Infectious particles

what is a virus

what is a virus

obligate intracellular parasites that can only replicate inside host cells

what is a virion

a inert virus that is outside of the host cell

what are the cateogries of viruses

viral class of DNA or RNA

viral genome of ssDNA, dsDNA, ssRNA, or dsRNA

how do viruses get what they need to produce new particles

host cell supplies the building blocks (nucleic acids, amino acids) and machinery (ribosomes)

what are the structures in virions

capsid, nucleocapsid, capsomere, envelope

what is the capsid

protein coat that surrounds the nucleic acid

what is the nucleocapsid

nucleic acid and a protein coat

what is the capsomere

protein subunit that makes up the capsid

what is the envelope

lipid containinglayer with embedded proteins

proteins are virus specific and encoded on the viral genome

used in attachment

what determines the shape of the virus

the nature of the capsomere

what is a helical virus

capsomeres are attached to a virus RNA that loops around is a helix

ex. tabacco mosaic virus

2130 identical capsomeres

what is a polyhedral virus

commonly a icosahedron

capsomere number is determined by geometry

ex. HPV

what is a complex virus

composed of several parts

most complicated in terms of structure are bacteriophages

what are viroids

closed circles of ssRNA

replication depends on host machinery when the disease takes over the machinery

ex. potato spindle fiber

what are prions

consist of one protein

cause neurological degenerative disorders

issue comes from misfolded proteins and the protein cannot replicate

taxonomy of viruses

grouped in families (viridae)

given genus name (virus)

species name usually in english

how are viruses classified

nature of host, type of disease caused, life cycle, naked/enveloped, type of nucleic acid and strandedness

what is the baltimore classification scheme

based on type of genome

indicates replication mechanism

two configurations (plus/minus)

what is plus configuration

RNA genome has the same strand configuration as mRNA and can be translated directly

what is minus configuration

complementary to the mRNA

cannot be read directly, it needs to be converted into the mRNA strand before it can be translated

what is the life cycle of a virus

attachment, penetration, uncoating, replication, maturation, release

what is adsorption

attachment of virus to specific receptors on the cell surface

what is penetration

virus genome enters the cell

what is uncoating

removal of envelope or capsid by host enzymes, sometimes within lysosomes

what happesn to naked viruses in penetration

the genome is expelled from the capsid directly thorugh the cytoplasmic membrane or the entire virion enters the cell

what happens in enveloped viruses in penetration

either fuse with membrane and release genome or use endocytosis (viropexis) and the whole virion enters. then the lysosome degrades the double membrane around the genome

what is maturation

assembly of virus components, nucleic acid, nucleocapsid and accessory proteins to form new virions

usually spontaneous

what is release

mature virions exit the host cell by means of budding or by cuasing lysis of the cell

what are the periods in virus replication

latent (eclipse and maturation)

release (rise)

what is the eclipse period

time for the host cells to replicate the viral genome and to synthesize the viral components

what is the maturation period

time needed for the different components to be assembled

what is the release period

virions are detected outside the cell

lysis - virus encoded proteins damage the cytoplasmic membrane

budding in enveloped viruses

what is the burst size

number of virions released

varies according to many factors

what is budding

the viral capsid enveloped itself in cyotplsmic membrane that has glycoproteins

it then buds out

what is a bacteriophage

most phages contain linear dsRNA genomes

most are naked by might have lipid envelopes

what are the two types of bacteriophages

virulent and temperate (which has two options)

what are virulent phages

infection of host cells always leads to replication, resulting in host cell lysis (lytic pathway)

what are temperature phages (types)

lytic pathway

or lysogenic pathway the genome becomes incorporated into the bacterial host genome

bacteriophage t4

adsorption: t4 attaches to the core region of LPS by the tail fibers

after attachment, tail sheath contracts forcing the central core through outer membrane

lysozymes digest the peptidoglycan layer, forming a small pore

phage DNA is injected into host cytoplasm

lambda replication (temperate)

starts with prolonged latent state of infection (lysogeny)

chart on slides

sometimes, prophage can exit chromosome (excision) and continue along lytic pathway

what is a prophage

phage genome within the host cell chromosome

what is a lysogen

bacterium that contains a prophage

lambda genome

linear dsDNA with cohesive ends

cohesive ends form, and make a circular dsDNA

animal viruses

DNA replication occurs in nucleus

genomes if viral DNA also are replicated in nucelus

genomes of RNA viruses are usuallt replicated in the cytoplasm

there are a list of examples on the slides with a lot of information i think might be easier to learn from there instead of on here…