Download What are Viruses

Viruses
Introduction
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A virus is a tiny nonliving particle that enters
and then reproduces inside a living cell.
Some of the organisms Viruses infect include:
1. Humans
2. Plants
3. Animals
4. Bacteria

What do you call a Virus that infects bacteria?
Bacteriophage which means “bacteria eater”
Viruses
Introduction

What is an Infection?
When bacteria or viruses cause a disease or
an illness
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The virus is called a parasite. Parasite can
only live in a host
What is a host?
An organism that provides energy and a
suitable environment/home for a parasite
How big are they?

What size is the
bacterium ?
750nm
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What size is the Red
Blood Cell?
7,500nm
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What size is the
influenza virus?
90nm
The Structure of
Viruses
1. A protein coat
that protects
the virus called
Capsid
All viruses have two basic parts
2. An inner core
made of genetic
material DNA
or RNA
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Some viruses
are surrounded
by an Membrane
envelope.
DNA and RNA viruses
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T4 bacteriophage is
a DNA virus
Magnification:
x55,065
Some viruses have
RNA instead of DNA
HIV is type of RNA
virus
How do viruses attach
to a Host cell?
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Viruses have outer
membrane proteins
The host cell
membrane also has
proteins on it
The host and the virus
surface proteins fit
together like a
“LOCK AND KEY”

If these do not fit
together the virus will
not be able to attach
to the host cell and
infect it !
Bacteriophage
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Virus that infects only
bacteria
The DNA is inside the head
The head is made of special
protein coat called:CAPSID
The tail contracts and pushes
the DNA inside the bacteria
The fibers have special
Binding proteins that attach
to bacterial cell wall
Bacteriophage

The head passes its DNA
down the tail and into the
host (bacteria)

Within 25 minutes the dying
bacteria is teeming with
about 100 fresh copies of
the virus

Viruses use the bacteria’s
machinery such as the
Ribosomes to make proteins
needed to assemble new
viruses
How Active Viruses Multiply
ACTIVE VIRUSES enter cells and immediately begin to multiply,
which may lead to the quick death of the invaded cells.
Active viruses cause ACUTE INFECTION which only last few days
How Active Viruses Multiply
Virus attaches to the surface of a living cell.
Virus injects genetic material into cell.
Cell produces viral proteins and genetic material.
Viruses assemble.
Cell bursts, releasing viruses.
How Hidden Viruses Multiply
HIDDEN VIRUSES “hide” inside host cell before becoming
active. Hidden viruses cause CHRONIC INFECTION which
can last a lifetime
How Hidden Viruses Multiply
Virus attaches to cell.
Virus injects its genetic material.
Virus’s genetic material becomes part of cell’s genetic
material.
Cell produces viral proteins and genetic material.
Viruses are assembled
Cell bursts, releasing viruses.
Review Questions
Question:
Answer:
What kind of organisms do viruses infect?
Humans Animals Bacteria Plants
Question:
Answer:
Explain the difference between a host and a parasite
* Host is the infected organism, provides suitable home
for the parasite
* Parasite needs a host to live
Question:
Answer:
What is the name of a virus that infects only Bacteria?
A Bacteriophage or T4 phage
Question:
Answer:
Name the basic parts of a virus
* Protein coat called “Capsid”
* DNA or RNA
* Some viruses have an “outer membrane”
Question:
Answer:
What type of genetic material is inside a virus?
Either DNA or RNA but not both
Question:
Answer:
Briefly describe what is an “Active Virus” ?
* Active virus infects a host and multiplies
immediately
* Causes “Acute Infection”
* Example: the Flu
Question:
Answer:
Question:
Answer:
Briefly describe what is a “Hidden Virus”?
* Infects a host but doesn’t multiply immediately
* Causes “Chronic Infection”
* May last a lifetime
* Example: The HIV that causes AIDS
Herpes
Epstein-Barr
How do viruses attach to a host cell?
Both the host and virus have special proteins that fit
together like a “Lock and Key”