Module 4: Basic Characteristics of Viruses Flashcards
What is a virus?
Microscopic, acellular agent composed of nucleic acid surrounded by a protein coat
Obligate Intracellular Parasite
cannot multiply unless they invade a specific host cell and instruct its genetic and metabolic machinery to make and release quantities new virus
Properties of Viruses
- nucleic acid can be either DNA or RNA, but not both
- nucleic acid can be double or single stranded
- molecules of virus surface give them high specificity for attachment to host cell
- lack enzymes for most metabolic processes
- lack machinery for synthesizing proteins
Virus Structure
- all viruses have a protein capsid which surrounds the nucleic acid (capsid + nucleic acid = nucleocapsid)
- may have an additional envelope
- has spikes
What are spikes on a virus?
- proteins that project from outer surface
- allow viruses to dock on their target host cell
Naked vs Enveloped Virus
Naked has no envelope while enveloped has one
Viral Capsid
- formed of identical subunits (capsomers)
- spontaneously self-assemble
- two shapes: helical or icosahedral
Helical Capsid
- simpler
- rod-shaped
Icosahedral Capsid
- can have more than one type of capsomer
Viral Envelope
- acquired when viruses are released from the host cell
Genome
- the total genetic information carried by an organism
- contained the “code” to make new viruses
Central Dogma
- encodes proteins
- DNA -> RNA -> Protein
DNA transcription -> RNA (mRNA, translation) -> Protein function
What are the animal virus replication steps?
- adsorption
- penetration and uncoating
- synthesis
- assembly
- release
Adsorption
virus spikes attaches to host cell via specific receptors on the host cell
Penetration and Uncoating
endocytosis
fusion of envelope
Endocytosis
Entire virus is engulfed and enclosed in a vacuole or vesicle. Enzymes dissolve the envelope and capsid. Viral nucleic acid is released.
Fusion of viral envelope with hose cell membrane
envelope merges directly with the cell membrane releasing the nucleocapsid into the cell’s interior
Synthesis
part of virus are synthesized and nucleic acid replicates
Know how different genomes are replicated
look at slide 21-27
Assembly
mature virus particles are constructed
Release
cell is lysed or virus is budded out
Bacteriophage (Phage)
virus that specifically infects bacteria
Lysogeny
- Phage DNA is interred into bacterial DNA
- viral DNA is retained by bacteria cell and copied during normal cell division
- induction
Induction
process by which the prophage in a lysogenic cycle will be activated
Lysogenic Conversion
cause the production of toxins/enzymes which harm the human
Cultivation of Viruses - Why?
- isolate and identify viruses in clinical specimens
- prepare viruses for vaccines
- do detailed research on viral structure, multiplication cycles, genetics, and effects on host
Cultivation of Viruses - How?
- live animal inoculation (exposed by injection)
- bird embryos (intact and self-supporting unit, sterile environment and nutrients, embryonic tissue support viral multiplication)
- cell (tissue) culture techniques (cells grow to form a monolayer that supports viral multiplication)
Viral Treatment
- inhibition of virus entry
- inhibition of nucleic acid synthesis
- inhibition of viral assembly/release
