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Viruses Chapter 24
In the late 1800’s
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Scientists really didn’t know _________ about what a virus was (no tech)
They found out that it __________ a bacteria causing the disease.
They knew it was _____________ than a bacteria cell
Scientists began to study _____________
They wanted to know if they were __________________ or not
So are Viruses made of cells?
Wendell Stanley 1935
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He took a TMV ( __________________________________) plant and broke it down to
it’s _________________ part
He was expecting to see a cell, but instead he saw _______________
So Wendell concluded that viruses are ______ alive!
Characteristics of Viruses
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Lack __________________
Lack __________________
Cannot do ____________________
Cannot do ____________________
Do not have ___________
Have _______________, not both
Cannot ________________ outside their _______ cell
o They must __________ a living cell and use it’s machinery (ribosomes, ATP
& enzymes) in order to reproduce
Viral Sizes
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Extremely small; _____________ be seen using a light microscope
________ in size and shape
__________________
________________
________________
Virus Structure
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___________ - protein coat that surrounds it’s DNA or RNA
___________ - some viruses have this 2nd layer. It is made of specific proteins and
help new viruses recognize host cells (ex. – chickenpox & HIV)
____________________ - (viruses that attack bacteria) have a tail and tail fibers
STEM 2011
Characteristics of Viruses
Viruses can be classified based on:
 whether they have ______________
 whether the RNA or DNA is __________ or double stranded
 Whether the RNA or DNA is _____________ or linear
 capsid _________
 whether or not they have an _____________
Other things….
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Outside their host, virus’s are lifeless with _______________over its movements
Viruses are spread through
In order to replicate, viruses need to ________________ the appropriate host cell
before it can infect it. An enveloped virus needs to match the host cell’s
membrane receptors precisely.
Replication in DNA Viruses
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The DNA in some DNA viruses enter a host cell and then it makes _________
The DNA in some DNA viruses insert into the host’s chromosomes. Then it is called
a _______________
Some DNA viruses use the host cell enzymes to make new viral DNA and
eventually _________ viruses!
STEM 2011
Replication in RNA Viruses
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Some RNA viruses enter their host and that RNA serves as ________, which then is
translated into new viral proteins immediately
Some RNA viruses, called __________________ contain the enzyme _____________
________________ in addition to RNA.
o Reverse transcriptase uses RNA as a _____________ to make DNA, which
then inserts into the host cell’s genome.
o Reverse transcriptase _________________ the normal process of
________________
o ______ is a retrovirus
Replication in Bacteriophages
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Remember bacteriophages are viruses that _____________bacteria
They have_____________ capsids
They replicate by one of both of two different methods:
_____________ cycle
_______________ cycle
Lytic Cycle
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Lytic = ___________ = _____________
o This means that the host cell will rupture after replication is
completed.
Viruses that do this cycle are called _______________
There are ___ steps to the lytic cycle
5 Steps to the Lytic Cycle
1. ________________ attaches its tail fibers to specific receptor molecules on
the cell ____________ of a bacteria cell. The _______________ into the host
cell
2. The ends of the viral DNA attach to each other, forming a ___________. It is
________________ from the host cell’s DNA
3. The viral DNA takes control of ______________________ and the viral
genome is __________. Enzymes and ribosomes are used from the host
cell.
4. ________________________ are made and put together
5. ________________ enzymes digest the cell wall and up to _____ new viruses
are released.
STEM 2011
Lysogenic Cycle
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Host cell does _____ get killed
It allows viruses to ______ in the host cell for days, months or even years.
A virus that does this cycle is called ______________
5 steps
5 Steps to Lysogenic Cycle
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Bacteriophage attaches to host cell and _____________ it’s DNA
Viral DNA attaches its ends to make a circle
The viral DNA then ______________ into the host DNA – now it’s a ______________
When the bacteria ______________ it’s own DNA, it replicates the viral DNA. So
now each bacteria cell will be infected with a prophage.
