Viruses Viroids and Prions 1

Topics: Virus, DNA, Bacteria Pages: 24 (1483 words) Published: February 10, 2015
Viruses, Viroids,
and Prions
copyright cmassengale

1

Are Viruses Living or
Non-living?
Viruses are both and neither
They have some properties
of life but not others
For example, viruses can be
killed, even crystallized like
table salt
However, they can’t
maintain a constant internal
state (homeostasis).
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2

What are
Viruses?
A virus is a noncellular particle
made up of genetic
material and
protein that can
invade living cells.

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3

Viral
History
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4

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
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5

Tobacco Mosaic Virus
Wendell Stanley
(1935) crystallized
sap from sick
tobacco plants
He discovered
viruses were
made of nucleic
acid and protein
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6

Smallpox
Edward Jenner
(1796) developed a
smallpox vaccine
using milder cowpox
viruses
Deadly viruses are
said to be virulent
Smallpox has
been eradicated in
the world today
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7

Viewing Viruses
Viruses are
smaller than the
smallest cell
Measured in
nanometers
Viruses couldn’t
be seen until the
electron microscope
was invented in the
20th century
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8

Size of Viruses

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9

Viral
Structure
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10

Characteristics
Non living structures
Noncellular
Contain a protein coat called
the capsid
Have a nucleic acid core
containing DNA or RNA
Capable of reproducing only
when inside a HOST cell
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11

Characteristics
Some viruses are
enclosed in an
protective envelope
Some viruses may
have spikes to help
attach to the host
cell
Most viruses infect
only SPECIFIC host
cells
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CAPSID
DNA

ENVELOPE

SPIKE
S
12

Characteristics
Viral capsids
(coats) are
made of
individual
protein subunits
Individual
subunits are
called
capsomeres
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CAPSOMERES

13

Characteristics
Outside of host cells,
viruses are inactive
Lack ribosomes and
enzymes needed for
metabolism
Use the raw
materials and enzymes
of the host cell to be
able to reproduce

EBOLA VIRUS

HIV VIRUS
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14

Characteristics
Some viruses cause
disease
Smallpox, measles,
mononucleosis, influenza,
colds, warts, AIDS, Ebola
Some viruses may
cause some cancers like
leukemia
Virus-free cells are rare
MEASLES
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15

Viral Shapes
Viruses come in a variety
of shapes
Some may be helical shape
like the Ebola virus
Some may be polyhedral
shapes like the influenza
virus
Others have more complex
shapes like bacteriophages
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16

Helical Viruses

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17

Polyhedral Viruses

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18

Complex Viruses

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19

Taxonomy of
Viruses

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20

Viral Taxonomy
Family names end in -viridae
Genus names end in -virus
Viral species: A group of viruses
sharing the same genetic information
and ecological niche (host).
Common names are used for
species
Subspecies are designated by a
number
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21

Viral Taxonomy
Examples
Herpesviridae
Herpesvirus
Human herpes virus 1, HHV 2, HHV 3

Retroviridae
Lentivirus
Human Immunodeficiency Virus 1, HIV 2
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22

Herpes Virus

SIMPLEX I and II

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23

Adenovirus

COMMON COLD
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24

Influenza Virus

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25

Chickenpox Virus

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26

Papillomavirus –
Warts!

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27

Used for Virus
Identification
RNA or DNA Virus
Do or do NOT have an
envelope
Capsid shape
HOST they infect

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