Viruses, Viroids, and Prions: A Comprehensive Overview
undefined
VIRUSES, VIROIDS & PRIONS
Discovery of Viruses
Discovery of Viruses
•
Beijerinck (1897) coined the
Latin name “virus” meaning poison
•
He studied filtered plant juices
& found they caused healthy
plants to become sick
Introduction
Viruses, viroids, and prions
•
Acellular (noncellular)
•
Disease-causing agents
•
Lack cell structure
•
Cannot metabolize, grow, reproduce, or respond to their environment.
•
They must recruit the cell's metabolic chemicals and ribosomes in order
to increase their numbers
Viruses
•
A virus is a miniscule, acellular, infectious agent
•
It has one or several pieces of nucleic acid -either DNA or RNA, but never both.
•
Viruses have
no cytoplasmic membrane
, and with one exception
lack organelles
and cytosol.
•
In its extracellular state, a virus is called a virion.
•
It consists of a protein coat, called a capsid, surrounding a nucleic acid core.
•
Together the nucleic acid and its capsid are called a
nucleocapsid
.
•
Some virions have a phospholipid membrane called an
envelope
surrounding the
nucleocapsid.
•
When a virus penetrates a cell, the intracellular state is initiated; the capsid is
removed.
•
A virus without a capsid exists solely as nucleic acid but is still referred to as a
virus.
Genetic Material of Viruses
•
The
genome
of viruses includes either
DNA or RNA
, but never both.
•
In addition, they may be double-stranded (ds) or single-stranded (ss).
•
Thus, viral genomes are described as dsDNA, ssDNA, dsRNA, or ssRNA .
•
They may exist as
multiple linear
molecules of nucleic acid, or
circular and
singular
molecules of nucleic acid, depending on the type of virus.
•
Viral genomes are usually much smaller than the genomes of cells. The
smallest
chlamydiaI
bacterium has almost 1000 genes; the genome of
bacteriophage
MSZ
has only three genes.
Hosts of Viruses
•
Most viruses infect only particular kinds of cells.
•
This
specificity
is due to the affinity of viral surface proteins or
glycoproteins for complementary proteins or glycoproteins on the surface
of the host cell.
•
A virus that infects bacteria is referred to as a bacteriophage, or simply a
phage.
•
Viruses also infect humans, other animals, plants, and even fungi.
Sizes of Viruses
•
Viruses are so small that most cannot be seen by light microscopy.
•
The smallest have a diameter of 10 nm, whereas the largest are approximately
400 nm, about the size of the smallest bacterial cell.
CAPSID MORPHOLOGY
The capsid of a virus is composed of proteinaceous subunits called capsomeres.
These may be composed of only a single type of protein, or of several different
protein molecules.
VIRAL SHAPES
There are three basic types of viral shapes:
•
Helical viruses
have capsomeres that spiral around the nucleic acid,
forming a tube-like structure;
•
Polyhedral viruses
are roughly spherical, with a shape similar to a
geodesic dome; and
•
Complex viruses
have capsids of many different shapes.
THE VIRAL ENVELOPE
•
Some viruses have a membrane similar in composition to a cell membrane
surrounding their capsids. This membrane is called an envelope.
•
A virus with a membrane is called an enveloped virion.
•
A virion without an envelope is a nonenveloped or naked virion.
Viroids & Prions
Viroids & Prions
Viroids
Viroids
•
Theodor Diener
discovered
Viroids
In 1971
•
An acellular particle meaning “
virus-like
.”
•
Viroids
consist
only
of a short strand of
circular RNA
capable of self-replication.
•
Unlike viruses, viroids
do not have a protein coat
to
protect their genetic information.
Viroid Diseases
•
Potato tuber spindle disease
, which causes
slower sprouting and various deformities in
potato plants
•
Tomato planta macho viroid (TPMVd)
infects
tomato plants, which causes loss of
chlorophyll, disfigured and brittle leaves, and
very small tomatoes, resulting in loss of
productivity in this field crop.
•
Avocado sunblotch viroid (ASBVd)
results in
lower yields and poorer-quality fruit. ASBVd is
the smallest viroid discovered that infects
plants.
Prions
Prions
•
Prions are “infectious proteins”
•
In 1982,
Stanley Prusiner
, a medical doctor discovered
prions
(
received the
Nobel Prize in Physiology or Medicine in 1997.
)
•
Proteins are acellular hence….
•
Do not contain DNA or RNA.
14
•
A prion is a misfolded rogue form of a normal protein (PrPc).
•
PrPsc may be caused by a
genetic mutation
or
occur spontaneously
•
PrPsc can be infectious,
•
They can
stimulate
other endogenous
normal proteins
to become
misfolded.
Prions
Prions
Prion Diseases
Prion Diseases
P
r
i
o
n
s
c
a
u
s
e
v
a
r
i
o
u
s
f
o
r
m
s
o
f
t
r
a
n
s
m
i
s
s
i
b
l
e
s
p
o
n
g
i
f
o
r
m
e
n
c
e
p
h
a
l
o
p
a
t
h
y
(
T
S
E
)
i
n
h
u
m
a
n
a
n
d
a
n
i
m
a
l
s
.
TSE affects the brain and nervous system.
It causes the brain tissue to become sponge-like
Kills brain cells
Forms holes in the tissue
Leads to brain damage, loss of motor coordination, and dementia.
Infected individuals are mentally impaired and become unable to move or speak.
