Lecture 4-1: Viruses

virus

submicroscopic particles whose genomes are of nucleic acid that replicate inside cells using the cellular synthetic machinery for production of progeny virions

Genetic material will EITHER be

RNA or DNA

Capsomere

morphological subunit from which virus capsid is built (legos)

capsid

protein shell or coat that encloses nucleic acid genome, built by capsomeres

envelope

lipid containing membrane that surrounds some viruses, surrounds capsid

nucleocapsid

capsid together with enclosed nucleic acid

virion

complete infective virus particle

incomplete virion

virion without nucleic acid “empty capsid”, mistake during replication

pseudovirion

capsid encloses host nucleic acid instead of viral nucleic acid, wrong genetic material, won’t replicate

provirus

viral DNA has integrated into host cell chromosome in latent stage and must be activated before transcribed, produces virus particles, transmitted from parent to daughter cell (virus is hitch-hiking on host cell DNA)

characteristics of a virion

consist of nucleic acid surrounded by protective protein capsid, 20nm-300nm in size [very small], few genes [4-200]

RNA or DNA can be 

single or double stranded

Most DNA contain all their genetic information in a _____ linear molecule.

single

RNA viruses can be _____ or contain ________.

linear; segmented genomes, which have several different RNA molecules in their capsid (each one carrying the same or different genetic information)

Viruses lack cellular components

necessary to generate energy and synthesize proteins (they have to hijack cells)

Viruses have very few ____, which are involved with getting into the cell and then replication of nucleic acid once they do get in the cell.

enzymes

Viruses have a limited amount of genetic information which includes

info to make protein coat, info to replicate its own chromosome, and info to move the virions in and out of the host cell

Shape is determined by ____, which can be ____ or _____.

capsid, helical/isometric or spherical

Spherical will look rounder if it has an

envelope

Isometric/spherical is shaped as

little triangles coming together

Helical is shaped like a

cylinder

Naked virus

just has protein coat and genetic material

Enveloped virus

nucleocapsid is contained within envelope with ‘spikes’ on it, the envelope is mainly coming from host cell and adds protection

Some viruses can have an additional _____ that comes from the cytoplasmic membrane of an infected cell

envelope with a double layer of lipids

An invelope can

protect a virus and possible help it invade parts of the immune system

The ______ is inside the lipid envelope.

protien matirx

What do envelope spikes do?

attach virion to host cell

Zika virus

RNA, headaches, strong link between maternal virus to microcephaly (small baby head)

First step in viral replication

phages attach to host receptors (bacterium)

Second step in viral replication

Penetration in viral replication, viral nucleic acid enters the host cell

Penetration: Lysozyme (at tip of tail) lyses the ______ and allow genetic material to enter.

cell wall of host

During penetration, the tip of the tail opens and _____ DNA in the head passes through the channel and is injected through the cell __ into the cell

linear, wall

Only ____ enters cell during DNA viral replication.

nucleic acid

Third step in DNA replication is

transcription/translation

During transcription

phage DNA transcribed leading to the production of specific proteins

Part of the DNA is transcribed into 

mRNA mRNA is translated into the proteins that are specific for infecting the cell [ex:nuclease= degrades host cell]

____ DNA is not transcribed, only ____ DNA.

host, phage

The fourth step in DNA replication is

replication where phage DNA copies itself and structural proteins are synthesized, host cell genetic material is gone

The fifth step in DNA replication is

assembly of phage DNA and protein to form mature virions

The last (sixth) step in DNA replication is

release of virions from the host cell

Lysozyme is coded by

phage DNA

Lysozymes digest _______, then you see cell lysis and release of viral particles.

host cell wall from within

Genetic alteration of a host cell includes

latent state, nucleic acid of virus becomes part of a host cell DNA, host cell keeps living and dividing with viral material

Disease of a host cell includes

productive infection, goes through replication process

In productive infection with non-lysis of cells

host cell multiplies and there is continuous leakage of virions

In productive infection with lysis of cells

release virions and host cell will die

Diagnosing Viral Infection: cell culture

living cells (chick embryo )

Diagnosing Viral Infection: Serological techniques

detecting antigen and antibodies

Diagnosing Viral Infection: Direct detection of antigen from specimen

Polymerase chain reaction

Diagnosing Viral Infection: Molecular methods

live or dead rapid tests

Virus isolation must be collected within ______ of onset of the illness.

the first few days

Specimens should be stored at ___^oC for no more than ___ days.

4-8, 1-3

You can freeze virus at

-70c

______ will cause loss of infectivity.

temperature recycling