virus-detailed Flashcards
what is a virus?
a virus is a pathogenic particle which acts as parasite and capable of replication only within a host cell
what is a parasite?
organism that lives in or on a host
what does it mean by viruses are obligate intracellular organism?
carry out reproduction by parasitizing host cells
what is a host cell?
a living organism which provides food and shelter for growth of other organisms such as parasites
what is a vector?
living organisms that transmits the infectious agent such as virus from one infected organism to another
describe in detailed the structure of a virus
- contains a nucleic acid core which could either be DNA or RNA
- nucleic acid core contains virion associated polymerase which has a role in genome replicate and transcription
- a protein coat called capsid protects the nucleic acid and together the protein coat and genome make up the nucleocapsid
- the capsid is made up of protein sub unit, known as capsomeres
- a phospholipid layer containing protein spikes for attachment on receptor of host cell
where exactly does the protein spikes of viruses attach to?
1- protein which act as receptor
2- lipids
3- carbohydrate chain found on glycolipid and glycoproteins
what is the typical size of a virus?
20 to 200 nanometer usually
what are the 2 main morphology of viruses and describe?
helical
-the capsomeres spiral up with the genome within the center
icosahedral
- contains 6 faces and protein spikes
what is a virion?
an infectious virus particle which is complete containing capsid, nucleic acid or even a phospholipid layer
what is a viral?
infectious agent which has a high level of redundancy
*2 or more genes perform the same biochemical function
what is a viroid?
an infectious virus particle which is in complete, only containing RNA without a protein coat
what is a proteolytic enzyme?
protease enzyme which break down or build up proteins
describe the general virus replication
1- virus attaches and enters host cell
2- disassembly of the virion occurs, revealing its nucleic acid, protein, etc
3- the viral genome enters the nucleus and gets
a}- replicated
b} Transcripted- DNA to RNA
4-the RNA, is translated outside the nucleus forming the virions proteins
5-the protein and replicated genome gets assembled to form more virions and is released
how does virus replication occur when using RNA
the RNA is injected into host and an enzyme known as reverse transcriptase, converts the RNA to DNA which can then be used normally in the steps of virus replication
what is the problem of RNA viruses such as HIV?
during the reverse transcription of RNA to DNA, the DNA is not checked for any mistakes, leading to mutations and variations between viruses
describe the lytic cycle{ active }
1- the virus binds to receptor of host cell and injects its viral genetic material into it
2-the viral genetic material takes over the host functions and starts transcribing and replicating its own DNA
3-once all the new materials are made, assembly of the new virion is made
4-due to increase in number of new virion, lysis of the cell occurs to release new viruses
what is the problem of cell lysis?
cells cannot survive without its cell membrane
what happens to other viruses inside the host cell when lysis occurs?
* host cell is multicellular
the virus can either use its own genetic material for replication or the new genetic material to infect other cells
describe the lysogenic cycle[ hidden]
1- virus attaches to the host cell and injects its genetic material
2-the genetic material stays hidden within the genetic material of the host cell
3- the host cell multiplies normally, replicating the viral DNA as well
4-a trigger such as lack of food for host cell or a chemical trigger occurs
5- the trigger causes the viral DNA to separate and go into the lytic cycle
in which cycle of replication can the host cell [in this case a microorganism one] be made more or less pathogenic [ cause disease]
in the lysogenic cycle/ hidden
what are the 5 phases and stages of replication and describe them
1- absorption- virus attachment
2- penetration-injection of genetic material
3- eclipse- starting of virus infection
4- doubling- replication of virus
5-virus exit phase-lysis of cell membrane
what are 4 examples of common viruses
1- influenzas A virus 2- poliovirus 3-bacteriophages 4-HIV 5- hepatitis B virus
what is a cytopathic effect
structural change in host cell caused by viral invasion
which virus cause cells to become large granular clumps resembling bunch of grapes?
adenovirus
which virus cause cells to become multi-nucleated?
herpes virus
why do some cells become multinucleated as a cytopathic effect
1- fusion of cells
2- division of the nuclei
viruses which cause these transmission 1- respiratory transmission 2- faecal-oral route 3- blood-borne transmission 4-sexual transmission
1- influenza A virus
2-enterovirus[poliovirus]
3- hepatitis B virus
4- HIV
What is virus tissue tropism?
the ability of a virus to infect specific cell tissue
which cell does HIV infect?
CD4+{ a type of white blood cell}
Which receptor does poliovirus attach to?
CD155
What are 3 the classification of virus according to the host cell and describe them?
