kinds of cells/hosts

viral envelope

acquired from host cell during replication or release, composed of phospholipid bilayer and proteins

virus classification based on

type of nucleic acid, presence of envelope, shape, size

viral replication

dependent on hosts organelles and enzymes to produce new virions

lytic replication

viral replication results in death and lysis of host cell

5 stages of lytic replication cycle

attachment, entry, synthesis, assembly, release

lysogenic replication

infected host cells grow and reproduce normally for generations before the lyse

lysogenic conversion

results when phages carry genes that alter phenotype of a bacterium

differences in animal virus replication

presence of envelope around virus, eukaryotic nature of animal cells, lack of cell wall in animal cells

attachment of virus

chemical attraction between viral protein and cell receptor, glycoprotein spikes

enter host cell 3 ways

direct penetration, membrane fusion, endocytosis

DNA virus enters in

Nucleus

RNA virus enters in

cytoplasm

dsDNA

viral genome replicated in nucleus, viral proteins made in cytoplasm

Hepatitis B viruses

replicate DNA from RNA intermediary

ssDNA viruses

cells do not use SSDNA, pparoviruses have ssDNA genomes

positive sense viral RNA

can act as mRNA

negative sense viral RNA

cannot be directly translated

FOur types of RNA animal viruses

+ssRNA, retroviruses, -ssRNA, dsRNA

retroviruses

use DNA intermediary transcribed by viral reverse transcriptase as template to produce viral genomes

Enveloped viruses

cause persistent infections

naked viruses

released by exocytosis or lysis

latent viruses or proviruses

when animal viruses remain dormant in host cells

cancer

cell division under strict control, some cells no longer divide

neoplasia

uncontrolled cell division in multicellular animal

malignant tumors

cancers

metastasis

tumors spread

proto-oncogenes

promote cell growth + division

environmental factors contributing to activation of oncogenes

UV light, radiation, carcinogens, viruses

prion diseases

transmitted by ingestion, transplantation, contact with infected tissue

spongiform encephalopathies

large vacuoles form in brain, spongy appearance (BSE, scrapie, kury, CWD, vCJI)

prions destroyed by 

incineration, autoclaving in concentrated sodium hydroxide