Studied by 3 people
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Learning objectives
•Describe why viruses are not considered living organisms
•Be able to describe and explain the basic structure of a virus, and additionally know the various types of these structures/classifications
Characteristics of life
Organization, Homeostasis, Growth and Metabolism, Response to stimuli, Heredity, Reproduction, Evolution and Adaptation
Properties viruses share with life
Exhibit structural organization
Contain genetic material
Contain a replicative life cycle Evolve over time
Properties of life that viruses lack
Are not comprised of cells
Lack homeostasis Have no growth or metabolism
Do not respond to stimuli
Cannot reproduce without the use of host cell machinery
virus
a non-living obligate intracellular parasite
virion
a virus that is extracellular
viral genome
DNA or RNA, varies considerably in size and organization
Sense DNA
DNA or RNA, varies considerably in size and organization
antisense DNA
Template-strand of DNA that gets transcribed
Sense RNA (+RNA)
mRNA that is translated into a protein
Antisense RNA (-RNA)
RNA that is a complimentary strand to translated mRNA
Central Dogma
Antisense DNA is transcribed into Sense RNA (which is translated into protein)
Mutation rate
Fast mutation rates lead to new strains of the same virus
capsid
protein coat protecting the genome, may carry accessory proteins, composed of capsomeres which are made up of protomers
Helical viruses
Repeated capsomeres that form a filamentous capsid surrounding the genomic material; may be referred to as filamentous, may not always appear strictly helical (ex. Tobacco mosaic virus, Mumps virus, Ebola virus)
spherical
Has a spherical capsid/envelope; not always its own category, it is the capsid and not the presence of a spherical phospholipid membrane that make a virus spherical (ex. Influenza virus)
polyhedral
Capsomeres that form 20 faces, 12 vertices, and 30 edges; may be referred to as icosahedral, cubic, regular, or isometric (ex. Adenovirus, Herpesvirus)
complex
The “catch-all” group with no real pattern, often may have a combination of several shapes but may not necessarily be classified as such (ex. T4 Bacteriophage, Variola virus, Rabies virus)
Envelope
host-derived lipid membrane, contains host and viral proteins
Attachment proteins
glycoproteins that recognize one or more specific host cell receptors (Controls viral tropism: the spectrum of cells of a host that a virus may infect)
HIV
HIV GP120 binds to CD4 as well as CCR5 or CXCR4 found on T cells
