BSC 438 Virus Lecture

Why is it difficult to get antivirals for viruses?

viruses use materials from your cells to replicate, so if you stop the viruses, you can kill your cells

Can all life forms be infected by viruses?

Yes

What is a virus?

noncellular particle that must infect a host cell, where it reproduces

What does a virus do to a cell’s machinery?

subverts the cell’s machinery and directs it to produce viral particles

What consists a virion?

complete virus particles

contains a nucelocapsid which is composed of nucleic acid (DNA or RNA) contained within a protective protein capsid (in more complex viruses, the protective protein may be called a head coat)

What is a bacteriophage?

virus that infects bacteria

What do bacteriophages form?

plaque of lysed cells on a lawn of bacteria

What is a virologist?

scientists that study viruses

What is virology?

study of viruses

What is thought to have been among the causes for the decline of the Roman Empire?

epidemics caused by measles and smallpox viruses

Lady Wortley Montagu

she would inoculate children with material from smallpox lesions of mild cases (mixed success caused this to become a common practice)

Edward Jenner

published case reports of successful attempts to prevent smallpox by exposure to cowpox

would use criminals and orphans to see if they could prevent smallpox

Can a virion reproduce?

cannot reproduce independent of living cells nor carry out cell division as prokaryotes and eukaryotes do

Enveloped viruses

virions having envelopes

Naked viruses

virions lacking envelopes

Host range

the particular group of host species that each species of virus infects

Acute viruses

rapidly kills their host, acts as predators or parasites to limit host population density

If the population becomes dense enough, the virus is transmitted easily, and an epidemic will occur that lowers the population

Relationship between virus mortality and genetic diversity

it may increase genetic diversity

Virion size range

10-400 nm in diameter, with most viruses being too small to be seen with a light microscope

Role of the capsid in virus structure

packages the viral genome and delivers it into the host cell

Capsids can be symmetrical and asymmetrical

Promoters

protein subunits that serve as a protein coat for the virus that protects viral genetic materal and aids in its transfer between host cells

usually only one or a very few proteins make up a protein coat (very efficient- need very little genetic material)

Icosahedral viruses

in some, the capsid is enclosed in an envelope formed from the cell membrance of the host

Viral Envelopes

contains glycoprotein spikes, which are encoded by the virus

Viral genomes can be…

DNA or RNA

Single or double stranded

linear or circular

What is used as the basis of virus classification?

viral genomes

Tropism

the ability to infect a particular tissue type

receptors determine the viral tropism

ebola has broad tropism while papillomavirus only infects epithelial tissue

DNA Viruses Replication

can utilize the host replication machinery

RNA Viruses Replication

use an RNA-dependent RNA-polymerase to transcribe their mRNA, which is error-prone and leads to mutations

Retrovirus Replication

use a reverse transcriptase to copy their genomic sequence into DNA for insertion in the host chromosome

What do all animal viruses use to make proteins?

host ribosomes

Where does translation occur?

cytoplasm

What is the assembly of new virions?

form capsid and the genome

may occur in the cytoplasm or nucleus

th envelope proteins are inserted into a membrane (cell membrane or organelle membrane)

What are the two mechanisms to release progeny viruses from the host cell?

lysis of cell or budding

Budding

virus passes through the membrane and the membrane lipids surround the capsid to form an envelope

all enveloped viruses bud from a membrane (plasma membrane or organelle membrane)

How are bacteriophages cultured?

in batch culture (liquid) or as isolated plaques on a bacterial lawn (on a plate)

Step Curve

generated by batch culture of viruses