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Doesn’t belong to any kingdom
-It’s not a plant or an animal.
-It’s not a fungi, protist, or
bacteria.
WHAT IS A VIRUS?
What is a Virus?
1) A virus is an infectious
agent made up of nucleic
acid (DNA or RNA) wrapped
in a protein coat called a
capsid.
Some viruses have an
envelope, a lipid bilayer
(=membrane w/ two layers)
that surrounds the capsid.
Are Viruses Cells?
2) Viruses have no nucleus, no organelles, no
cytoplasm or cell membrane. They are NOT cells.
-This is why they do not belong to any kingdom.
vs.
Are Viruses Living?
3)
Criteria
Yes
Kind of
√
Reproduce
√
Energy Use
Adapt
No
√
Cells
√
Homeostasis
√
Nucleic Acids
(must have
both)
Growth
Organization
√
√
√
Are Viruses Living?
4) Are they considered living?
No, they would have to meet
all 8 qualifications to be
considered alive.
5) Even though viruses do
have genetic material
(DNA or RNA) and it can
change (adapt), they
cannot reproduce on their
own, they’re not cells,
they cannot maintain
homeostasis, they do not
grow (rather, they’re
“assembled”), and they do
not have organization.
Classification of Viruses
6) Viruses can be classified based
on:
a. Nucleic Acid type (DNA/RNA)
b. Shape of Nucleic Acid
7)
c. Shape of Capsid
d. Presence of Envelope
Hosts
8) Viruses are like parasites—they depend entirely
upon another living organism (= a host) for its
existence in such a way that it harms that organism.
9) Bacteriophage—viruses that infect bacteria
Capsid (protein coat)
– inside contains either
RNA or DNA
10) Influenza and HIV,
for example, infects
human cells.
DNA or RNA
Surface
Marker
Capsid (protein coat)
Viral Replication
11) Viral Replication is how a virus makes copies of itself.
A virus CANNOT reproduce by itself—it must invade a host cell and take over
the cell’s “machinery”, make copies of itself, and eventually will cause the
cell to burst (lyses), releasing more viruses. This kills the host cell.
Virus attaches
to cell.
Step 3
Step 2
Step 1
Virus copies
itself.
Step 4
DNA/RNA is
copied.
DNA/RNA injected
into cell.
Cell bursts (lyses) and
releases new viruses.
Step 5
Viral Transmission
12) Outside the host
cell, a virus is a lifeless
particle with no
control over its
movements. It is
spread by:
•Air
•In water
•In food
•By body fluids
Viruses as Pathogens
13) Many viruses cause disease
= pathogenic
-Pathogen = disease-causing
agent (could be a bacterium, protist, fungus)
14) Human diseases caused by
viruses: Warts, common cold,
Influenza (flu), Smallpox, Ebola,
Herpes, AIDS, Chickenpox, Rabies
15) Some viruses can be prevented
with vaccines, but NOT treated with
antibiotics (antibiotics treat
bacteria).
Benefit of Viruses
16) Genetic Engineering—harmless virus carries
good genes into cells.