MICROPARA 4 Flashcards
Complete virus particles, called
virions
Most viruses range in size from to
nm in diameter
10 to 300
what virus—can
be up to 1 µm in length
Ebola
The smallest virus is about the size
of the
large hemoglobin molecule of a red blood cell
The first
photographs of viruses were obtained in
1940.
A ____ procedure, developed in 1959, coupled with
transmission electron microscopy, revolutionized the study
of viruses, making it possible to observe unstained viruses
against an electron-dense, dark background.
negative staining
Viruses are extremely small. They are observed using
___ microscopes.
electron
Some viruses—called _—cause
specific types of cancer, including human cancers such as
lymphomas, carcinomas, and some types of leukemia.
oncogenic viruses or oncoviruses
A typical virion consists of a genome of either DNA or
RNA, surrounded by a _
capsid (protein coat)
capsid (protein coat), which is
composed of many small protein units called
capsomeres
Together, the nucleic acid and the capsid
are referred to as the
nucleocapsid
polyhedral
(many sided)
helical
(coiled
tubes)
Polyhedral capsids have ) sides or facets
20
The ____ theory”: viruses originated in the
primordial soup and coevolved with bacteria and
archaea. This hypothesis has few supporters
“coevolution
The __ theory”: viruses evolved
from free-living prokaryotes that invaded other living
organisms, and gradually lost functions that were
provided by the host cell. This theory has little
support
retrograde evolution theory”
The “___theory”: viruses are pieces of host
cell RNA or DNA that have escaped from living cells
and are no longer under cellular control. Of the three
theories, this is currently the most widely accepted
explanation for the origin of viruses.
“escaped gene theory”
Viruses that infect humans and animals are collectively
referred to as
animal viruses.
Steps in the Multiplication of Animal Viruses
1 Attachment (adsorption)
The virus attaches to a protein or polysaccharide molecule (receptor) on the surface of a host cell
2 Penetration The entire virus enters the host cell, in some cases because it was phagocytized by the cell
3 Uncoating The viral nucleic acid escapes from the capsid
4 Biosynthesis Viral genes are expressed, resulting in the production of pieces or parts of viruses (i.e., viral DNA and viral proteins)
5 Assembly The viral pieces or parts are assembled to create complete virions
6 Release The complete virions escape from the host cell by lysis or budding
The virus attaches to a protein or polysaccharide
molecule (receptor) on the surface of a host cell
Attachment
(adsorption)
The entire virus enters the host cell, in some cases
because it was phagocytized by the cell
Penetration
The viral nucleic acid escapes from the capsid
Uncoating
Viral genes are expressed, resulting in the
production of pieces or parts of viruses (i.e., viral
DNA and viral proteins)
Biosynthesis
The viral pieces or parts are assembled to create
complete virions
Assembly
The complete virions escape from the host cell by
lysis or budding
Release
Animal viruses escape from their host cells by either____.
lysis
of the cell or budding
Remnants or collections of viruses, called , are often seen in infected cells and are used as a
diagnostic tool to identify certain viral diseases.
inclusion
bodies
Viruses that escape by budding
become____ viruses.
enveloped
Cells infected with
Cytomegalovirus (CMV) demonstrate intranuclear inclusion
bodies referred to as
“owl eyes”
In rabies, the cytoplasmic inclusion bodies in nerve cells are
called
Negri bodies
The first evidence that viruses cause cancers
came from experiments with
chickens.
Drugs used to treat viral infections are called
antiviral
agents.