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Chapter 24 Viruses
Section 1 Vocabulary Pretest
Virus
Retrovirus
Capsid
Reverse transcriptase
Envelope
Bacteriophage
Provirus
Lytic cycle
Virulent
Lysis
Lysogenic cycle
Temperate virus
Prophage
Discovery of Viruses
• ______________: Nonliving particle made up of ___________________________
and a _______________________ (or lipid-protein coat)
• ________________________ in living organisms
• Useful tools for __________________________
• Very ______________ (need electron microscope to see)
• Can be ____________________
Characteristics of Viruses
• Lack ____________________ and _____________________________
• Cannot carry out the ____________________________ of metabolism,
homeostasis, respiration or photosynthesis
• Can only reproduce ____________________________ by utilizing the host cell’s
ribosomes, ATP, enzymes and proteins.
Size and Structure
• Viruses _________ in size and shape
• Most are surrounded by a protein coat known as a __________. Capsid shapes
include:________________________________
Bacteriophages
• The _______________ viruses are those that infect ________________________.
• They are called _____________________.
• They have a _________________________.
Enveloped Viruses
• Some viruses have a _______________________ called an __________________
that surrounds the capsid.
• It forms from the _____________________________ as the virus buds out from the
host.
• Ex: __________________________________________
• The proteins on the envelope help the virus ______________________________.
Classification of Viruses
• Most viruses are classified according to the type of nucleic acid they contain:
______________________
Viral Replication
• Viruses are ___________________________________ —they replicate only by using
host cell enzymes and organelles to make more viruses.
Replication in DNA viruses
Replication in RNA Viruses
• The genome of RNA viruses serves as a template for the _______________________
which is then translated to make viral proteins and as a template for ____________
_____________________________________________Retroviruses
• ___________________________ are RNA viruses that also contain the enzyme
________________________________
• This enzyme uses RNA as a template to ____________________.
DNA): hence the name
• The flow of information is ___________________ (RNA
“retro” virus.
• ___________ is a retrovirus.
• The viral DNA that is copied by reverse transcriptase is then _________________
into the host genome and becomes a _____________________.
• The provirus remains a ________________________________ of the host cell.
• The host’s enzymes _________________ the proviral DNA into _________________
that function both as _________ to make viral proteins and as _________________
for new viruses.
Viral Replication in Prokaryotes
• Viruses that infect prokaryotes are called ____________________, or __________.
• __________________________
• Replicate using either the _______________ or the ________________________.
Lytic Cycle
• Viruses that use the _______________ are called _________________________.
• Infection results in an immediate _________________________________________
and the complete destruction (_____________) of the host cell.
Lysogenic Cycle
• Viruses that use the ___________________are called ________________________.
• After infection, these viruses can ______________________ in their host cell for
days, months, or years.
• The viral genome ___________________________ into the bacteria’s DNA
chromosome. It is now called a __________________.
• Unlike proviruses, which are permanently integrated, a prophage can
_________________________________and then enter the ___________________.
Viruses: tools for Biotechnology
• Phage viruses have become very useful in __________________________________
• Phage DNA is ________________ with DNA of interest (ex: human gene for insulin)
• Phage is allowed to ____________________________.
• Bacteria then produce large amounts of either ___________ or copies of the
_____________________.
Origin of Viruses
• It is believed that viruses ____________________________________ (since they
cannot reproduce without cells)
• They were probably tiny pieces of naked nucleic acid that could ______________
___________________________.
• _________________________________ evolved on a few mutant pieces of DNA and
….the first virus evolved.
• Many viruses ____________________ (especially RNA viruses). This makes it
difficult for the immune system to recognize them as well as to develop vaccines to
fight them.
Section 2 Vocabulary Pretest
Vector
Proto-oncogene
Protease inhibitor
Emerging disease
Oncogene
Inactivated virus
Attenuated virus
Viroid
Prion
Viral Diseases
• Most viruses must be spread by an intermediate host known as a _______________.
• Vectors can include: ______________________________________________.
Human Viral diseases
• _______________________________
• Caused by the ________________________________.
• Multiplies in the ___________ and travels to ___________________________
causing ______________ and ____________________
• Spread through __________________ with the skin rash and through the air
• If the virus stays as a _____________ in _________________, it can later
cause ______________
• __________________________
• Hepatitis: _________________________; causing fever, nausea, jaundice and
liver failure
• _________ viruses can cause it:
• __________________ —spread by fecally contaminated food and water
• __________________ —spread by sexual contact; and blood to blood
contact (contaminated needles)
• ________________________________________________
• Caused by __________________ (human immunodeficiency virus)
• Destroys _______________________
• Spread by _____________________ (contact with infected body fluids: blood,
semen, vaginal fluid; and from mother to fetus)
• ____________________ that can infect ____________ of the immune system
• It will __________ many of the T cells. Others, it will infect and stay hidden as
a ____________________ to avoid detection.
• Efforts to fight AIDS have focused on drugs that _________________________
__________________________________
• ___________ inhibits the ability of reverse transcriptase to make a DNA
copy of the viral RNA.
• _______________________ block the synthesis of new viral capsids.
• Most effective treatments involve a _____________________________
____________ (AIDS cocktail)
• With treatment, many people have manage to _____________________
______________________________________
Viruses and Cancer
• _______________: results from cells that ____________________________
• Some viruses can cause cancer because they contain _________________: genes
that _______________________________________________.
• Other viruses cause cancer because they ___________________________________
________________________ which normally controls cell growth. They disrupt the
function of this portion of DNA.
• Cancers caused by viruses include: ______________________ (caused by HPV:
human papillomavirus); _____________________ (caused by Hepatitis B);
________________ (caused ______________________________ Burkitt’s
lymphoma (caused by Epstein-Barr virus)
Emerging Viral Diseases
• _________________________: illnesses caused by new or reappearing infectious
agents that typically exist in animal populations—often in isolated habitats—and can
infect humans who interact with these animals.
• _______________________________________
• Fatal pneumonia caused by _________________
• ______________
Prevention and Treatment
• ____________________ DO NOT work on viruses. Your immune system is your main
defense after you have been infected.
• ___________________: a harmless version of the virus is injected in order to
_______________________________. These are used to ___________________
_______________…not cure them. They make use of:
• ______________________: cannot replicate
• ______________________: weakened form that cannot cause disease
• Successful vaccines exist for: ___________________________________________
_____________________________
• ________________ has been eradicated using a worldwide vaccine campaign
carried out by the ______________________________
• Last known case of smallpox was in ________________________
• Declared ____________________ in 1980
• _______________________: involves controlling the animal vectors used by viruses.
• Ex: __________________________ help stop the spread of yellow fever:
_____________________________ of pets help stop the spread of rabies.
• __________________: this approach is limited to drugs that interfere with viral
replication inside cells.
• ________________ blocks DNA polymerase of herpes viruses and chickenpox
virus. They do not destroy the virus.
Viroids and Prions
• ______________: smallest known particles that can replicate
• Short strand of ___________: no capsid
• Infect plants: such as coconuts, potatoes and oranges
• ______________: infections proteins.
• Cause _____________________________________________________