Viruses are non-living intracellular parasites that cannot be cultivated in cell-free media. Where must they be grown?
Must be grown in tissue culture, frequently grown in embryonated bird eggs
Viruses are Small in size, largest is about
A single virus particle is referred to as a
Genome is either?
RNA OR DNA, but not both
Nucleic acid is enclosed in?
protein coat called a capsid (nucleic acid + capsid = nucleocapsid)
Some viruses have lipoprotein envelope, from where?
acquired from host cell
Envelope has what features?
glycoprotein spikes for interaction with host cell
Viruses with a capsid, but no envelope are called
Two primary types of symmetry of capsid
Viruses have different shapes, name the three
spherical, bullet shaped, or filamentous
Agents with no detectable nucleic acid
Appears to be self-replicating protein
Some scientists believe a relationship to viruses exists
Responsible for the neurodegenerative diseases classified as spongiform encephalopathies (SE). Diseases cause holes in tissue, brain appears as a sponge
SEs include mad-cow disease, Creutzfeldt-Jacob, Kuru, scrapie
Much of our understanding of How Viruses Replicate and Multiply comes from?
studying bacteriophages (bacterial viruses)
The Lytic Cycle of Bacteriophages: Adsorption – is defined as what?
bacteriophage irreversibly adsorbs to receptor site using tail fibers
The Lytic Cycle of Bacteriophages: Adsorption –Various receptor sites include?
Lipopolysaccharide of Gram neg. cells
Pili and flagella
Beginning of latent period- latent period continues until cell lyses: When does this begin?
The Lytic Cycle of Bacteriophages: Adsorption
The Lytic Cycle of Bacteriophages: Penetration – is defined as what?
phage tail penetrates bacterial cell, nucleic acid enters leaving capsid on outside of host cell
The Lytic Cycle of Bacteriophages: Penetration, Beginning of eclipse period – Define it?
defined as period during which no viral particles can be found either inside or outside cell, viral DNA is taking over machinery of host cell
What occurs during the The Lytic Cycle of Bacteriophages: Penetration: Eclipse Period?(2)
First mRNA is transcribed to code for a repressor enzyme to prevent entry of other phages
Second additional enzymes are produced to depolymerize host cell DNA.
Destruction of host cell DNA leads to?(4)
Halt of host cell metabolism
Virus assuming control of host cell metabolism
Viral nucleic acid being assembled using host nucleotides
Use of host cell ribosomes for translation of viral mRNA
The Lytic Cycle of Bacteriophages: Prefabrication, What occurs?(3)
Viral genome is replicated multiple times
Necessary viral mRNA is synthesized
All viral parts are “prefabricated”
The Lytic Cycle of Bacteriophages: Maturation, What occurs?(3)
End of the eclipse period
New viruses are assembled
Viruses DO NOT grow, cells grow, viruses are assembled
The Lytic Cycle of Bacteriophages: Viral release, What occurs?(4)
End of latent period
New viruses produce lysozyme
Lysozyme causes the bacterial cell wall to rupture
Viruses are released
ANIMAL VIRUSES - Adsorption, What Occurs?
Host cell receptors are normal surface molecules involved in routine cellular function
Naked virus – capsid proteins bind to host cell receptors
Enveloped virus – glycoprotein spikes bind to host cell receptors
ANIMAL VIRUSES - Penetration and uncoating, what occurs with Naked Viruses?
Naked viruses undergo a major change in capsid structure on adsorption to plasma membrane, so that their nucleic acids are released into the cytoplasm
ANIMAL VIRUSES - Penetration and uncoating, what occurs with Enveloped Viruses?
Enveloped viruses enter the host cell in one of two ways
viral envelope may fuse with the host cell cytoplasmic membrane and the nucleocapsid is released into the cytoplasm
animal viruses enter by endocytosis whereby the host cell cytoplasmic membrane invaginates and pinches off, placing the virus in an endocytic vesicle. Lysosomes fuse with vesicle and uncoat releasing nucleic acid
ANIMAL VIRUSES - Synthesis (Replication) DNA Viruses, give the rundown.
