MID 2 - Lecture 9 Flashcards
Virus
Small, Infectious agent
Can only replicate within host organism, cannot reproduce (> 1 molecule)
Bacteriophages
bacterial viruses, many infect euk hosts, classified into families based on genome struc, life cycle, etc)
Virion
Virus particle, size 10-400 nm, contain nucleocapsid, can be non-enveloped, or enveloped
Capsids
Large, protect viral genetic material, helps with transport, made of promoters
Helical capsids
Hollow tubes with protein walls, self assemble, size is function of nucleic acid
Icosahedral capsid
Many viruses have, regular polyhedron (20 faces)
Capsid with complex symmetry
Don’t fit category (poxviruses, large bacteriophages)
Viral envelopes
Many viruses bound by envelope
Viral envelope proteins
Spikes, used for identification of virus, viral attachment, enzymatic/other activity, role in nucleic acid replication
Virulent phage
one reproductive choice (multiples immediately upon entry, lyses bacterial host cell) LYTIC ONLY
Temperate phage
2 reproductive options (lytically, or remain within host cell without destroying it)
LYTIC OR LYSOGENIC
Lytic cycle and lysogenic cycle
look at picture
Viral genome
diverse array of genomes, virus may have single/double stranded DNA or RNA, length of nucleic acid varies (4000, 2 mill bps), linear, circular or segmented
Virus classification (OG)
Nucleic acid type, presence or absence of envelope, capsid symmetry, dimensions of virion and capsid
Alternative classification scheme
7 groups
1. dsDNA 2. ssDNA 3. dsRNA 4. + strand ssRNA 5. - strand ssRNA 6. retroviruses 7. reverse-transcribing DNA viruses
dsDNA viruses
largest, most bacteriophages have, important vertebrate viruses, rely on host’s DNA/RNA polymerase
Bacteriophage T4 (3 steps)
Virulent dsDNA phage
steps:
1. adsoprtion to receptor on E.coli outer membrane
2. Tail sheath lysosome/central tube pierce the cell wall
3. Viral nucleic acid is injected into host cell through tube
Life cycle of bacteriophage T4
Early mRNA transcrip, host DNA degrad, Phage DNA repl, late RNA transc, head and tails synthe, genome packing, virion assembly, host cell lysis
Bacteriophage lambda
Phage lambda can enter either the lytic or lysogenic cycle upon infection of e.coli (lyso- dsDNA become prophage)
Reproduction of RNA phages
RNA genome don’t rely on host cell enzymes for replication/ mRNA synthesis
RNA- dependent RNA polymerase completes life cycle
Plus strand RNA viruses
Used for protein synthesis, replicate in cytoplasm, synthesize RNA depen- RNA polymerase (SARS-CoV-2)
Negative strand RNA viruses
preformed RNA-dependent RNA polymerase, new plus strand intermediates synthesized, new + strand serves as template for genome synthesis
Retroviruses
convert ssRNA into dsDNA using reverse transcriptase dsDNA integrates into host cell genome, HIV
Viral multiplication
attachement, entry and uncoating of genome, synthesis, assembly, virion release
Viral entry (3 methods)
- Fusion of viral envelope with host membrane
- Endocytosis in vesicle
- Injection of nucleic acid
Naked - Endocytosis, inject nucleic acid
Enveloped virus - attachement to receptors with spikes, fusion or endocytosis
Animal virus entry mechanisms
a) enveloped virus: fusion with plasma membrane
b) enveloped virus: endocytosis (escape into cytoplasm)
c) naked virus: endocytosis - nucleic acid extruded
Virion release (influenza)
budding, viral proteins in host membrane, nucleocapsid may bind to viral proteins, envelope derived from host cell membrane
Infection in eukaryotic cells
cytocidal infection = cell death through lysis
Cytopathic effects = degenerative changes, abnormalities
