Lecture 9 Flashcards Preview

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Flashcards in Lecture 9 Deck (79):
1

Virus

acellular particles which are capable of infecting host cells and causing disease, requires a host in which to multiply (obligate intracellular parasites)

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Virus features

-filterable disease causing agents
-acellular (no plasma membrane)
-contain a single type of nucleic acid (DNA or RNA)
-surrounded by capsid
-very few own enzymes

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Host range

viruses can infect animals, plants, fungi, protozoa, and bacteria. most are specific for single host species

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To be able to infect a cell the virus must recognize ..

particular features on the host cell surface (HIV and CD4 immune cells)

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Viral size

very small and viewed w/ electron microscope, range from 20-1000 nm in length

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Nucleic acids of viruses

may have DNA OR RNA not both, always the same as it is a characteristic

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Virus genetic material can be either ..

double or single stranded RNA or DNA

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Nucleic acid may be

-linear or circular
-segmented (arranged in many pieces) or single molecule

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Pro and con to virus DNA being segmented

pro; useful to make more amounts of certain genes w/o having to make 1000 unnecessary genes
con; you can forget certain genes behind

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Total amount of nucleic acid in a virus varies from..

a few thousand to 250, 000 base pairs

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Capsid

protein coat surrounding the nucleic acid, provides shape to virus

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Capsomeres

individual proteins that make up the capsid

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The capsomere arrangement is..

characteristic of a particular virus

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Nucleocapsid

nucleic acid and the capsid together (minimal required structure for a virus)

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Envelope

not present in all viruses, is a lipid bilayer (membrane) acquired from the host cell

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If envelope is present, the envelope is..

the external coating around the nucleocapsid

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Spikes

additional viral proteins that may be inserted into envelope

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Viruses are either ..

-enveloped
-non-enveloped (naked)

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Morphology of viruses is based on the..

shape of the capsid

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3 morphology of a virus

-helical viruses
-polyhedral viruses
-enveloped viruses

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Helical viruses

long rods either rigid or flexible

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Polyhedral viruses

usually icosahedral (20 triangle faces) while other geometric shapes are possible

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Enveloped viruses

roughly spherical, dictated by the lipid bilayer

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Complex viruses

complicated structure, may have additional protein structure attached to capsule

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Most common complex virus..

bacteriophages (infect bacteria)

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Classification of viruses are based on..

-nucleic acid type
-capsid structure
-envelope presence (important)

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Naming of viruses: family ends with...
genus ends with..
species ends with..

-the suffix viridae
-the suffix virus
-no specific ending, instead viral species are given descriptive name

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6 multiplication steps of animal viruses

-adsorption
-penetration
-uncoating
-biosynthesis
-maturation and assembly
-release

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Adsorption

attachement to the host cell, viruses have attachment sites which are potations or glycoproteins within the host membrane that the virus recognizes

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Penetration

entry into host cell

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Naked viruses enter the host cell via..

endocytosis

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Some enveloped viruses enter the host cell via..

fusion (lipids of the envelope fuse with he host cell plasma)

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Uncoating

separation of viral nucleic acid from the capsid

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Biosynthesis

makes used primarily of host metabolic enzymes, viral nucleic acid is replicated

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DNA replication occurs in the _______ during biosynthesis

nucleus of host cell

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RNA replication occurs in the _____ during biosynthesis

host cytoplasm

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Both DNA and RNA viruses have the..

viral proteins synthesized in the cytoplasm

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Maturation and assembly

new virus particles are assembled from nucleic acids and capsomeres. nucleocapsids are formed

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Release

naked virus bursts out of the host cell, host cell ruptures and dies. Enveloped virus buds out of the host cell (pushes through membrane)

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During release

the envelope forms form the plasma membrane, there is steady release of mature enveloped viruses over time, host cell remains alive long time

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The host defences play..

a major role in the outcome of viral infections, protects against an otherwise lethal infection

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Most healthy human carry a number of..

