Chapter 6: Viruses Flashcards
Viruses characteristics
- considered particles
- are not alive
- ultra microscopic
- DNA/RNA allows them to reproduce
what does the term virus mean in Latin?
poison
who coined the word for virus
L. Pasteur
what do viruses have in common with cells?
the presence of nucleic acids
what type of microscope is necessary to observe viruses?
electron microscope
- they are measured in nanometers
what is a capsid
- a layer of protein acting as a shell surrounding the virus’ genetic material
what is an intracellular parasite
can only reproduce inside the cell
What is the largest virus?
poxviruses; size of small bacteria
How many genes does the Hepatitis B virus have?
4
what is the smallest virus?
parvovirus
what is Reverse Transcriptase and what is an example of a virus with such feature?
an enzyme present in some RNA viruses that allows the mRNA to be converted back to DNA
ex. Retrovirus
- this does not happen in regular biology
when is a virus considered a naked virus?
it only consists of a capsid
when is a virus classified as an enveloped virus?
virus has extra layer of phospholipids (envelope) in addition to the capsid
what are spikes and their function?
aka peplomers
- made of a glycoprotein
- function is to recognize a receptor to bind to a cell to reproduce
- acts as a key finding a lock
examples of complex viruses
- bacteriophages: viruses that affect bacteria
- T4 virus (looks like a spacecraft)
- poxviruses
what are the different type of viral morphology?
- naked
- enveloped
- complex
what is the genome?
sum of all genetic information carried by an organism or virus
describe the genome of a virus
consists of only the necessary enzymes to cause infection
ex. T4 has a special enzyme that, when attached, opens a hole in a cell to inject its DNA into the host cell
what kind of genetic material does a virus have?
DNA or RNA, but not both
- single stranded DNA
- double stranded DNA
- double stranded RNA
- single stranded RNA
examples of single stranded DNA viruses
- parvovirus: kills puppies
- geminivirus: in agriculture
what is meant by linear non fragmented
genome is organized in a continuous sequence, round or linear when stretched
what is meant as linear fragmented
ex. flu virus has 8 pieces of RNA
ex. reovirus has 11 pieces of RNA
example of double stranded RNA
- reoviridae
»>rotavirus: causes diarrhea in children
which DNA virus has both double and single stranded portions of DNA?
Hepatitis B
- considered a defective virus
how many virus families affect humans?
19
- 6 DNA
- 13 RNA
what committee is responsible for the taxonomy of viruses?
International Committee of Taxonomy of Viruses (ICTV)
what is the total number of families of viruses
63
how are virus families termed
-viridae
how many genera of viruses are there?
263
how are virus genera termed?
-virus
how does the ICTV recommend for the writing of the order, family, and genera
they should italicized
what are the six DNA viruses affecting humans?
- herpesviridae
- poxviridae
- papoviridae
- hepadnaviridae
- parvoviridae
what are the 4 genera of herpesviridae and what do they cause?
- HSV Type I
- herpes
- hides in the nerves - HSV Type II
- genital herpes - Epstein-Barr (EBV)
- mononucleosis
- affects young people
- transmitted through kissing - Varicella-Zoster (VZR)
- rash
what two diseases does Varicella-Zoster (VZR) cause and what time frame?
Varicella (chickenpox) is acquired when an individual is young. The virus hides in the nerves until it manifests into Zoster (shingles) when person is older.
what does the term herpes mean in greek?
to creep; appearance of blister looks like a snake creeping up on the nerve
what are 2 genera included in poxviridae?
- smallpox
- cowpox
what type of virus is herpesviridae?
enveloped virus
what type of virus is poxviridae?
complex virus
Poxviridae includes all “pox” virus genera EXCEPT:
chicken pox; it is part of herpesviridae
What genera does adenoviridae include?
adenovirus
what is the morphology of adenovirus?
looks like a satellite
adenoviridae characteristics
- affects children
- can cause conjunctivitis (pink eye)
- affects adenoids (tonsils)
papoviridae characteristics
- causes warts
- genus Human Papillomavirus consists of a lot of viruses that causes warts
- they can then lead to cervical
cancer (HPV)
hepadnaviridae characteristics
- hepa = liver
- hepatitis B virus has four genes and it can kill you
- not considered an STD - has double and single stranded DNA
parvoviridae characteristics
- parvo = very small
- only one genus can affect humans which is parvovirus B-19 (erythema infectiosum)
- ALSO affects puppies :(
what are the 13 virus families affecting humans?
Picornaviridae genera (4)
- pico = small
1. poliovirus
2. Coxsackievirus (hand-foot-mouth disease)
3. Hepatitis A virus (short-term hepatitis)
4. rhinovirus (common cold, bronchitis)
Calicivirus
- calici = food in greek
- Norwalk virus aka norovirus
- number one virus affecting food
- causes explosive diarrhea
- spreads quickly
togaviridae has what 4 genera
- eastern equine encephalitis virus
- western equine encephalitis virus
- rubella virus
- St. Louis encephalitis virus
Flaviviridae and its 5 genera
- flavi = yellow
1. Dengue fever virus
2. West Nile virus
3. Yellow fever virus
4. Hepatitis C virus
5. Zika virus - fetus can be born with small skull
how are flaviviridae viruses spread
- through arthropods like mosquitos, except for Hepatitis C
- can only be transmitted from person to person through blood transfusion
Bunyaviridae (5 genera)
- Crimean-Congo hemorrhagic fever virus
- causes bleeding from eyes, ears, nose, etc. till you death - Rift Valley fever virus
- Sin Nombre virus
- Bunyamwera virus (California encephalitis)
- Hantavirus (Korean hemorrhagic fever)
Why is it named Filoviridae? (2 genera)
- filo = little filament
- virus looks like a little filament
1. Ebola virus - found in Africa
2. Marburg virus
Reoviridae (2 genera)
- has 11 segments of RNA
1. Rotavirus (gastroenteritis) - common in the RGV; causes diarrhea in children
2. Colorado tick river virus
What genera is included in the Orthomyxoviridae family?