Early synthesis = host cell is overtaken- viral DNA is synthesized and transcribed to RNA, inhibit host cell DNA, RNA and protein synthesis
Viral DNA replication usually occurs in host nucleus (exception = poxviruses are replicated in the cytoplasm)
DNA viruses often remain latent in the infected cell
Early viral genes transcribe DNA binding proteins and enzymes
Late viral genes transcribe structural proteins
ANIMAL VIRUSES - Synthesis (Replication) RNA Viruses: Name the Four Groups of RNA
Synthesize mRNA and replicate RNA genome by converting RNA to DNA
Reverse transcriptase converts (+) RNA to (-) DNA
The (-) DNA is copied to create a double stranded DNA called proviral DNA
Proviral DNA synthesizes (+) RNA genome for new viruses
ANIMAL VIRUSES - Maturation - Assembly of new viruses - Capsid formation, How is it done?
Capsid protein synthesis is directed by late genes (structural)
Spontaneously self-assemble- capsid around nucleic acid
Location of maturation is virus specific
ANIMAL VIRUSES - Maturation - Assembly of new viruses - If Enveloped: How is it done?
Late viral mRNA transcribes glycoproteins
Glycoproteins are inserted into the host cell membrane
Virus particle acquires the glycoprotein envelope during exocytosis
ANIMAL VIRUSES - Viral release - Naked virus, how is it done?
infected cell usually lyses and the virions are released
ANIMAL VIRUSES - Viral release - Enveloped virus, how is it done?
The host cell may or may not be lysed
Virus obtains its envelope by budding from membrane bound organelles within the cell
Transport vesicles carry the virus to the cell surface where it is released by exocytosis
persistent infections are those in which the virus is not cleared from the host following primary infection, but remains associated with specific cells
some DNA viruses and retroviruses establish persistent infections that stimulate uncontrolled cell growth causing transformation or immortalization of the cell (cancer cells)
Define Immunological escape
many viruses have evolved systems of immunological escape to evade detection ie herpes viruses escape detection by integration into host cell DNA
Describe DNA Poxviruses
Large brick shaped viruses – largest of all viruses, 200 nm
Virions contain one molecule of linear double stranded DNA
Name the five DNA Pox Viruses
Describe Molluscum contagiosum
Small pearly or flesh-colored bumps
Contagious but is not harmful
In people with impaired immune systems bumps can be extensive and disfiguring
Disease caused by variola virus
Variola major- the more severe form
Variola minor- more mild form
Highly contagious, respiratory secretions and direct contact transmission
Fever, chills, nausea, severe muscle aches
Rash begins as flat lesions, progress to papules- eruptive stage
Papules become pustules, scab, leave scar
In 1967, the WHO undertook a global program of smallpox vaccination. At that time, 10 to 15 million cases of the disease occurred each year, with more than 2 million deaths
The last case of endemic smallpox was reported in Somalia in 1977
Considered eradicated in 1980
Describe Cow pox
Causes human disease through zoonosis
Transmission to humans traditionally occurred via contact with the infected teats of milking cows
Vaccinia virus is a big mystery in virology. It is not known whether vaccinia virus is the product of genetic recombination, or if it is a species derived from cowpox virus or variola virus by prolonged serial passage, or if it is the living representative of a now extinct virus.
Vaccinia virus was used for smallpox vaccination
Describe Monkey pox
Rare viral disease found mostly in the rain forest in west Africa.
Called “monkeypox” because it was first discovered in laboratory monkeys in 1958
Orf is a viral pox infection of the skin contracted from sheep and goats
Describe Herpes Viruses
A leading cause of human viral disease, second only to influenza and cold viruses
Once a patient has become infected by herpes virus, the infection remains for life
Single molecule of double stranded DNA
Attracted to neurons
Name the 7 Herpes Viruses
Varicella- Zoster Virus (VZV)
Herpes simplex viruses (HSV)
Epstein Barr (EBV)
Human herpes virus 6
Human herpes virus 7
Human herpes virus 8
Decribe Cytomegalovirus (CMV)
By college age, about 15% of the US population is infected and this rises to about half by 35 years of age.
The virus is spread in most bodily secretions
Cytomegalovirus infection is therefore sexually transmitted
Transplacental infection - CMV can also spread to a fetus in a pregnant woman
Most common viral cause of congenital disease (mental retardation)
Up to one in forty newborns in the U.S. are infected by the virus
CMV causes no symptoms in children and at most mild disease in adults
CMV can be a major problem for those who are immunosuppressed
CMV in AIDS Patients Causes what?
Particularly important is CMV-retinitis in the eye which occurs in up to 15% of all AIDS patients
Varicella- Zoster Virus (VZV) is also known as what?
Also known as human herpes virus-3
Varicella- Zoster Virus (VZV) causes what two diseases?
VZV causes two diseases, chicken-pox, usually in childhood, and shingles, later in life