Virology exam 1 review

Variolation (inoculation)

the method first used to immunize an individual against smallpox with material taken from a patient in the hope that a mild, but protective infection would result

what was variolation later improved to and by whom?

vaccination by Dr. Edward Jenner

The filtering device shown in the ppt had porcelin pores too small for bacteria to pass through, but ..........

something smaller than bacteria was able to pass through (aka viruses)

what type of microscope is needed to see viruses?

electron microscope

CPE (cytopathic effect)

a visible effect on a host cell, caused by a virus, that may result in host cell damage or death
ex. changes in cell morphology

CPE: Syncytium formation

adjacent cells merge into a continuous mass
(glob)

CPE: inclusion bodies

compacted masses of viruses or damaged cell organelles in the nucleus and cytoplasm

CPE: loss of contact inhibition

-Cells will now pile up on each other
-Normal cells stop dividing when in contact with other cells

who created the rabies vaccine?

Louis Pasteur

types of vaccines

1. prophylaxis (pre exposure)
2. post-exposure

How do attenuated vaccines work?

create a weaker infection that trigger immune response and memory without the full blown disease

Baltimore Classification Scheme

based on relationship of viral genome to its mRNA

Baltimore Classification Scheme Class I

dsDNA
ex. herpes

Baltimore Classification Scheme Class II

ssDNA that requires an intermediate
ex. Parovirus

Baltimore Classification Scheme Class III

dsRNA
ex. Rotovirus

Baltimore Classification Scheme Class IV

ssRNA that requires an intermediate
ex. Coronavirus

Baltimore Classification Scheme Class V

ssRNA that does not require an intermediate
ex. Radbdovirus

Baltimore Classification Scheme Class VI

ssRNA that uses reverse transcriptase to be dsDNA
ex. retrovirus

Baltimore Classification Scheme Class VII

dsDNA that is too short and uses a ssRNA intermediate
ex. hepadenovirus

one step growth curve

demonstrates the multiplication of viruses

Viral replication Cycle

1. attachment
2. entry
3. uncoating
4. genome replication
5. gene expression
6. assembly
7. release

IRES

internal ribosome entry site

acute infection

comes on rapidly, with severe but short-lived effects

chronic infection

progress and persist over a long period of time
slow replication
ex. HPV

latent infection

Persistent infection with recurrent symptoms that "come and go"
ex. chickenpox

prophage

the viral DNA that is embedded in the host cell's DNA

host range

The limited range of host cells that each type of virus can infect and parasitize.

how does a virus enter the body?

1. respiratory tract
2. GI tract
3. bloodstream
4. GU tract
5. eyes
6. skin

how of the host range is determined by

viral attachment

host receptors also determine

tissue tropism ( what can be infected)

attachement is dependent on

capsid proteins
NOT genomic payload

what is an example of a virus that is acute latent?

varicella-zoster (chickenpox will later cause shingles as some of it stays hidden)

viruses typically bind when the

spike proteins binds to receptor

what will a virus do if it cannot immediately find a receptor?

weakly attach and tumble down till it can find a receptor

HMO

-human milk oligosaccharides
-80% chance that child won't get HIV from breast milk if it is HIV - at birth

what part of the HIV envelope iniates attachement?

SU (gp120)

CD4

primary host receptor

how do we find host receptors for viruses?

1. molecular cloning
2. affinity binding
3. immunological approach

affinity binding

isolate cell surface proteins -> immbolize proteins in chromotography column -> test for virus binding

immunological approach

mix virus w/ cell protein extract -> chemically induce crosslinking -> look to see what has bound to virus

molecular cloning

mRNA from permissive cell is obtained and converted into cDNA library -> inserted into nonpermissive cells (one of which will now contain the receptor protein ) -> a previosly non permissive will become permissive -> recover and sequence

what is critical in transitioning from attachement to uncoating

fusion protein

fusion can take place

-plasma membrane
-internally (more common): endosome or lyzosome

typicall when something comes from the exterior of the cell to the interior, it becomes more

acidic, but some viruses take advantage of that

how are the more important receptors determined

inducing certain mutations

influenza spike proteins

1. Hemagglutinin (HA)
2. Neuraminidase (NA)

what type of virus does not require a fusion protein

naked virus
ex. polio

fusion of enveloped virus

virus just fuses in

endocytosis of an enveloped virus

engulfed
vesicle forms around viral envelope
most animal virues

gp41

fusion protein

gp120

primary binding protein

what dictates where most of the replication will take place

genome

viruses will utilize what to carry the virus to the nucleus?

cytoskeleton

what is an example of a virus that has replicates unusually?

Reovirus

how do plant viruses infect?

through broken/damaged parts (mechanical destruction from insects chewing)
reproductive structures are also susceptible

what structure in plants allow the spreading of a virus once its in?

plasmodesmata

plant immune defense

chemicals that kill the tissues before further spreading

sigma factor

helps direct RNA polymerase where to start

T7 DNA replication proteins

1. gp 2.5 (viral) : ss binding protein
2. gp 4 (viral): helicase and primase
3. gp 5 (viral): polymerase
4. Trx (host): aid processivity

MS2 genes (4)

1. coat
2. RdRp gene
3. A protein
4. lysis protein

what is RdRp

RNA dependent RNA polymerase

which MS2 gene is in high abundance?

coat

which MS2 gene is in low abundance?

lysis

the phi chi 174/phi x 174 has a ___________ genome

circular

bacteriophage lambda

-dsDNA

how are the genes in bacteriophage lambda expressed? (3)

1. immediate early
2. delayed
3 late

if the virus has a complicated structure, you can assume that there are lots of

enzymes
structural proteins
genome

under good growth conditions, bacteriophage lambda favors

lysogeny

under poor growth conditions, bacteriophage lambda favors

lytic

lambda gene expression

1. immediate early
2. expression of N gene (transcriptional antiterminator) and protein (Pl promoter)
3. Cro gene and protein (Pr promoter)

what does the transcribing in bacteriophage lambda?

RNAP

what does the N protein do?

binds to the terminator stem loop and recruits host protein

what does Q protein do?

causes more antitermination which late gene expression

rolling circle replication makes long

concatemers of DNA