There is no cure, and the disease progresses rapidly, eventually leads to death.
•
TSEs in humans include
kuru
,
fatal familial insomnia
,
Gerstmann-
Straussler-Scheinker disease
, and
Creutzfeldt-Jakob disease
.
•
TSEs in animals include
mad cow disease
,
scrapie
(in sheep and goats),
and
chronic wasting disease
(in elk and deer).
TSEs can be transmitted between animals and from animals to humans by eating
contaminated meat or animal feed.
Explore the fascinating world of viruses, viroids, and prions, from their discovery to their genetic material and hosts. Learn about the structure, genome, and sizes of viruses, as well as their interactions with different host cells. Gain insights into these acellular disease-causing agents and their unique characteristics.
Download Presentation
Please find below an Image/Link to download the presentation.
The content on the website is provided AS IS for your information and personal use only. It may not be sold, licensed, or shared on other websites without obtaining consent from the author. Download presentation by click this link. If you encounter any issues during the download, it is possible that the publisher has removed the file from their server.
E N D
Presentation Transcript
Discovery of Viruses Beijerinck (1897) coined the Latin name virus meaning poison He studied filtered plant juices & found they caused healthy plants to become sick
Introduction Viruses, viroids, and prions Acellular (noncellular) Disease-causing agents Lack cell structure Cannot metabolize, grow, reproduce, or respond to their environment. They must recruit the cell's metabolic chemicals and ribosomes in order to increase their numbers
Viruses A virus is a miniscule, acellular, infectious agent It has one or several pieces of nucleic acid -either DNA or RNA, but never both. Viruses have no cytoplasmic membrane, and with one exception lack organelles and cytosol. In its extracellular state, a virus is called a virion. It consists of a protein coat, called a capsid, surrounding a nucleic acid core. Together the nucleic acid and its capsid are called a nucleocapsid. Some virions have a phospholipid membrane called an envelope surrounding the nucleocapsid. When a virus penetrates a cell, the intracellular state is initiated; the capsid is removed. A virus without a capsid exists solely as nucleic acid but is still referred to as a virus.
Genetic Material of Viruses The genome of viruses includes either DNA or RNA, but never both. In addition, they may be double-stranded (ds) or single-stranded (ss). Thus, viral genomes are described as dsDNA, ssDNA, dsRNA, or ssRNA . They may exist as multiple linear molecules of nucleic acid, or circular and singular molecules of nucleic acid, depending on the type of virus. Viral genomes are usually much smaller than the genomes of cells. The smallest chlamydiaI bacterium has almost 1000 genes; the genome of bacteriophage MSZ has only three genes.
Hosts of Viruses Most viruses infect only particular kinds of cells. This specificity is due to the affinity of viral surface proteins or glycoproteins for complementary proteins or glycoproteins on the surface of the host cell. A virus that infects bacteria is referred to as a bacteriophage, or simply a phage. Viruses also infect humans, other animals, plants, and even fungi.
Sizes of Viruses Viruses are so small that most cannot be seen by light microscopy. The smallest have a diameter of 10 nm, whereas the largest are approximately 400 nm, about the size of the smallest bacterial cell.
Viroids Theodor Theodor Diener An acellular particle meaning virus-like. Viroids Viroids consist only of a short strand of circular RNA capable of self-replication. Unlike viruses, viroids do not have a protein coat to protect their genetic information. Diener discovered Viroids Viroids In 1971
Viroid Diseases Potato tuber spindle disease Potato tuber spindle disease, which causes slower sprouting and various deformities in potato plants Tomato planta macho viroid ( Tomato planta macho viroid (TPMVd tomato plants, which causes loss of chlorophyll, disfigured and brittle leaves, and very small tomatoes, resulting in loss of productivity in this field crop. Avocado Avocado sunblotch sunblotch viroid ( viroid (ASBVd lower yields and poorer-quality fruit. ASBVd is the smallest viroid discovered that infects plants. TPMVd) ) infects ASBVd) ) results in
Prions Prions are infectious proteins In 1982, Stanley Stanley Prusiner Nobel Prize in Physiology or Medicine in 1997.) Proteins are acellular hence . Do not contain DNA or RNA. Prusiner, a medical doctor discovered prions prions (received the 14
Prions A prion is a misfolded rogue form of a normal protein (PrPc). PrPsc may be caused by a genetic mutation or occur spontaneously PrPsc can be infectious, They can stimulate other endogenous normal proteins to become misfolded.
Prion Diseases Prions cause various forms of transmissible spongiform encephalopathy (TSE) in human and animals. TSE affects the brain and nervous system. It causes the brain tissue to become sponge-like Kills brain cells Forms holes in the tissue Leads to brain damage, loss of motor coordination, and dementia. Infected individuals are mentally impaired and become unable to move or speak. There is no cure, and the disease progresses rapidly, eventually leads to death. There is no cure, and the disease progresses rapidly, eventually leads to death.
TSEs in humans include kuru Straussler Straussler- -Scheinker Scheinker disease TSEs in animals include mad cow disease and chronic wasting disease chronic wasting disease (in elk and deer). kuru, fatal familial insomnia fatal familial insomnia, Gerstmann disease, and Creutzfeldt Creutzfeldt- -Jakob disease Gerstmann- - Jakob disease. mad cow disease, scrapie scrapie (in sheep and goats), TSEs can be transmitted between animals and from animals to humans by eating contaminated meat or animal feed.
