Viruses Flashcards
What is a virus?
A virus is a non-cellular particle that must infect a host cell to reproduce
Viruses
– are obligatory _________ __________
– that take over the _______ _______ ______ and direct the cell to produce more virus particles.
- obligatory intracellular parasites
– the infected cell’s machinery
A virus particle (______), consists of nucleus acid (___ or ___) contained within a protective coat called a _______
What do they not contain?
- Virion
-DNA or RNA
-capsid
-do not contain ribosomes or ATP generating machinery
What are the 6 general characteristics of viruses?
- Most viruses are very small
- Viruses contain nucleic acid (DNA or RNA)
- Nucleic acid is packaged in a protein coat (capsid)
- Some viruses are enclosed in an envelope
- Some viruses have spikes
- Each species of virus infects a particular group of host species, called the host range
What size is most viruses?
50-100 nm
Nucleic acid can be:
• DNA or RNA
• Single or double-stranded
• Circular or linear
The virus “genome” is usually very small and usually encodes only a few genes.
Name these 3 genes:
• Capsomere (capsid subunits)
• Envelope proteins (if enveloped virus)
• Polymerase (if special polymerase needed)
How many protein coding genes does Influenza A virus have?
11 coding genes
The nucleic acid is packaged in a protein coat called the _____
Capsid
Capsid is made of repeating protein subunits called _______. What do they do?
•capsomeres
• package and protect viral genome
Some viruses are enclosed in an envelope. What is an envelope?
bilayer that surrounding capsid, derived from the host cell membrane
What are enveloped viruses more sensitive to?
Heat or detergents
Virus have spikes. What are spikes? What are they involved in?
• The spikes are glycoproteins (carbohydrate-protein complexes) in the envelope.
• Spikes are involved in attachment to a host cell and escape from a host cell
Each species of virus infects a particular set of host’s. What can they infect?
• Bacteria
• Fungi
• Protozoa
• Plants
• Animals
Most viruses can only infect a specific type of cells within a single host species
What does the HIV virus infect?
HIV (virus) infects T cells (cell type) in humans (host species)
(Define)
- Host Range:
- Tissue tropism:
• Host range: set of species that a particular virus can infect
• Tissue tropism: tissue and/or cell type that virus can infect
Host range and tissue tropism are generally determined by what?
specific host attachment sites on the virus (spikes) and the presence of specific receptors on the host cell
There are 5 steps of Viral Replication (Viral Life Cycles)
What are the steps and give a small description of them:
- recognition/ attachment
• Viruses must contact and adhere to a host cell that can support replication of specific virus - entry
• The viral genome must enter the host cell and gain access to the host cell’s machinery for gene expression - Biosynthesis
• Includes synthesis of both viral genome and virus-specific proteins - Assembly of virions
• Components usually self-assemble spontaneously. - Exit and transmission
• Progeny virions must exit the host cell and reach new host cells and, if multicellular, new hosts to infect
Bacteriophage are viruses that infect bacteria. What kind of temperatures do they withstand? What shape do they have?
They are mostly mesophilic and mildly thermophilic.
Icosahedral head-filamentous tail shape
What are the 5 steps of the lytic cycle of a bacteriophage (Describe each briefly)
- Attachment: Phage attaches to host cell
- Penetration: Phage penetrates and inserts DNA into host cell
- Biosynthesis: Production of phage DNA and phage proteins by the infected cell
- Maturation: Self-assembly of phage particles; virus genome is packaged into capsid
- Release: Phage degrades infected host cell wall; host cell lyses (bursts); new phage particles are released
Define transduction
Transduction is the transfer of DNA from one bacterial cell to another bacterial cell by a bacteriophage
Generalized transduction involves the ______ life cycle of the phage and can move any _____
Lytic life cycle
Gene
(Define)
Virulent phage:
Temperate phage:
• Virulent phage: reproduce only through the lytic cycle, resulting in lysis of the host bacterial cell
– Ex: phage T4
• Temperate phage: can reproduce through the lytic cycle; can also undergo lysogeny, where the phage genome inserts into the host genome
– Ex: phage lambda
What are the 5 steps of the Lysogenic Cycle of a bacteriophage? (Give brief description of each)
- Attachment: Phage attaches to host cell
- Penetration: Phage inserts DNA into host cell
- Integration: Phage DNA integrates into bacterial chromosome by recombination; the integrated phage DNA is called a prophage
– expression of phage genes is repressed
– “lysogenic bacterium” divides normally; prophage is maintained in the
bacterial chromosome
-Phage may carry genes that give host cell an advantage - Excision: Prophage excises from chromosome (phage induction); excision can be stimulated by UV or chemical
- Lytic cycle: Excised phage enters lytic cycle
