viruses Flashcards
what are viruses
They are simple, acellular entities of one or more molecules of DNA or RNA not both and are enclosed in a coat of protein, lipids or carbohyratesand can only reproduce in living cells- obligate intracellular parasites
examples of airborne disease
chickenpox, shingles, germen measles (rubella) and influenze
examples of arthropod borne disease
yellow fever arbovirus
examples of direct contact diseases
AIDS, cold sires, common cold, genital herpes, rabies and hepatitis
examples of food-borne diseases
polio and infectious hepatitis
examples of other virueses
warts, verucas, HPV
what is the geonme of a viruse
RNA or DNA, double or single stranded, segmeted or non-segmented
what is the compoisition of the envelope
lipids from host cell membrane, proteins and glycoproteins
what is the function of the enevlope
camoflage and recognition and attachment to host cell
what are capsids
the proteins forming the virus shell. they are rings
what is verial shape
helical or isometric (cubic). the number of protein molecules in the virus are large but rarely more than one
what are icosahedral capsids
form ring shape units called capsomeres- 5 or 6 protomers
explain the classification of viruses
host range= very specific, but can jump between species through mutations
envoloped or non
type of nucleic acid= single or double
shape= different shapes
what is the size of viral shape
10-500nm and 1000 microletersin a naometre
what is icosahedral
polyhedron with 20 triangular faces
what is helical
hollow rigid or flexible cylinders
what is envoloped
outer membranous layer surrounding either of the 2 above shapes
what is complex
they have a head (icosahedral) and a tail (helical) and other parts
what happens to viruses if they are left for long periods
they crystalise
explain intracellular and extracellular
extracellular- outside of cell- they dont breath or have any activity
intra- inside the cell
attaches to chromosome and then becomes alive
how did viruses used to be cultivated
old way was using fertilised chicken eggs 6-8 days after fertilisation . Different viruses like different parts of the embryo and when it grows it forms pocks
what are used more now
use animal and plant tissue cultures- monolayer of cells or protoplasts,causing plques or necrotic lesions or abnormalaties called cytopathic effects
why are bacterial and fungal antibiotics needed on cultures
the media we use for tissue cuultures are rich and stop growth and allow viruses to grow we need bacterial and fungal antibiotics
what are bacteriophagus cultivated in
broth or agar cultures - results in clearing of broth or plaques on agar plates
what are the signs of viral propagation
death of an embryo
plocks on membranes
plaque- disease that affects humans and other mammels
necrotic lesions that lead to discolouration of skin
what are the techniques for isolating viruses
centrifugation, precipitation, denaturation and enzymatic denaturation
types of centrifugation
differential or gradient
what is precipitation
using ammonium sulphate followed by centrifugation
what is denaturation
using heat, pH changes or solvants and may inactivate the viruses
what is enzymatic denaturation
looks into cell components leaving viruses unharmed
what is LD50
lethal dose- amount of ingested substance that kills 50% of a test sample
what is ID50
Infected dose- inoculum required to infect 50% of a population
tools used to study viral replication and mechanisms can be carried through…
enumerationand measuring infectious units
what are PFUs
plaque/ pock forming units
