Viruses (3.3)

•Lysogenic conversion

"acquisition of new properties by a host cell infected by a lysogenic phage"

•Lysogeny:

"state in which phage DNA is incorporated into the host cell without lysis

Characterize the nucleic acids found in viruses.

-All contain nucleic acid, DNA or RNA (but not both), & a protein coat, which encases the nucleic acid. -Double-stranded (ds) or single-stranded (ss) -Linear or circular

Describe the general structure of viruses, including: capsid, capsomere, nucleic acid, envelope, spikes.

-Has a capsid, a protein coat that protects t/ nucleic acid. It's made of structural subunits called Capsomeres (1 or several kinds of caps) -Can be host range determinant -May contain spikes - protein/carbohydrate complex

Describe methods for laboratory culture of viruses.

-Living animals - some can only be cultured here -Embryonated eggs - vaccine development / manufacture, egg membranes mimic culture monolayers -Cell cultures - a single layer of cells (monolyer) forms, virus is added & infects cells, virus detected because cell lyses and plaque forms.

List and describe the steps in the multiplication of a lytic, double-stranded DNA, T-even bacteriophage.

1 Attachment: Phage attaches by tail fibers to host cell 2 Penetration: Phage lysozyme opens cell wall; tail sheath contracts to force tail core & DNA (phage) into cell 3 Biosynthesis: Production of phage DNA & proteins 4 Maturation: Assembly of phage particles 5 Release: Phage lysozyme breaks cell wall

Describe the lysogenic cycle of bacteriophage lambda.

1 Phage attaches to host cell & injects DNA 2 Phage DNA circularizes & enters lytic cycle or lysogenic cycle 3 Phage DNA integrates w/in the bacterial chromosome by recombination becoming a prophage 4 Lysogenic bacterium reproduces normally 5 The prophage may excise from the bacterial chromosome by another recombination event, initiating a lytic cycle

Describe the seven events in the multiplication of a DNA-containing virus, e.g. Papovavirus.

1. Attachment - virus attaches to cell membrane - virus host range determinants (i.e. spikes) bind receptors on host membrane 2. Entry and Uncoating (cytoplasm) - entry - pinocytosis (endocytosis) or fusion- uncoating & release of viral DNA into host nucleus 3. Early viral protein synthesis (nucleus)- transcription - by viral or host enzymes- translation - by host ribosomes 4. Biosynthesis of Genome (nucleus)- DNA replication; synthesis of some viral proteins 5. Late viral protein synthesis -(cytoplasm) capsid proteins are made in cytyplasm and migrate to nucleus 6. Maturation: (nucleus) -- viral genome & capsid proteins assemble in the nucleus to produce mature capsid 7. Release:- budding - enveloped viruses- rupture - non-enveloped viruses

Viral species:

A group of viruses sharing the same genetic information & ecological niche (host).

Name two factors that determine the host range of a phage.

A host range is the cell that the virus infects. Viruses usually species-specific & in multicellular organisms, infecting specific cell types (nerve, skin, liver, blood cells, etc.) Host range is determined by both the host & virus: 1. specific molecules of the host allowing attachment (attachment sites) 2. specific virus proteins involved in attachment 3. presence of cellular proteins for viral replication.

Define, Describe, and explain bacteriophage (aka Phage)

A virus that infects bacteria - tend to be bacterial species-specific (bacteriophage that infect E. coli cannot infect P. aerogenes) • Host range: Adsorption - irreversible attachment of phage to host surface - phage has absorption site that is chemically complementary to specific receptor on host. • Host receptors on lipoprotein outer layer of cell wall, lipopolysaccharide layer, cell appendages • Phage adsorption sites on capsid or tail fibers • Must be cultured using growing bacterial cultures

Compare the size of animal viruses to prokaryotic and eukaryotic cells.

Animal viruses are much much smaller (a few 100nm compared to 1000s of nm)

Compare viruses to bacteria

Bacteria are single-celled, prokaryotic microorganisms that exist in abundance in both living hosts and in all areas of the planet (e.g., soil, water). By their nature, they can be either "good" (beneficial) or "bad" (harmful) for the health of plants, humans, and other animals that come into contact with them. A virus is acellular (has no cell structure) and requires a living host to survive; it causes illness in its host, which causes an immune response. Bacteria are alive, while scientists are not yet sure if viruses are living or nonliving; in general, they are considered to be nonliving.

Multiplication of Bacteriophage

Bacteriophage are viruses of bacteria •No envelope •Capsid - most are polyhedral or filamentous (helical), simple and complex •Genomes: -dsDNA, ssDNA, dsRNA, ssRNA •Can replicate using one of two replication cycles (pathways); lytic and lysogenic

•Lysogenic phage:

Bacteriophage capable of undergoing lysogeny (a/k/a: temperate phage; latent phage)

Describe cytopathic effects of viral infections

Change in cell morphology, cell deterioration, or even cell death; can cause plaques in cell culture monolayers, similar to plaques caused by bacteriophage

Cytopathic Effect (definition)

Changes in cell (morphology, cell deterioration) due to infection of cell

Define, Describe, and explain virion

Complete, fully developed, infectious viral particle - vehicle of transmission between hosts •Nucleic acid genome -DNA or RNA •Capsid •Envelope (optional) •Spikes (optional)

Example of Virus nomenclature

Example: •Order: Herpesvirales •Family: Herpesviridae •Genus: Simplexvirus, •Species: Human herpesvirus •Sub-species: Human herpesvirus 2

Describe some viral shapes.

