MICROPARA 4 Flashcards by Hanz Myko C. DIDULO

Complete virus particles, called

virions

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Most viruses range in size from to
nm in diameter

10 to 300

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what virus—can
be up to 1 µm in length

Ebola

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The smallest virus is about the size
of the

large hemoglobin molecule of a red blood cell

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The first
photographs of viruses were obtained in

1940.

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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

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Viruses are extremely small. They are observed using
___ microscopes.

electron

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Some viruses—called _—cause
specific types of cancer, including human cancers such as
lymphomas, carcinomas, and some types of leukemia.

oncogenic viruses or oncoviruses

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A typical virion consists of a genome of either DNA or
RNA, surrounded by a _

capsid (protein coat)

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capsid (protein coat), which is
composed of many small protein units called

capsomeres

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Together, the nucleic acid and the capsid
are referred to as the

nucleocapsid

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polyhedral

(many sided)

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helical

(coiled
tubes)

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Polyhedral capsids have ) sides or facets

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The ____ theory”: viruses originated in the
primordial soup and coevolved with bacteria and
archaea. This hypothesis has few supporters

“coevolution

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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”

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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”

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Viruses that infect humans and animals are collectively
referred to as

animal viruses.

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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

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The virus attaches to a protein or polysaccharide
molecule (receptor) on the surface of a host cell

Attachment
(adsorption)

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The entire virus enters the host cell, in some cases
because it was phagocytized by the cell

Penetration

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The viral nucleic acid escapes from the capsid

Uncoating

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Viral genes are expressed, resulting in the
production of pieces or parts of viruses (i.e., viral
DNA and viral proteins)

Biosynthesis

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The viral pieces or parts are assembled to create
complete virions

Assembly

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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