viruses

Virus

-A tiny, nonliving particle that invades and then reproduces inside a living cell. --contain DNA or RNA

Specific viruses are known to cause ~15% of human cancers

-Burkitt's lymphoma -Hodgkin's disease -Kaposi's sarcoma -Cervical cancer

cancers viruses cause

-Burkitt's lymphoma -Hodgkin's disease -Kaposi's sarcoma -Cervical cancer

Extracellular state

-Called virion -Protein coat (capsid) surrounding nucleic acid -Nucleic acid and capsid also called nucleocapsid -Some have phospholipid envelope -Outermost layer provides protection and recognition sites for host cells

intracellular state

-Capsid removed -Virus exists as nucleic acid; the virus is inside the host.

Capsid Morphology

-Capsids: protein coats -Protection for viral nucleic acid -Attach to host's cells -Composed of subunits called capsomeres -Capsomere: single or multiple types of proteins

ssDNA viruses

-Cells do not use ssDNA -Parvoviruses have ssDNA genomes -Host enzymes produce DNA strand complementary to viral genome to form dsDNA molecule -dsDNA used for viral replication and transcription

Culturing Viruses in Cell (Tissue) Culture

-Cells isolated from an organism and grown on a medium or in a broth -Cell cultures sometimes inaccurately called tissue cultures

Attachment of animal viruses

-Chemical attraction -Animal viruses do not have tails or tail fibers -Have glycoprotein spikes or other attachment molecules that mediate attachment

Retroviruses

-Do not use their genomes as mRNA -Use DNA intermediary transcribed by viral reverse transcriptase as template to produce viral genomes

Synthesis of DNA viruses of animals

-Each type of animal virus requires different strategy, depending on its nucleic acid -DNA viruses often enter the nucleus -RNA viruses often replicate in the cytoplasm -Must consider: how mRNA is synthesized, what serves as template for nucleic acid replication

Cell division is under strict genetic control

-Genes dictate that some cells can no longer divide at all -Cells that can divide are prevented from unlimited division -Genes for cell division "turned off" or genes inhibiting division "turned on"

Culturing Viruses in Embryonated Chicken Eggs

-Inexpensive, among the largest of cells, free of contaminating microbes, and contain a nourishing yolk.

lysogeny

-Modified replication cycle -Infected host cells grow and reproduce normally for generations before they lyse

Assembly and release of animal viruses

-Most DNA viruses assemble in nucleus -Most RNA viruses develop solely in cytoplasm -Number of viruses produced depends on type of virus and size and initial health of host cell -Enveloped viruses cause persistent infections -Naked viruses are released by exocytosis or lysis

Culturing viruses in plants and animals

-Numerous plants and animals have been used to culture viruses -Laboratory animals can be difficult and expensive to maintain

Culturing viruses in bacteria

-Phages grown in bacteria in liquid cultures or on agar plates -Lysis of bacteria produces plaques -Allows estimation of phage numbers by plaque assay

Characteristics of Prions

-Prion diseases -Spongiform encephalopathies: large vacuoles form in brain -Characteristic spongy appearance -BSE, vCJD, kuru -Transmitted by ingestion, transplantation, or contact of mucous membranes with infected tissues -Prions destroyed by incineration or autoclaving in concentrated sodium hydroxide

The viral envelope

-Protect the virus from being seen by host. Acquired from host cell during viral replication or release; envelope is portion of membrane system of host -Composed of phospholipid bilayer and proteins; some proteins are virally-coded glycoproteins (spikes) -Envelope's proteins and glycoproteins often play role in host recognition

Characteristics of Prions

-Proteinaceous infectious agents Cellular PrP: made by all mammals. normal, functional structure has α-helices Prion PrP: disease-causing form. Has β-sheets Prion PrP: causes cellular PrP to refold into prion PrP

Replication of Animal Viruses

-Same basic replication pathway as bacteriophages -Differences result from presence of envelope around some viruses -Eukaryotic nature of animal cells -Lack of cell wall in animal cells

dsDNA viruses

-Similar to replication of cellular DNA -Viral genome replicated in the nucleus -Viral proteins are made in the cytoplasm Some exceptions: -Poxvirus replication occurs in the cytoplasm -Hepatitis B viruses replicate DNA from an RNA intermediary

Environmental factors that contribute to the activation of oncogenes

-Ultraviolet light -Radiation -Carcinogens -Viruses

Neoplasia

-Uncontrolled cell division in multicellular animal -Mass of neoplastic cells is tumor

lytic replication

-Viral replication usually results in death and lysis of host cell -Five stages of lytic replication cycle -Attachment -Entry -Synthesis -Assembly -Release

Latency of animal viruses

-When animal viruses remain dormant in host cells -Viruses are called latent viruses or proviruses -May be prolonged for years with no viral activity -Some latent viruses do not become incorporated into host chromosome -Incorporation of provirus into host DNA is permanent

fomites

-any nonliving substance or object that transmits infectious material

Hosts of viruses

-most viruses infect only particular host's cells (due to affinity of viral surface proteins for complementary proteins on host cell surface); may be so specific they infect only a particular kind of cell in a particular host.

Bacterial phages

Bacterial virus

Benign vs. malignant tumors

Benign: does not spread Malignant: does spread (cancer)

Viruses kick out

DNA from host membrane and replace it with their DNA.

genetic material of viruses

DNA or RNA

True or false: viruses are cells

FALSE, not a cell, needs a host to replicate.

True or false: a virus can replicate independently

False, need a host to reproduce

Are viruses alive?

No. Some consider them complex pathogenic chemicals. Others consider them the least complex living entities (Use sophisticated methods to invade cells. Have the ability to take control of their host cell. Are able to replicate themselves).

temperate phages

Prophages - inactive phages

True or false: a virus cannot carry out any metabolic pathway

TRUE (no ribosomes)

metastasis

The spread of cancer cells.

TF: Some vaccines prepared in chicken cultures

True

TF: viruses cannot grow in media

True- need a host

TF: Fertilized chicken eggs are often used

True. Embryonic tissues provide ideal site for growing viruses.

Viruses do not have....

a cytoplasmic membrane, cytosol, or organelles.

Attachment

an adsorption process. attachment and penetration.

viruses can infect...

bacteria, algae, fungi, protozoa, plants, animals

Viruses have......

extracellular and intracellular states

generalists

infect many kinds of cells in many different hosts

opportunist infection

infection that develops in a person with a weak immune system

Viruses cause....

infections of humans, animals, plants, and bacteria.

lysogenic conversion

results when phages carry genes that alter phenotype of a bacterium.

glycoproteins

spikes.

phage receptors

surface markers that allow tales to bind.

TF: Viruses cause 20-25% of human cancers

true

synthesis

when the virus is using the host to make more of themselves.