CHP 13 General Morphology
General Characteristics of Viruses ● Helical viruses = hollow cylinders surrounding nucleic acid
● may be regarded as exceptionally complex aggregations of nonliving ● Polyhedral viruses = many-sided
chemicals or as exceptionally simple living microbes ● Enveloped viruses = covered by an envelope & roughly spherical but
● Viruses contain single type of nucleic acid (DNA or RNA) and protein highly pleomorphic
coat, sometimes enclosed by an envelope composed of lipids, ● Complex viruses have complex structures. Ex. many bacteriophages
proteins, and carbohydrates have a polyhedral capsid with a helical tail attached
● Viruses are obligate intracellular parasites. They multiply by using Taxonomy of Viruses
host cell’s synthesizing machinery to cause synthesis of specialized ● Classification of viruses is based on type of nucleic acid & strategy
elements that can transfer viral nucleic acid to other cells for replication
Host Range ● Virus family names end in -viridae; genus names end in -virus;
● refers to spectrum of host cells a virus can infect order names end in -ales
● Most viruses infect only specific types of cells in 1 host species ● Viral species = group of viruses sharing the same genetic
● determined by specific attachment site on the host cell’s surface and information & ecological niche
the availability of host cellular factors Isolation, Cultivation, & Identification of Viruses
Viral Size ● Viruses must be grown in living cells
● Viral size is ascertained by electron microscopy ● The easiest viruses to grow are bacteriophages (form plaques)
● Viruses range from 20 to 1000 nm in length Growing Bacteriophages in the Laboratory
Viral Structure ● The plaque method mixes bacteriophages w/ host bacteria &
● A virion is a complete, fully developed viral particle composed of nutrient agar
nucleic acid surrounded by protein coat ● After several viral multiplication cycles, bacteria in the area around
Nucleic Acid the original virus are destroyed; area of lysis is called plaque
● Viruses contain either DNA OR RNA, NEVER both, and the nucleic ● Each plaque originates corresponds to single virus; expressed as
acid may be single- or double-stranded, linear or circular, or divided plaque-forming units (PFU)
into several separate molecules Growing Animal Viruses in the Laboratory
● The proportion of nucleic acid in relation to protein in viruses ranges ● Cultivation of some animal viruses requires whole animals
from about 1% to about 50% ● Simian AIDS & feline AIDS provide models for studying human AIDS
Capsid & Envelope ● Some animal viruses can be cultivated in embryonated eggs
● Capsid = protein coat surrounding nucleic acid of a virus ● Cell cultures are animal or plant cells growing in culture media
● The capsid is composed of subunits, capsomeres, which can be a ● Viral growth are detected via cytopathic effects (deterioration) in
single type of protein or several types cell culture; continuous cell lines used
● Capsid of some viruses is enclosed by an envelope consisting of Viral Identification
, lipids, proteins, and carbohydrates ● Cytopathic effects = deterioration
● Some envelopes are covered with carbohydrate-protein complexes ● Serological tests = western blotting - reaction of virus w/ antibodies
called spikes
General Characteristics of Viruses ● Helical viruses = hollow cylinders surrounding nucleic acid
● may be regarded as exceptionally complex aggregations of nonliving ● Polyhedral viruses = many-sided
chemicals or as exceptionally simple living microbes ● Enveloped viruses = covered by an envelope & roughly spherical but
● Viruses contain single type of nucleic acid (DNA or RNA) and protein highly pleomorphic
coat, sometimes enclosed by an envelope composed of lipids, ● Complex viruses have complex structures. Ex. many bacteriophages
proteins, and carbohydrates have a polyhedral capsid with a helical tail attached
● Viruses are obligate intracellular parasites. They multiply by using Taxonomy of Viruses
host cell’s synthesizing machinery to cause synthesis of specialized ● Classification of viruses is based on type of nucleic acid & strategy
elements that can transfer viral nucleic acid to other cells for replication
Host Range ● Virus family names end in -viridae; genus names end in -virus;
● refers to spectrum of host cells a virus can infect order names end in -ales
● Most viruses infect only specific types of cells in 1 host species ● Viral species = group of viruses sharing the same genetic
● determined by specific attachment site on the host cell’s surface and information & ecological niche
the availability of host cellular factors Isolation, Cultivation, & Identification of Viruses
Viral Size ● Viruses must be grown in living cells
● Viral size is ascertained by electron microscopy ● The easiest viruses to grow are bacteriophages (form plaques)
● Viruses range from 20 to 1000 nm in length Growing Bacteriophages in the Laboratory
Viral Structure ● The plaque method mixes bacteriophages w/ host bacteria &
● A virion is a complete, fully developed viral particle composed of nutrient agar
nucleic acid surrounded by protein coat ● After several viral multiplication cycles, bacteria in the area around
Nucleic Acid the original virus are destroyed; area of lysis is called plaque
● Viruses contain either DNA OR RNA, NEVER both, and the nucleic ● Each plaque originates corresponds to single virus; expressed as
acid may be single- or double-stranded, linear or circular, or divided plaque-forming units (PFU)
into several separate molecules Growing Animal Viruses in the Laboratory
● The proportion of nucleic acid in relation to protein in viruses ranges ● Cultivation of some animal viruses requires whole animals
from about 1% to about 50% ● Simian AIDS & feline AIDS provide models for studying human AIDS
Capsid & Envelope ● Some animal viruses can be cultivated in embryonated eggs
● Capsid = protein coat surrounding nucleic acid of a virus ● Cell cultures are animal or plant cells growing in culture media
● The capsid is composed of subunits, capsomeres, which can be a ● Viral growth are detected via cytopathic effects (deterioration) in
single type of protein or several types cell culture; continuous cell lines used
● Capsid of some viruses is enclosed by an envelope consisting of Viral Identification
, lipids, proteins, and carbohydrates ● Cytopathic effects = deterioration
● Some envelopes are covered with carbohydrate-protein complexes ● Serological tests = western blotting - reaction of virus w/ antibodies
called spikes
