13. Characterizing And Classifying Viruses, Viroids, And Prions Flashcards
Virus: extracellular state
___,___,___
Virion
Capsid
Envelope
Virus
Minuscule, acellular, infectious agent usually having one or several pieces of nucleic acid (either DNA or RNA)
Virus: intracellular state
Capsid removes
Virus exists as nucleic acid
Virion
A virus when outside a cell
Capsid
Protein coat surrounding a nucleic a core
Envelope
Phospholipid membrane that surrounds the capsid of some virions
Genetic material of viruses
Primary way scientists categorize and classify viruses
dsDNA, ssDNA, dsRNA, ssRNA
How can viruses be specific for a host cell
Due to affinity of viral surface proteins for complementary proteins on host cell surface
Structure & function of capsid
Composed of proteinaceous subunits called capsomeres.
Provide protection for viral nucleic acid
Structure & function of viral envelope
All viruses lack cell membranes
Play role in host recognition
Characteristics used to classify viruses
Type of nucleic acid Presence/absence of envelope Shape Size Relationship between viruses Named for special characteristics
Lytic replication in bacteriophages
Viral replication usually results in death and lysis of host cell
-attachment, entry, synthesis, assembly, release
Lysogeny
Modified replication cycle in which infected host cell grow and reproduce normally for many generations before they lyse
Bacteriophage replication
Lytic, lysogenic
Animal virus replication differs from bacteriophages because…
Presence of envelopes around some of the viruses
3 mechanisms of entry of animal viruses
Direct penetration
Membrane fusion
Endocytosis
Budding in animal viruses
Viral release where virions are extruded from host cell and acquire a portion of membrane which becomes viral envelope
Latency of animal viruses
When animal viruses remain dormant in in host cells
Neoplasia
Uncontrolled cell division in multicellular animal
Tumor
Mass of neoplastic cells
Malignant
Cancers: invade other tissues
Metastasis
Process of tumors spreading
Benign
Remain in one place, lass harmful
Viruses cause 20-25% of human cancers. T/F?
True
3 ways of culturing viruses
Media consisting of mature organisms
Embryonated eggs
Cell cultures
Problems with culturing viruses
Have to grow in living animals or cells, ethical problems with housing animals, expensive to house animals, some viruses only infect humans and difficult to grow
Viroids
Extremely small circular pieces of RNA that are infectious and pathogenic in plants
(Not viruses because lack capsids)
ONLY IN PLANTS
Prions
Proteinaceous infective particles
Do not contain nucleic acids like viruses
Very different type of infection
Diseases caused by prions
Creutzfeldt-Jakob Mad cow Chronic wasting disease Scrapie Kuru
