N251 exam 4: lecture 1

virus

Genetic material + protein coat

Either DNA or RNA, never BOTH

They can be in Plants, animals and bacteria

host range

range of animal spp and tissue cells that virus can infect (can be broad or limited). Plant, animal or Bacteria

capsomeres

morphological subunits from which the virus capsid is built
-building blocks of capsid

legos of virus

capsid

protein coat surrounding a virus
-protects genetic material

envelope

lipid-containing membrane that surrounds some viruses

-picked up form host cell when they are Leaving

Nucelocapsid

capsid + nucleic acid

virus

RNA or DNA + Protein

tail

helps get a virus into a cell

virion

Virus that has infected a cell and is ready to go infect other cells

incomplete virion

virion without nucleic acid (empty capsid)

car going through assembly line and forgetting to put engine in

Pseudovirions

When the virus engulfs the host’s nucleic acid, rather than the viral DNA.

It does not replicate

provirus

Viral DNA that inserts into a host genome.

-wont form virus but keep getting replicated with the host dna because it is a part of th chromosome.

General Characteristics

Virions are very small (200-300) compared to E.coli with 1000nm.

They contain very few genes 4-200 vs 3000 for Ecoli genes.

either DNA or RNA

DNA or RNA is either single or double stranded, but most DNA have theur genetic material is a single linear molecule; however, the RNA could have either linear or segmented genomes with different RNA in their capsid.

They have no cellular component, so they have to hijack other cells for energy.

The only enzymes they have will help them to replicate and enter other cells.

genectic informaion is used for

Info to move in and out of the cell

Replicate

Make their capsid

Why is segmented RNA a problem

It is harder to create vaccines for them

a lot of research is with

bacteriophage
-easy to study

Viral Architecture

shape of virus is determined by shape of capsid (Helical or spherical)
-each capsid is composed of many identical units (capsomeres)

Some viruses have an additional lipid membrane (envelope)
-usually acquired from cytoplasmic membrane of infected cell- structure is similar, double layer of lipids
-just inside the lipid envelope is protein matrix(capsid)
-spikes project from the envelope and attach the virion to host cell- protein, glycoprotein

poxiviridae

Large, enveloped, DNA, small pox

Parvoviridae

Naked, DNA, gastroenteritis outbreak after eating shellfish

Papovaviridae

Naked, circular DNA, Human Papillomavirus.

helical

cigar shaped
-more column like

spherical/isometric

Triangle shaped

tobacco moasic virus

-very dangerous virus to tomato plants especially peppers
-in all tobacco
-tobacco plant is like mild common cold
-but its relatives like tomatoes and peppers do not have resistance will weaken tomato plants and kill pepper plants
very large virus and very frequently studied

viruses can be

naked:
-nucleocapsid

enveloped:
-capsid
-enclosed in envelop containing lipids and spikes to protect virus
-PICKED UP FROM HOST AS VIRUS EXITS HOST CELL AFTER REPLICATION

hantavirus

associated with rodents
-left behind in urine and feces
-can lay for a while and be dangerous to humans

zika virus

single stranded RNA virus
-single stranded
-transmitted by mosquitos
-shown link to producing microcephaly in babies: if mother is bitten while pregnant and infected

if bitten and infected at an earlier age, immune system will be able to fight infection
-see increases when zika moves into a new area, people do not have immunity against= hypothesis by professor

rna virus

-rna inside
-capsid surrounding it
-membraneous envelope
-glycoproteins on the envelop

Viral Replication: DNA

1. Attachment: phages attach to host cell receptors
2. Penetration:
-viral nucleic acid enters the host cell
-lysozyme located on tip of the tail, lyses the cell wall
-tip of tail opens and linear DNA in the head passes through the channel and is injected through the cell wall into the interior of the cell
-only the nucleic acid not the entire viron enters
3. Transcription/Translation:
-phage DNA is transcribed leading to production of specific proteins
-part of DNA is transcribed into mRNA
-mRNA is translated into proteins that are specific for infecting cell (phage induced proteins)

-one such protein is a nuclease that degrades DNA of host cell
-host DNA is not transcribed, only phage DNA
4. Replication
-phage DNA copies itself and structural proteins are synthesized
5. Assembly
-phage DNA and protein assemble to form mature virions
-some steps involve a self assembly process
6. Release
-virions are released from the host cell
-lysozyme is coded by phage DNA: lysozyme is digest host cell wall from within, cell lysis and release of phage virions (up to 200)

what can happen when a virus infects a host cell

three options

1. Genetic alteration of host cell and LATENT state of virus
-provirus
-nucleic acid become part of the host cell
-will get replicated, cell itself is not destroyed
-has viral DNA and own DNA
-every-time it divides will produce more copies
-may become active at some point or could stay latent for a while

2. productive infection: more viral particles are produced
-sometimes dont kill: make small hole, viral particles will leak out
3. -can kill host and do true lysis of host cell

laboratory diagnosis

-cell culture: living cells (chick embryos)
-serological techniques: detecting antigen and antibodies
-direct detection of antigen from specimen: polymerase chain reaction (PCR)
-molecular methods: live or dead viruses

viral specimens

-upper respitaroy: n/p swabs, nasal, throat

-lower respiratory: endo trach asp, bronch was, bronchial biopsies

-eye swabs

-stools/rectal swabs

-body fluids: csf, bone marrow, serum, blood, saliva

Specimens: collection and storage
-try and collect between first few days of illness
-want a lot of viral particles
-specimens should not be held at ambient temp: deliver to lab on ice
-do not store for more than 1-3 days
-test rapidly
-freezing at -70c or below will preserve indefintely

temperature recyclying

loss of infectivity from refrig-freezer back and forth