-viruses
-antibodies for viruses

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If a virus is transferred from the immune host to another individual it can result in...

infection

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Types of infection

-acute infections
-acute infection with late complications
-persistent viral infection
-latent viral infection
-chronic viral infection

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Acute infections

usually very short in duration, disease symptoms result from tissue damage, host defence system gradually eliminates the virus which can take months/days. host may or may not develop long lasting immunity

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Lysis of the infected host cells cause..

the release and spread of virus particles

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Acute infection with late complications

following the period of acute infection some virus particles still remain, number of virus particles present gradually increase over period of yrs. and cause serious disease yrs later

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Example of acute infection with late complications

measles can go on to cause subacute sclerosing panencephalitis (SSPE) (fatal brain disorder)

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Persistent viral infections

infectious virus is present at all times, disease may or may not be present. infected host is able to serve as a reservoir

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Example of persistent viral infections

hepatitis B, transmitted either sexual or via blood, can have acute period or can cause cirrhosis or cancer of liver

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Latent viral infections

acute infection is followed by an symptomatic period, can be reactivated years later, symptoms may be diff when reactivation occurs

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Provirus

virus inserts a cop of its DNA into the host cell chromosome

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Example of latent viral infections

Varivella zoster virus, belongs to herpes can cause chicken pox, remains latent for years and can come back as shingles

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Chronic viral infection

after an acute infection, infectious virus reminds present at all time (may or may not cause noticeable symptoms)

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Example of chronic viral infection

hepatitis B, transmitted by blood/sex. may have acute period, after that viral number stay high for rest of patients life

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Viral DNA can transform normal animal cells into..

malignant cancer cells

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Proto-oncogenes

genes required to stimulate normal cell growth, animal cells have these

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Tumor supressor genes

inhibit cell growth

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When mutations occur in these genes it results in..

uncontrolled cell growth which leads to tutor formation and cancer

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Cancer mutations can occur as a result of..

mutagens or carcinogens

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Oncogenic viruses

carry oncogenes, viral DNA is inserted into host cell chromosomes, may have oncogenes present in viral DNA

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Oncogenes

interfere with cell control mechanisms

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Oncogenic viruses cause proto-oncogenes to ..

be over expressed, leading to increase transcription which leads to it becoming a oncogene

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Human papilloma virus (HPV)

sexually trasmitted virus which causes genetical warts, cruise is believed to cause almost all cases of cervical cancer

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Possible oncogenic viruses

-human papilloma virus
-epstein-barr virus
-hepatitis B virus and hepatits C virus

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Epstein-Bafrr virus (EBV)

causes infectious mononucleosis, may cause lymphoma (cancer of white blood cells) and some cancers of nose/throat

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Hepatitis B virus (HBV) and hepatitis C virus (HPV)

is believed to cause almost all cases of liver cancer

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Virus-like infectious particles

-viroids
-prions

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Viroids

single piece of RNA, naked RNA with no protein coat, results in some plant disease (NOT in animals)

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Prions

infectious protein particles, no genetic material present, linked to several fatal human and animal diseases

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Example of a prion causing disease

transmissible spongiform encephalopathy (TSE) where brain functions degenerates as neurons die, form sponge like holes in brain

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Most frequently prions are carried in..

food

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Scrapie

sheep infected w/ prions

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Variant Creutzfeld-Jakob Disease

scrapie is eaten by cows and they develop mad cow disease, and the cow is eaten by human and develops this disease. occurs several years after infection

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Prions are very resistant and they are ..

not usually destroyed by high temp, can be destroyed by autoclaving in sodium hydroxide (beef is inedible now)

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Prion disease is..

always fatal and there is no treatment of cure

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Normal protein

(NP) protein normally doesn't cause any harm but no known function

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Infected animals have same NP but it is..

in a diff form as a prion protein (PP)

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Prion protein

can convert a NP into PP shape, eventually all NP are converted into PP shape resulting in disease