Viruses, Viroids, and Prions Ch. 13

These flashcards cover key terms and concepts related to viruses, viroids, and prions from the lecture notes.

Virus

An infectious agent that requires a living host cell to replicate and can cause disease. Hijacks host replication machinery. obligate intracellular parasites

Viroid

A small circular RNA molecule that causes disease in plants, causes serious disease

Prion

Infectious agents composed solely of protein, no nucleic acids, linked to neurodegenerative diseases.(transmissible spongiform encephalopathies), resistant to heat and chemical treatments

Bacteriophage

A virus that infects bacteria, often used in genetic research.

Bacteriophage-Lytic phage

Lytic or virulent phages exit host by lysing and killing the cell. T4 Phage infects E.coli

Lysogenic infection

A method of viral replication in which the viral genome integrates into the host genome.

Nucleocapsid

The complex of nucleic acid and protein coat of a virus.

Capsomere

A subunit that makes up the capsid of a virus.

Antigenic drift

The gradual mutation of viruses that can evade the immune system.

Antigenic shift

Major changes in virus antigens can lead to pandemics

Prophage

Viral DNA (phage) integrated into the host cell's chromosome, replicates with host chromosome and is incorporated into cell’s progeny. can remain in a latent state indefinitely

Zoonotic viruses

Viruses that can be transmitted from animals to humans.

Enveloped virus

A type of virus that has an outer lipid membrane.

Non-enveloped virus

A type of virus that lacks an outer lipid membrane and is generally more resistant to disinfectants.

Horizontal gene transfer

The transfer of genetic material between organisms in a manner other than traditional reproduction.

Cytopathic effect

Morphological alterations in host cells due to viral infection.

Plaque assay

using monolayer tissue culture cells, direct count via electron microscopy

Hemagglutination

A process by which viruses induce clumping of red blood cells.

Replication

The process of making copies of the viral genome and proteins within a host cell.

Single-stranded RNA (ssRNA)

A type of viral RNA that can function as mRNA or as a template for mRNA synthesis.

Double-stranded RNA (dsRNA)

Viral RNA made up of two complementary strands.

Iwanowsky & Beijernick

Researchers who discovered viruses. Determined the tobacco mosaic disease. Founders of virology

bacteriophage or phage

is a virus that infects bacteria

Virion (viral structure)

nucleic acid surrounded by a capsid

Capsid

protein coat

Nucleic acid

DNA or RNA, circular or linear, single or double stranded

Giruses

giant viruses

Megaviridae-sputnik

is a viriophage, requires coinfection of host cell with another virus to replicate

3 viral structure shapes

Icosahedral-20 flat triangles, Helical-capsomeres arranged in helix, Complex-(phage) icosahedral (head) and Helical protein (tail)

Virus families end in suffix

Viridae

Enteric viruses

oral-fecal route

respiratory viruses

respiratory route

zoonotic viruses

cause zoonoses (animal to human)

arboviruses (arthropod-borne)

spread by arthropods

Infection cycle-5 steps

attachment, genome entry, synthesis, assembly, and release

Bacteriophage-Attachment

phage attaches to receptors

Bacteriophage-Genome entry

phage injects genome into cell, capsid remains outside cell

Bacteriophage-Synthesis

viral proteins translated, nuclease degrades host DNA, phage dna replicated

Bacteriophage-Assembly

maturation, new phage particles are assembled from synthesized proteins and replicated DNA, then packaged into capsids.

Bacteriophage-Release

Lysozyme digest cell wall of bacterium, cell lyses and releases phages

Lambda

best studied temperate phage, infects E.coli, two options for infection: lytic infection or Lysogenic infection

integrase

phage encoded enzyme that integrates viral DNA into the host genome.

lysogen

bacterial cell carrying prophage

Why are most prophage genes silent

A phage encoded repressor protein prevents expression

Phage excision

can be induced by a DNA damaging agent such as ultraviolet light

Protease

destroys repressor, allows prophage genome to be excised and enter lytic cycle

phage induction

allows phage to escape a damaged host

lysogenic conversion

lysogenic bacterium may show change in phenotype due to the presence of prophage DNA

Toxins

encoded by phage genes may cause virulence of bacterial pathogens

HUS (Hemolytic uremic syndrome)

blood vessel damage causes clots that lead to kidney damage

S.pyogenes

causes toxic shock due to phage encoded “super antigen” which inappropriately activates T-cells of the immune system

Generalized transduction

results from packaging errors during phage assembly, degraded host chromosome fragments are mistakenly packaged into phage heads

specialized transduction

excision mistake, during transition from lysogenic to lytic cycle of temperate phage, only adjacent genes to phage DNA are packaged

Animal virus replication

virally encoded enzymes are target of antiviral drugs, antiviral meds can slow progression of viral infection, gives host immune system time to eliminate virus before illness occurs

Animal virus replication-Attachment

Adsorption- virus attachment protiens (spikes) bind to receptor on host cell surface. Enveloped viruses:enter by fusion or endocytosis, non-enveloped viruses: can not fuseand must enter by endocytosis

uncoating

The process during viral replication where the viral capsid is removed, allowing the viral genome to enter the host cell's cytoplasm.

Animal virus replication-Synthesis

The stage in viral replication where the host cell's machinery is hijacked to produce viral proteins and replicate the viral genome.

Replication of DNA viruses

occurs in cell’s nucleus, DNA replicated to form viral genome, transcribed to produce mRNA which is then translated into viral proteins

Replication of RNA viruses

replication occurs in the cytoplasm, require virally encoded RNA-dependent RNA polymerase to synthesize complementary RNA strands and produce viral proteins.

purpose of a virus

to make protein and genome copies

RNA replication faults

lack proofreading ability, generates mutations during replication, results in antigenic variations called antigenic drifts

Influenza

RNA viruses with segmented genomes

RNA Transcribing viruses (reverse)

encode enzyme reverse transcriptase to make DNA from RNA, Retroviruses (HIV)

Animal virus replication-Assembly

maturation, nucleic acid packaged into capsid to form nucleocapsid

Animal virus replication-Release

enveloped viruses-leave via budding, non-enveloped viruses-releases when host cell dies, often by apoptosis

Acute infections

immune system eliminates

persistent infections

yrs. or lifetime (HIV), may be chronic or latent (VSV & HSV-1)

Cytopathic effect of viral replication

distinct morphological alterations

inclusion body

site of viral replication

Quantal assay

dilution of virus given to host, Titer dilution-50% infective, 50% lethal

Plant viruses

generally do not recoverfrom infection, leading to growth abnormalities and wilting.