Helical (hollow cylindrical capsid) or polyhedral (many sided - icosahedral meaning 20 sides w/ 12 corners)

•Lysogenic cell (lysogen):

Host carrying a prophage

Compare viruses to bacteria (Chart)

Intracellular Parasite (B)No (V)Yes Plasma Membrane (B)Yes (V)No Binary Fission (B)Yes (V)No Pass through biological filters (B)No (V)Yes Can have a RNA genome (B)No (V)Yes ATP-generating metabolism (B)Yes (V)No Ribosomes (B) Yes (V)No Sensitive to Antibiotics (B)Yes (V)No Sensitive to Interferon (B)No (Y)Yes

What is Lysogeny

Lysogeny, or the lysogenic cycle, is one of two cycles of viral reproduction (the lytic cycle being the other). Characterized by integration of the bacteriophage nucleic acid into the host bacterium's genome or formations of a circular replicon in the bacterial cytoplasm.

Bacteriophage Replication (2 cycles)

Lytic cycle (causing lysis & death) Lysogenic cycle -Infected host cell does not die and lyse immediately but persists for several generations -When the host cells begin to die due to lack of nutrients or physical damage (e.g. UV light) the prophage initiates viral replication and begins the lytic cycle.

Describe naked virus

Naked viruses: lack a lipid envelope •Bacteriophage (prokaryotic viruses) are naked. •Eukaryotic viruses (viruses of eukaryotic cells) can be either naked or enveloped •In naked viruses capsid proteins determine host range •Tend to survive longer in environment

Define, Describe, and explain burst size

Number of bacteriophage, or virus, produced within an infected cel

Define, Describe, & explain plaque and plaque-forming unit (PFU)

Plaque - clear area in bacterial lawn formed by lysis of infected bacteria -Plaque method detects & counts bacteriophage - Plaque forming units (PFU) -Bacteriophages can also be propagated using bacterial cultures in liquid media.

Define, Describe, and explain prion

Proteinaceous Infectious particle•Cause disease without nucleic acid genome•Prion converts normal brain protein into prion•Prions accumulate in brain causing plaques•Inherited and transmissible by ingestion, transplant, and surgical instruments -Spongiform encephalopathies (i. e. brain damage): Sheep scrapie, Creutzfeldt-Jakob disease (CJD), Gerstmann-Sträussler-Scheinker syndrome (GSS), fatal familial insomnia, mad cow disease

Define, Describe, and explain provirus

Prt of Retrovirus -- HIV - Provirus stage -integration of ds DNA viral genome into host genome.

RNA Virus Replication

RNA viruses are grouped depending on the type of RNA in the capsid I. (-) RNA strand viruses II. (+) RNA strand viruses III. (+) RNA strand viruses with segmented, non- overlapping genome) IV. dsRNA viruses with segmented, non-overlapping genome V. retroviruses

Characterize viruses as pathogens.

They're obligatory intracellular parasites, needing host's metabolism to reproduce. They're Acellular (not a cell) & "non-living" Infected cell is the "host" cell •Eukaryotic virus infects eukaryotes •Prokaryotic virus - (bacteriophage) infects prokaryotes

Recall transduction and the role of phages in gene transfer.

Transduction is the process by which foreign DNA is introduced into a cell by a virus or viral vector. An example is the viral transfer of DNA from one bacterium to another. ... Transduction is a common tool used by molecular biologists to stably introduce a foreign gene into a host cell's genome.

Describe Enveloped Viruses

Viral envelopes are unique to eukaryotic viruses, but not all eukaryotic viruses are enveloped (i.e. see naked virus slide) •Lipid bilayer derived from host cell membranes; usually plasma or nuclear membranes •Can contain viral & host proteins and also carbohydrates •May contain spikes

In its infective form, outside the cell, a virus particle is called a virion

Virion is the transport vehicle name

Bacteriophage

Viruses of bacteria

Define, Describe, and explain reverse transcriptase

reverse transcriptase (RT) is an enzyme used to generate complementary DNA (cDNA) from an RNA template, a process termed reverse transcription. It is mainly associated with retroviruses.

Prophage

the phage genome after insertion into host chromosome

Define, Describe, and explain genome

•DNA or RNA genomes •Double-strnded (ds) or single-strnded (ss) genomes •Linear or circular genome

Criteria used to identify viruses

•Host range •Virion Structure - capsid shape, envelope or naked, nucleic acid, etc. •Cytopathic effects -changes in host cell caused by viral infection •Serological tests -Use of antibodies that bind species-specific molecules

Describe criteria used to classify and name viruses (nomenclature).

•Order ends in -ales •Family ends in -viridae. •Genus ends in -virus. (italics, first letter capital) •Species names are descriptive (common names used for species & may be abbreviated) •Subspecies designated with a number••

Lysogeny Terminology

•Prophage: the phage genome after insertion into host chromosome •Lysogeny: "state in which phage DNA is incorporated into the host cell without lysis •Lysogenic phage: Bacteriophage capable of undergoing lysogeny (a/k/a: temperate phage; latent phage) •Lysogenic cell (lysogen): Host carrying a prophage •Lysogenic conversion: "acquisition of new properties by a host cell infected by a lysogenic phage"