M4 - Virology Flashcards
Characteristics of a virus
• Intracellular parasite
– Cannot replicate outside a living cell
– Large inert macromolecules
• Possess only one kind of nucleic acid: DNA or RNA
• Limited amount of genetic material: ~3-200 genes
• cannot code for energy production due to not enough genetic info
• no ribosomes
• not grow but replicate to increase the number
• Viral nucleic acid and viral protein synthesis occur separately: come together during maturation.
• Lipids and carbohydrates are acquired from the host cell (not coded for by viral genome)
Composition of a virus
a nucleic acid genome (RNA or DNA) + protein
Virus proteins are coded by …
viral genome or from host
particle (virion)
病毒顆粒（病毒粒子）
penetration
滲透
polymerases
聚合酶
helicases
解旋酶
proteases
蛋白酶
Structural proteins
part of the virus particle (virion) and wrapping around the core of viruses
Functions of structural proteins
cell attachment and penetration & protection
Location & functions of Non-structural proteins
most not found in virion
– replication(polymerases,helicases)
– virus assembly and release (proteases)
Nucleocapsid
核衣殼 = capsid(protein shell surrounding viral genome) + genome
Capsid
衣殼
protein shell surrounding viral genome
capsomer
衣殼粒a kind of structural proteins
Many capsomers make capsids
Icosahedral
二十面體
spherical
球體
Helical Nucleocapsids
螺旋核衣殼
Rod-shaped
桿狀
naked viruses
Viruses composed only of nucleic acid and protein
enveloped viruses
Viruses that acquire an outer layer of membrane from the host during replication
Feature of naked virus
- very stable in the environment
- nucleic acid “encased” in protein
Feature of Enveloped viruses
• more fragile 脆弱
• more susceptible to inactivation because of lipid content
naked helical viruses only found in…
plant and bacterial viruses
Complex Viruses
Large viruses with complex structure
How do viruses acquire an envelope?
The virus acquires the envelope as it matures and buds through the cell membrane
What factors determine the structure of a virus
- Types of viruses
- Type of Nucleic Acid: DNA or RNA
- Capsid protein: The composition and arrangement of the capsid protein affect the appearance of the virus.
- Have envelope or not
Stages of replication
- absorption/attachment
- Penetration
- uncoating
- replication
- release/maturation
Virus attachment sites
Enveloped viruses: spike or peplomers
Naked viruses: anywhere
spike
尖峰
peplomers
聚合物
The way of Attachment
– physical complementarity between virus and receptor
– specific interaction (most viruses can only infect some cell types)
PENETRATION
內吞作用
virus is engulfed into cytoplasmic vacuole
The ways of penetration
- Endocytosis
- Membrane fusion: only enveloped viruses
- Direct entry: some naked viruses
The ways of penetration for naked viruses
- direct entry: The nucleocapsid undergoes molecular rearrangement allowing viral genome to enter the cell.
- Exosomes: Naked viruses are excreted from infected cells in exosomes and enter new cells in membrane-bound particles
Un-coating
allows release of the genome into the cytoplasm - Often spontaneous自發性的
Synthesis of viral protein and nucleic acid for DNA viruses
Replicate in the cell nucleus
because all DNA replicative enzymes are found in the nucleus
Synthesis of viral protein and nucleic acid for RNA viruses
Generally replicating in the cytoplasm
RNA viruses code for replicative enzymes (proteins) but need polyribosomes to translate them from mRNA
Replication of negative (-) strand genome
- Negative strand genomic RNA released into the cytoplasm
- The replicase enzymes are brought into the cell as part of the virion
- Negative (-) strand RNA must first serve as a template to make complementary positive (+) strand RNA to translate viral proteins.
Virus maturation and release
simple viruses: self-assembly
complex viruses: require various stages
Maturation and release of viruses for naked viruses
Mainly, accumulate累積 in cell and release progeny子代 virus suddenly through cell bursted破裂
but some progeny viruses are secreted gradually from intact cell in exosomes
exosomes
外泌體
progeny
子代
Maturation and release of viruses for Enveloped viruses
bud through cell membrane – released gradually
Three types of targets for Antiviral Agents
Protein synthesis
Cellular enzymes for DNA replication (for DNA viruses)
Cellular energy to drive synthesis and enzyme reactions
necrosis
壞死：cell death by rupture of cell during virus release
apoptosis
細胞凋亡cell commits suicide in response to infection
Immunopathology
免疫病理學
What causes the symptoms of virus infection?
1) Damage to cells due to virus replication: necrosis壞死, apoptosis細胞凋零 ＆ infected cell loses function
2) Damage due to the host response to infection: Immunopathology, fever, inflammation
pathogenesis
發病機制
HOST factors which modify viral pathogenesis
- Age
- Genetics
- Metabolic state
- “Altered” immune responses: genetically determined, consequence of infection & iatrogenically (therapeutically)
iatrogenically
醫源性
Routes of virus entry
- skin
- respiratory tract
- gastrointestinal tract
- genitourinary tract
- conjunctiva
gastrointestinal tract
胃腸道
genitourinary tract
泌尿生殖道
conjunctiva
結膜
how virus get into host through skin
- mechanical trauma
- by injection
- by the bite of an infected sth
how virus get into host through Genitourinary Tract
Tears or abrasions擦傷
abrasions
擦傷
