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.
three types of human cancers:
nasopharyngeal
carcinoma, Burkitt lymphoma, and B-cell lymphoma
HIV, the cause of AIDS, is an enveloped,
single-stranded
RNA virusa
aids is a member of a genus of viruses
called
lentiviruses in a family of viruses called Retroviridae
viral genome is referred to as a
provirus
virus is a thread-shaped virus (Fig. 4-12) that
is thought to cross over from bats to infect humans.
Ebola virus
Drugs used to treat viral infections are called
antiviral
agents.
bacteriophages: an almost spherical
shape, with 20 triangular facets; the smallest
____ phages are about 25 nm in diameter.
Icosahedron
bacteriophages: long tubes formed by
capsid proteins assembled into a helical structure;
they can be up to about 900 nm long
Filamentous
bacteriophages: icosahedral heads attached
to helical tails; they may also possess base plates and
tail fibers.
Complex
what bacteriophages always cause what is known as
the lytic cycle, which ends with the destruction (lysis) of
the bacterial cell.
Virulent
temperate
phages (also known as
lysogenic phages
The other category of bacteriophages— —do not immediately initiate the lytic cycle, but rather, their DNA
remains integrated into the bacterial cell chromosome,
generation after generation.
temperate phages
Bacteriophages were discovered independently by
Frederick Twort in 1915
and Felix d’Herelle in 1917
“bacteriophage” (phagein is Greek for
“bacteriophage” (phagein is Greek for devour)
an extremely large double-stranded DNA virus,
called ___, was recovered from amebas.
Mimivirus
The virus
was given the name Mimivirus because it
bacteria.
“mimics”
They are proposed to be placed in a new viral
order called the Megaviridae. ____ is the largest
discovered so far, almost twice as large as Mimivirus and a
genome that is capable of encoding over 2,000 genes (Fig.
4-17).
Pandoravirus
consist of short, naked
fragments of single-stranded RNA (about 300–400
nucleotides in length) that can interfere with the metabolism of plant cells and stunt the growth of plants, sometimes killing the plants in the process.
Viroids
are small infectious
proteins that cause fatal neurologic diseases in animals and
humans in which the brain becomes riddled with holes
(becomes sponge-like).
Prions
All these diseases are untreatable
and fatal and are collectively referred to as “transmissible
spongiform encephalopathies”
The human prion
diseases of kuru, Creutzfeldt–Jakob disease (CJD) and
Gerstmann–Sträussler–Scheinker syndrome
The 1997 Nobel Prize for Physiology or Medicine was
awarded to __, the scientist who coined
the term prion and studied the role of these proteinaceous
infectious particles in disease.
Stanley B. Prusiner
is a disease that was once common among natives in Papua, New
Guinea, where women and children ate human brains as part of a traditional
burial custom
Kuru
The bacteriologist’s most important reference
(sometimes referred to as the bacteriologist’s “bible”) is a
five-volume set of books entitled
Bergey’s Manual of
Systematic Bacteriology
The three general shapes of bacteria
are round (cocci),
rod-shaped (bacilli), and spiral-shaped.
According to Bergey’s Manual, the Domain Bacteria
contains organisms that are broadly divided into three
phenotypic categories
(i.e., categories based on their
physical characteristics): (a) those that are Gram-negative
and have a cell wall, (b) those that are Gram-positive and
have a cell wall, and (c) those that lack a cell wall.
Bacteria reproduce by
binary fission
The time it takes for one cell to split into two cells is
referred to as that
organism’s generation time.
Cocci may be seen singly or in pairs, chains, cluster, packet of four,or packets of eight
(diplococci, (streptococci), (staphylococci), (tetrads) (octads)
Bacteria in the genus Mycoplasma
do not have
cell walls;
Bacteria
that exist in a variety of shapes are described as being
____; the ability to exist in a variety of shapes is
known as ____
pleomorphic. pleomorphism
Because they have no cell walls,
____ are resistant to antibiotics that inhibit cell
wall synthesis.
mycoplasmas
A ____ stain is sufficient to determine bacterial shape
and morphologic arrangement
simple
______ developed a staining
technique that bears his name—the Gram stain or Gram
staining procedure
Dr. Hans Christian Gram
The ____ has become the most
important staining procedure in the bacteriology
laboratory,
Gram stain
______ is of value in the diagnosis of
tuberculosis.
The acid-fast stain
If a bacterium is able to “swim,” it is said to be
motile.
Bacteria never
possess
cilia.
cocci
are generally nonmotile or motile
non
but motile organisms will
___ from the stab line
spread away
Motility can be demonstrated by stabbing the bacteria
into a tube of semisolid agar or by using the
hanging-drop
technique.
Nonmotile organisms
will grow ___- the stab line
only along
___ are bacteria, but
they do not possess all the attributes of typical bacterial
cells. Thus, they are often referred to as “unique” or
“rudimentary” bacteria. Because they are so small and
difficult to isolate, they were formerly thought to be
viruses.
Rickettsias, chlamydias, and mycoplasmas
A mound or pile of bacteria on the surface of a solid
culture medium is known as a
bacterial colony.
The genus Rickettsia was named for
Howard T. Ricketts
are referred to as “energy parasites.”
Chlamydias
Rickettsias and chlamydias are examples of obligate
___—organisms that can exist only
within host cells.
intracellular organisms
Photosynthetic bacteria include
purple bacteria, green
bacteria, and cyanobacteria
Photosynthesis that produces oxygen is called
oxygenic
photosynthesis
photosynthesis that does not
produce oxygen is called
anoxygenic photosynthesis.
In cyanobacteria, photosynthesis
takes place on intracellular membranes known as
thylakoids