5. The prophage will _________ the host cell – usually caused by radiation or
_____________
STEM 2011
The Origin of Viruses
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Most scientists think viruses originated from __________ pieces of nucleic acid and
evolved from that
Viruses ____________ quickly, such as influenza and HIV
It is difficult for the________________ to recognize and destroy them, which makes
it hard to make good vaccines.
A ___________ is a ______ virus that is injected so that the body can make
________________ to kill it
Therefore each year, there is a new ______________ available,
Vectors of Viral Diseases
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_______________, or hosts, of viral diseases include humans, animals, and insects.
They _____________ a pathogen or parasite or virus to another organism
Human Viral Diseases
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Viruses cause _________ human diseases, including the common cold, flu,
hepatitis, rabies, chickenpox, certain types of cancer, and AIDS.
They can affect various human __________, such as the brain, liver, heart, lungs
and skin
Chickenpox and Shingles
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Chickenpox and shingles are caused by the ________ varicella-zoster
herpesvirus.
It multiplies in the _________ and travels to blood vessels in the __________
Symptoms are fever and _______________
It is spread thru _________________ with the skin rash and through the air
After having it, people usually won’t get it again, but it can stay in the nerve cells
are a ______________. Then if it gets activated, it’s called ________________.
Viral Hepatitis
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Hepatitis, or inflammation of the _________, can be caused by at least five viruses.
Hepatitis ___ and hepatitis ___ can be spread by ___________ contaminated food
and water.
Hepatitis ___, ___, and ___ are spread by _________________, by contact with
infected __________ and serum,and by the use of contaminated _____________.
Symptoms are fever, nausea, _______________ & liver failure
Acquired Immune Deficiency Syndrome (AIDS)
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The human immunodeficiency virus (HIV) is an _______________ spread by sexual
contact, by contact with infected body fluids, and from ______________________.
HIV targets _________________, which are immune system cell, and thus damages
the body’s immune system. The disease called acquired immune deficiency
syndrome (AIDS) results.
STEM 2011
HIV
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Virus attaches to the CD4 and CCR5 ______________ on cell surface. Binding must
occur.
The viral envelope __________ with the membrane and releases the ___________
into the host cell
Viral RNA and reverse transcriptase are released and used to make a template
to make a double stranded ______ version of the viral genome
The HIV DNA enters the cell’s nucleus and integrates into the cell’s DNA, thus
making a ______________
Transcription and translation occurs and __________________are made
Then HIV ______________ and a new envelope forms around it and eventually is
released from the cell
AIDS (Acquired Immunodeficiency Syndrome)
Viruses and Cancer
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Some viruses contain ________________ that can cause cancer
other viruses convert ____________________, which usually control cell growth, to
oncogenes.
Human papillomavirus (HPV) can cause __________________ and hepatitis B virus
can cause ___________ cancer
STEM 2011
Emerging Viral Diseases
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________________________ usually infect animals ________________ in nature but
can jump to humans when contact occurs in the environment.
_________________ – animals in tropical forests of central Africa
__________ – civet cats
Vaccines are ________________ to develop for these infectious diseases
Prevention and Treatment
Vaccinations
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A vaccine contains a _______________ version of a virus, bacterium, or a
toxin that causes an immune response when introduced to the body.
Vaccines have helped to greatly reduce certain viral diseases.
Viral vaccines are made from _____________________, which are viruses
that are unable to replicate in a host
Attenuated Viruses
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________________ forms of a virus that cannot cause a disease
When made into a vaccine, they provide ___________ protection from disease
Ex., measles, ___________, rubella, polio, hepatitis a and b and chicken pox
Viroids and Prions
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_____________ are short, circular, single strands of RNA lacking a capsid that
infect plant cells.
______________are infectious particles containing protein but no nucleic acids.
Prions cause _____________________ and similar degenerative brain diseases.
Important Viral Diseases
STEM 2011