Not finished practical virology wk2 one step growth curve practical assessment

infectious diseases

Titre

Concentration of viruses in a sample.

Plaque Assay

Method to quantify virus by counting plaques.

how do you find LD50

complete a quantal assay study in animals. use the Dose causing 50% mortality in organisms. (not working this out in the exam)

Density Gradient Centrifugation

Separation technique based on particle density.

Multiplicity of Infection (MOI)

Ratio of infecting viruses to target cells.

One Step Growth Curve

Experiment showing stages of virus replication.

Eclipse Period

Time with no detectable infectious particles.

Rise Period

Time when mature virions are released.

Burst Size

Number of phages produced per infected bacterium.

Progeny Viruses

Viruses produced from an infected cell.

Fluctuation Test

Experiment demonstrating spontaneous mutations in bacteria.

Bacteriophages

Viruses that infect and replicate within bacteria.

Artificial Lysis

Inducing cell death to study virus yield.

what methods can be used for determining virus titre

plaque assays

quantal dose response (LD50)

hemagluttination

how can we find the structure of a virus

electron microscopy and x- ray crystallography

how can we detect the presence and function of a virus

detection=

• serological methods ( using proteins and antibodies)

• viral nucleic acid, sequencing

function=

using tissue culture in animals

how do you perform a plaque assay

create a serial dilution of a virus plate this onto susceptible cells (bacteria) semi solid media will either be mixed before or added now to restrict diffusion of virus particles - to only infect neighbouring plaques and so they can be seen) restricted cell to cell soread of virus results in localised destruction of cell monolayers which show as plaques- little dots- of killed bacteria/cells

how do you calculate the amount of virus from the plaque assay (PFU/ml)

plaque no/ volume of sample plated (ML) x dilution

How did Hershey and Chase show that DNA is passed to new phages in phage reproduction? 1952

used 2 samples of phage T2.one sample was labelled with radioactive phosphourus and infected e.coli, homogenised and then centrifuged to separate the bacterial cells and phage coats. results were analysed and supernatant contains 25% radioactivity whilst the pellet (phage coats) had 75%- meaning phage are using the DNA and its not remaining on the bacteria insteadwhen repeated with labelled sulphur, the supernatant had 85% radioactivity showing the phage inserted DNA into the bacteria

how did luria and delbruk find out about mutations

observed resistant bacteria in two phage experiments. when mutations were induced, there would be limited variability in the simple. with spontaneuos mutation they were highly variable

what does one step growth curve show

ellis and dubruck 1939,

showing that viral re1.plication is in stages.

1. initiation of infection

2. replication and expression of virus genome

3. assembly and release of mature virions from infected cells

   key is to synchronise culture so all cells are infected at t=0

what happens in latent period

eclipse period- no infectious particles. none are released as viral dna is inserted into bacteria. intracellular accumulatio, the viruses are assesmbled but not released

artificial lysis of cells can show eclipse and intracellular accumulatio period