Chapter 13 Flashcards
What are some general characteristics of viruses?
- Obligatory intracellular parasites (require living host cells to multiple)
- Contain DNA or RNA
- Contain a protein coat
- No ribosomes
- No ATP-generating mechanism
What is a host range?
- The spectrum of host cells a virus can infect
- Most viruses infect only specific types of cells in one host (determined by specific host attachment sites and cellular factors)
- Bacteriophages
- Range from 20 nm to 1000 nm in length
Bacteriophage
viruses that infect bacteria
Viral Structure
Viron - complete, fully developed viral particle
- nucleic acid
- Capsid
- Envelope
- Spikes
Describe the viral structures of DNA/RNA
DNA or RNA can be single or double stranded; linear or circular
Capsid
Part of the viral structure;
Protein coat made of capsomeres (subunits)
Describe the viral structure of the envelope
lipid, protein, and carbohydrate coating on some viruses
Describe spikes and their viral structure
projections from outer surface
General morphology of viruses includes what 4 types?
- Helical virus - hollow, cylindrical capsid
- Polyhedral viruses - many-sided
- Enveloped viruses - lipid, protein coating
- Complex viruses - complicated structures
Taxonomy of Viruses:
- Genus names end in _____
- Family names end in _____
- Order names in end _____
- -virus
- -viridae
- -ales
Viral Species
- a group of viruses sharing the same genetic information and ecological niche (host)
- Descriptive common names are used for species
- Subspecies are designated by a number
Viruses must be grown in ______ cells.
living
Bacteriophages are grown in bacteria.
Bacteriophages form ________, which are what?
Each ________ corresponds to a single ______ and can be expressed as _______.
plaques
plaque, virus; plaque-forming units (PFU)
What are three main ways of growing animal virusesin the laboratory?
- In living animals
- In embryonated eggs
- In cell cultures
What happens when you grow an animal virus in an embryonated egg?
- The vrus is injected into the egg
- The viral growth is signaled by changes or death of the embryo
What happens when animal viruses are grown in cell cultures?
- Tissues are treated with enzymes to separate cells
- Virally infected cells are detected via their deterioration, known as the cytopathic effect (CPE)
- Continuous cell lines are used
T/F
Viruses are acellular
True
Viruses do/do not use binomial nomenclature
Do not
Virion
Complete, fully developed viral particle.
T/F
Nucleic acid - DNA or RNA in viruses can be single or double stranded
True
Capsid
Protein coat made of capsomeres
Capsomeres
Subunits of the capsid protein coat
Envelope
lipid, protein, and carbohydrate coating on some viruses
Spikes
projections from the outer surface of the envelope of a virion
Can you draw the structure of a virion? How would you describe it? How would you describe its DNA/RNA?
Remember these main structures: capsid (capsomeres), envelope, spikes, the DNA or RNA can be either single or double stranded
Helical viruses
Viruses that have a hollow, cylindical capsid
How would you describe/draw the structure of a polyhedral virus?
Many sided
How would you describe the structure of an enveloped virus?
A protein, lipid, and carbohydrate structure surrounding a capsid which holds a virus
How would you describe complex structures of viruses?
Generally complicated. A good example is a bacteriophage (pictured).
Viral species
a group of viruses sharing the same genetic information and ecological niche (host)
Descriptive common names are used for species
Subspecies are designated by a number
What kind of cells must viruses be grown in?
living
What types of cells are bacteriophages grown in?
bacteria
plaques
Bacteriophages form placques, which are clearings on a lawn of bacteria on the surface of agar
Each plaque corresponds to a single virus; can be expressed as plaque-forming units (PFU)
What are three different ways that animal viruses can be grown in labs?
Living animals
Embryonated eggs
In cell cultures
What is the indicatio of viral growth in embryonated eggs?
Viral growth is signaled by changes or death of the embryo.
Cytopathic effect (CPE)
Virally infected cells are detected via their deterioration
Continuous Cell Lines
Cells that have acquired the capacity for infinite growth and division
Usually derived from tumor cells or transplanted cells (cells that become resistant to factors associated with growth control, produce cancer in animals)
How are viruses identified?
- Cytopathic effects
- Serological testing
- Western blotting - reaction of the virus with antibodies
- Nucleic acids
- RFLPs
- PCR
RFLP
Restriction Fragment Length Polymorphism
DNA profiling technique
What two things must a virus have to multiply?
- It must invade a host cell
- It must take over the host’s metabolic machinery
Sketch a one-step growth curve graph
Explain the decrease and increase of growth in the graph
Initial decrease: Virus has entered cell, but no progeny virions are created yet.
Steady increase: virions are being created
Decrease: cell death results in virions being released
Lytic cycle
Bacteriophage multiplication in which phage causes lysis and death of the host cell
Lysogenic Cycle
- Phage DNA is incorporated in the host DNA
- Phage conversion
- Specialized transduction
Specialized transduction
- Bacterial genes can be picked up in a phage coat and transferred to another bacterium in a process called generalized transduction
- Changes genetic properties of the bacteria
What are the five steps of the Lytic cycle?
- Attachment: phage attaches by the tail fibers to the host cell
- Penetration: phage lysozyme opens the cell wall; tail sheath contracts to force the tail core and DNA into the cell
- Biosynthesis: production of phage DNA and proteins
- Maturation: assembly of phage particles
- Release: phage lysozyme breaks the cell wall
Lysogeny
Phage remains latent
Lysogenic cycle
- Phage DNA incorporates into host cell DNA
- Inserted phage DNA is known as prophage
- When the host cell replicates its chromosome, it also replicates prophage DNA
- Results in phage conversion - the host cell exhibits new properties
Phage conversion
Host cell exhibits new properties
Steps of multiplication of animal viruses
- Attachment: viruses attach to the cell membrane
- Entry by receptor-mediated endocytosis or fusion
- Uncoating by viral or host enzymes
- Biosynthesis: production of nucleic acid and proteins
- Maturation: nucleic acid and capsid proteins assemble
- Release by budding (enveloped viruses) or rupture
Where is DNA of a virus replicated in a host cell?
Where are capsids synthesized?
DNA is replicated in the host’s nucleus
Capsids are synthesized in the cytoplasm using the host cell enzymes
Characteristics of picornaviridae
Single stranded RNA, + strand, nonenveloped
Name a few RNA viruses and what family they belong to
- Family: Picornaviridae
- Single stranded RNA, + strand, nonenveloped
- Enterovirus
- Poliovirus and coxsackievirus
- Rhinovirus
- Common cold
- Hepatitis A virus
- Enterovirus
- Single stranded RNA, + strand, nonenveloped
T/F
Viral cancers are contagious
False
