Flashcards in Lecture 9 Deck (79):
acellular particles which are capable of infecting host cells and causing disease, requires a host in which to multiply (obligate intracellular parasites)
-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
viruses can infect animals, plants, fungi, protozoa, and bacteria. most are specific for single host species
To be able to infect a cell the virus must recognize ..
particular features on the host cell surface (HIV and CD4 immune cells)
very small and viewed w/ electron microscope, range from 20-1000 nm in length
Nucleic acids of viruses
may have DNA OR RNA not both, always the same as it is a characteristic
Virus genetic material can be either ..
double or single stranded RNA or DNA
Nucleic acid may be
-linear or circular
-segmented (arranged in many pieces) or single molecule
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
Total amount of nucleic acid in a virus varies from..
a few thousand to 250, 000 base pairs
protein coat surrounding the nucleic acid, provides shape to virus
individual proteins that make up the capsid
The capsomere arrangement is..
characteristic of a particular virus
nucleic acid and the capsid together (minimal required structure for a virus)
not present in all viruses, is a lipid bilayer (membrane) acquired from the host cell
If envelope is present, the envelope is..
the external coating around the nucleocapsid
additional viral proteins that may be inserted into envelope
Viruses are either ..
Morphology of viruses is based on the..
shape of the capsid
3 morphology of a virus
long rods either rigid or flexible
usually icosahedral (20 triangle faces) while other geometric shapes are possible
roughly spherical, dictated by the lipid bilayer
complicated structure, may have additional protein structure attached to capsule
Most common complex virus..
bacteriophages (infect bacteria)
Classification of viruses are based on..
-nucleic acid type
-envelope presence (important)
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
6 multiplication steps of animal viruses
-maturation and assembly
attachement to the host cell, viruses have attachment sites which are potations or glycoproteins within the host membrane that the virus recognizes
entry into host cell
Naked viruses enter the host cell via..
Some enveloped viruses enter the host cell via..
fusion (lipids of the envelope fuse with he host cell plasma)
separation of viral nucleic acid from the capsid
makes used primarily of host metabolic enzymes, viral nucleic acid is replicated
DNA replication occurs in the _______ during biosynthesis
nucleus of host cell
RNA replication occurs in the _____ during biosynthesis
Both DNA and RNA viruses have the..
viral proteins synthesized in the cytoplasm
Maturation and assembly
new virus particles are assembled from nucleic acids and capsomeres. nucleocapsids are formed
naked virus bursts out of the host cell, host cell ruptures and dies. Enveloped virus buds out of the host cell (pushes through membrane)
the envelope forms form the plasma membrane, there is steady release of mature enveloped viruses over time, host cell remains alive long time
The host defences play..
a major role in the outcome of viral infections, protects against an otherwise lethal infection
Most healthy human carry a number of..
-antibodies for viruses
If a virus is transferred from the immune host to another individual it can result in...
Types of infection
-acute infection with late complications
-persistent viral infection
-latent viral infection
-chronic viral infection
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
Lysis of the infected host cells cause..
the release and spread of virus particles
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
Example of acute infection with late complications
measles can go on to cause subacute sclerosing panencephalitis (SSPE) (fatal brain disorder)
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
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
Latent viral infections
acute infection is followed by an symptomatic period, can be reactivated years later, symptoms may be diff when reactivation occurs
virus inserts a cop of its DNA into the host cell chromosome
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
Chronic viral infection
after an acute infection, infectious virus reminds present at all time (may or may not cause noticeable symptoms)
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
Viral DNA can transform normal animal cells into..
malignant cancer cells
genes required to stimulate normal cell growth, animal cells have these
Tumor supressor genes
inhibit cell growth
When mutations occur in these genes it results in..
uncontrolled cell growth which leads to tutor formation and cancer
Cancer mutations can occur as a result of..
mutagens or carcinogens
carry oncogenes, viral DNA is inserted into host cell chromosomes, may have oncogenes present in viral DNA
interfere with cell control mechanisms
Oncogenic viruses cause proto-oncogenes to ..
be over expressed, leading to increase transcription which leads to it becoming a oncogene
Human papilloma virus (HPV)
sexually trasmitted virus which causes genetical warts, cruise is believed to cause almost all cases of cervical cancer
Possible oncogenic viruses
-human papilloma virus
-hepatitis B virus and hepatits C virus
Epstein-Bafrr virus (EBV)
causes infectious mononucleosis, may cause lymphoma (cancer of white blood cells) and some cancers of nose/throat
Hepatitis B virus (HBV) and hepatitis C virus (HPV)
is believed to cause almost all cases of liver cancer
Virus-like infectious particles
single piece of RNA, naked RNA with no protein coat, results in some plant disease (NOT in animals)
infectious protein particles, no genetic material present, linked to several fatal human and animal diseases
Example of a prion causing disease
transmissible spongiform encephalopathy (TSE) where brain functions degenerates as neurons die, form sponge like holes in brain
Most frequently prions are carried in..
sheep infected w/ prions
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
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)
Prion disease is..
always fatal and there is no treatment of cure
(NP) protein normally doesn't cause any harm but no known function
Infected animals have same NP but it is..
in a diff form as a prion protein (PP)