1- animal virus: effects humans and animals animal: chicken plague humans; chicken pox, small pox plants: virus that infects silkworm and butterflies 2- bacteriophages infects and dissolve bacteria cells 3- plant virus: infect plants eg; tabaco mosaic virus
what is in vivo disease process?
research or work done within or on a living organism to study the disease process
why are diseases caused by viruses?
1- cell destruction
*following an infection
2-virus-induced changes to gene expression
*inhibits gene expression in host cell
3- immunopathogenic disease
* viruses cause change of immune response
what is gene expression?
process of turning on a gene in a cell to make RNA and proteins
what is immunopathogenic disease?
process of disease development involving an immune response
describe the way vaccines work
1- weakened form of pathogen injected into the body2- activation of the active immune systema}phagocytosis by phagocytesb}lymphocytes make antibodies
: antibodies attach to antigen on pathogens and destroy by alerting phagocytes or enzymic reaction
:lymphocytes remains as memory cell
describe the 2 types of immunity
active immunity
- developed after containing pathogen in the body
eg: vaccination
passive immunity
- provided by antibodies or antitoxins from outside the body
eg: injection of antibodies or breast milk
describe the acute virus infection graph
x-axis: time y-axis: amount of virus
- as the time goes by and the amount of viruses increases, the symptoms increase slowly until an optimum and then decreases
- the ending indicate that either host cell died or infection was resolved by innate immune response
what are 2 features of acute virus infection?
1- localized to specific site of the body
2- development of viraemia with widespread infection of tissue
* viraemia-virus in the bloodstream
describe virus induced tumor
1- virus enters uninfected cell
2- virus nucleic acid combines with cellular genome
3- virus genome takes over the cell
4- uncontrollable cell multiplication causing tumor formation
what are ways for treatment and prevention of virus infection?
1- antivirals targeting
2- vaccination/immunization
what are 4 antivirals target?
1- attachment prevention
2- nucleic acid replication prevention
3-virus protein process prevention
4- virus maturation prevention
what tumors do these viruses cause 1- human T-Cell leukemia virus [HTLV-1] 2- Epstein bar virus 3- human papillomavirus 4-hepatitis C virus
1- leukemia
2- Burkitt's lymphoma
3-a} benign warts
b} cervical carcinoma
4-liver carcinomawhat are polioviruses properties
1- enterovirus
2- has an RNA genome
3- transmitted by fecal-oral route
4- causes poliomyelitis and gastrointestinal problems
describe a poliovirus infection
1- virus enters the body via food and water
2- the virus enters guts
3- virus enters blood[ viraemia]
4- a]virus enters non-neuronal tissue
b] virus enters neuronal tissue
5- if virus enters neuronal tissue, paralysis occurs
why does paralysis happens due to poliovirus entering the neuronal tissue?
never cells gets destroyed so muscles doesn’t receive signal from the CNS[ brain+ spinal cord]
describe the incidence of poliomyelitis
x-axis; year y-axis; number of cases
- the graph starts from the top and decrease,
- the first decrease is by using inactivated vaccine and the greatest decrease is by using live weakened vaccine
define inactivated virus
vaccine made from proteins or other small pieces of a pathogen
what are the properties of Influenza A virus?
1-myxovirus: any group of RNA viruses 2-enveloped virus 3- contains an RNA genome 4- infects animals and humans 5- undergoes antigenic variation 6- causes respiratory illness
define antigenic variation
alteration of the protein or carbohydrate on infectious agents to avoid host immune response
describe influenza A virus infection
1-spreads by respiratory route
2-infects cell in respiratory tract
3- respiratory epithelium gets destroyed
4- secondary bacterial infection
what is secondary bacterial infection?
infection caused by bacteria after the treatment of the first
what occurs in the secondary bacterial infection after influenza A virus infection
altered cytokine expression causing fever
what is a cytokine?
a cell signaling molecule that help cell to cell communication in immune response
what is an example of a cytokine?
1- interlukin-1
2- interferon
what are the 2 types of generation of influenza A virus
1- antigenic shift involved
2-antigenic drift involved
what is an antigenic shift?
mixing of genes from influenza viruses from different species
what is an antigenic drift?
accumulation of minor genetic mutations
describe the generation of influenza A virus involving antigenic shift
Human H2N2 gene and Avian H3N8 gene can go through a antigenic shift to form Human H3N2 gene
describe the generation of influenza A virus involving antigenic drift
human H2N2 gene forms H2N2 gene However the HA and NA gene get mutated