includes Influenza virus
- has 7-8 fragments
- causes flu
Paramyxoviridae (4 genera)
- Mumps virus (mumps)
- Parainfluenza virus (parainfluenza)
- Measles virus (measles)
- Respiratory syncytial virus (common cold syndrome)
Why is it named Rhabdoviridae what is its genera?
- rhabdo means short in greek
- looks like a bullet
1. Lyssavirus (rabies virus) - nobody will survive
What is unique about Retroviridae and is its 2 genera?
- have reverse transcriptase (only found in this family)
1. Lentivirus - HIV, types1 and 2, cause AIDS
2. Human T-cell leukemia virus (HTLV)
Why the name Arenaviridae and what is the one genera?
- “Arena” means sand; biologists saw a lot of granules under the microscope that resembled sand. They were ribosomes.
1. Lassa virus - causes lassa fever
- found mostly in Africa
- round with spikes
Coronaviridae (4 genera)
- looks like a crown
1. Infectious bronchitis virus - bronchitis
2. Enteric corona virus (enteritis)
3. SARS virus - severe acute respiratory syndrome
- affects people in Asia
4. SARS virus - Covid19
Steps in viral multiplication
- adsorption
- penetration
- uncoating
- replication/synthesis
- assembly
- release
what happens in adsorption
The virus recognizes the receptor and attaches to the cell receptors.
Rabies attaches to the _______
acetylcholine receptors of the nerve cells
Hepatitis virus attaches to ______
receptors found in hepatocytes (liver cells)
what happens during penetration?
Capsid containing nucleic acids penetrated into cell cytoplasm.
What are the different ways of penetration?
- direct penetration
- endocytosis
ex. rubella. herpesviruses - direct fusion
what method is used to inactivate DNA of a host cell?
methylation; adding methyl groups
what happens in adsorption step for enveloped viruses?
attaches to receptors with its spikes
what happens in adsorption step for naked viruses?
simply attaches because there is only a capsid and there are no spikes
what happens during replication in a DNA virus
It is replicated in the nucleus. The virus uses DNA polymerase of the host cell for its own use.
what happens during replication in a RNA virus
They stay in the cytoplasm and use ribosomes for protein synthesis. The original RNA can be also be used as a template for new RNA.
what happens in assembly?
virus particles are put together starting with the capsid
If the virus is supposed to be enveloped, what does it do to achieve that morphology?
When the virus is released from the cell, it will use the dead cell membrane to produce that extra layer of spikes.
What step describes the virus leaving the cell?
release
what will happen to the host cell when virus is released?
it lyses
If a cell doesn’t break, what will happen?
they will commit apoptosis
what does it mean when a virus is oncogenic?
When a virus enters the cell and triggers genes that produce cancer.
what is a virion?
- young viruses that barely left the host cell
- fully formed virus that is ready to cause infection
how many virions can polio produce in one cell?
100,000 particles
what is a lytic cycle?
A virus enters a cell. Multiplies. Leaves the cell. The cell is lysed.
what is a lysogenic cycle?
Virus enters cell. Refuses to reproduce right away. Integrates into the host’s genome. The virus becomes part of the host.
ex. HIV
ex. retroviridae
HIV lysogenic cycle
HIV inserts itself into the DNA of T4 cells and remains there for years (up to 15 undetected). Out of nowhere, it goes lytic and starts the killing of cells.
why is HIV so deadly?
It attaches to the T4 cells, the cells produce antibodies
what is a bacteriophage?
viruses that attack bacteria
what type of viruses undergo lysogeny?
temperate viruses
what is a prophage?
a bacteriophage that inserts its genome into the DNA of bacteria
what is a provirus?
when the genome of the virus is inserted into the DNA of a eukaryotic cell
what is the relationship between Hepatitis B and delta agent?
In order for the delta agent to become more virulent, Hepatitis B needs to be present. When Hepatitis B is present, the delta agent is able to reproduce, causing Hepatitis D.
what are viroids?
extremely small viruses
what happens in synthetic virology?
Scientists remove DNA from capsid and replace with new DNA.
what are prions?
- infectious particles (defective proteins) that infect other proteins through touch
- not viruses
what diseases are prions responsible for?
lethal brain diseases
ex. Mad cow disease
ex. kuru
how are viruses cultivated?
Commonly in embryonated chicken eggs. Location depends on the virus. They are then harvested to produce vaccines.
how are animals used to cultivate viruses?
Hepatitis C only grows in chimpanzees, so that is the only way they can be studied.
what is meant by in vivo cultivation?
cultivation in a living organism
what is meant by in vitro cultivation?
cultivation in tissues/cells
- more controlled
what is the current technique for viral identification?
Polymerase Chain Reaction (PCR)
how does the PCR identify?
by multiplying pieces of DNA
what is the goal of viruses?
to reproduce
what is the most effective method of controlling viruses?
vaccination
how long does it take the body to produce antibodies against a newly encountered virus?
two weeks
what cream can alleviate symptoms of herpes virus?
acyclovir
