CH 13 Flashcards
What are viruses?
nucleic acid with a protein shell and a lipid-containing membrane
Where do viruses replicate
only in living host cells
What do other microorganisms have that VIRUSES DO NOT (3)
- cell membrane
- cytosol
- organelles
What do you call viruses that infect and replicate in only bacterial cells
bacteriophages
How do viruses create more viral molecules, nucleic acid, and proteins?
by infecting and using the metabolic machines of other bacteria
What do you call a virus @ an extracellular state?
virion (cant reproduce and is inactive)
PARTS of a virion
IF NAKED VIRUSES:
- Nucleocapsid
- capsid (protein shell that aids in attachment to host and for protection)
- nucleic acid core (houses the nucleic acid) - Viral genome (nucleic acid)
IF ENVELOPED VIRUSES:
3. Envelope (phospholipid membrane)
Where do enveloped viruses get their envelope
from the host cell
What happens upon a virion entering a host cell?
Capsid and envelope disintegrates -> virus becomes active and exists solely as nucleic acid
What are capsomeres? (definition + arrangement)
- protein/capsid sub-units
- arranged in a highly repetitive manner around the nucleic acid
3 viral symmetries
- Helical
- Icosahedral
- Complex
HELICAL SYMMETRY
- shape
- additional part
- disc-shaped
- central cavity
ICOSAHEDRAL SYMMETRY
- shape
20 triangle faces + 12 vertices
COMPLEX SYMMETRY
- shape
- icosahedral head
- helical tail (sheath)
NUCLEIC ACID in VIRUSES
- type
- shape
- # of strands
- segmentation
- DNA or RNA
- linear or circular
- single / double stranded
- segmented / non segmented
6 functions of PROTEINS in viruses
- protection against inactivation by nucleases
- participate in attachment to host
- facilitate transfer of viral NA from 1 host cell to another
- initiation of virus replication
- provide structural symmetry
- determine antigenic property
Where can lipids be found in viruses
In envelopes from the host cells
4 characteristics of carbohydrates
- present as glycoproteins in envelope
- virus-coded
- attach virus to host cell via receptors
- also function as antigens
3 WAYS to cultivate viruses
- Embryonated Eggs
- Living Animals
- Cell Cultures
a scientific process that involves cultivating eggs to isolate and identify viruses, and produce vaccines
Embryonated eggs
Main process of EMBRYONATED EGGS(1) and results (3)
Inoculated/Inject with animal virus
VIRAL GROWTH:
- death of embryo
- cell damage of embryo
- formation of lesions
2 processes in cultivating viruses in living animals
- animal is observed for signs of disease
- killed so infected tissues can be examined for the virus
3 phases in cultivating viruses in cell cultures
- Tissue in test tube is treated w enzymes to separate the cells
- Cells are suspended in culture medium
- Normal cells - replicate in a monolayer
Transformed cells - replicate in multiple layers (can grow indefinitely like cancer cells)
3 ways to detect virus infected cells
- Cytopathic effects
- Hemagglutination test
- Plaque Assay
DIFF in # of nucleus in Cytophatic effects:
HEALTHY CELL VS INFECTED CELL
Healthy: one nucleus / cell
Infected: numerous nuclei / cell
3 possible reactions in the Hemagglutination test
- Healthy RBC = no reaction
- Infected RBC = Hemagglutination
- Infected RBC w/ injected antibody = Hemagglutination inhibition
hemagglutinin
- type of protein
- location
- main function
- glycoprotein
- surface of influenza viruses
- helps the virus bind to and infect a host cell
In Plaque Assay for Detection of Infected Cells, what do the agar plates look like?
On agar plate, bacterial (host) culture is mixed with bacteriophages
After incubation, darker spots indicate successful infection of bacterial cells
5 basis of classification of viruses
- genome
- structure
- route of transmission
- immunological properties
- pathology/symptomatology
4 possible routes of transmission of viruses
- enteric
- respiratory
- zoonotic
- sexually-transmitted
5 stages of Viral Replication Processes
- Attachment and Penetration
- Synthesis of viral nucleic acid and protein
- Assembly and packaging of new virus
- Cell lysis and release of new virions
Can viruses diffuse across biological membranes to infect a host cell? (like water molecules lang?)
No, they infect host cells with MEMBRANE PROTEINS that facilitate their attachment
after successful attachment, they enter through endocytosis
What is PHAGE VIRION ADSORPTION?
other term for the bacteriophage attaching itself to he host cell
3 ways of entry of ANIMAL VIRUSES
- Direct penetration
- Membrane fusion
- Endocytosis
TYPES OF ENTRY OF ANIMAL VIRUSES
Direct Penetration
- Naked virus attaches to receptors on cell membrane of host cell
- Only the viral gene enters the host cell
TYPES OF ENTRY OF ANIMAL VIRUSES
Membrane Fusion
- The glycoproteins on the envelope of the virion attaches to the cell membrane receptors of the host cell
- As the virion enters the host cell, its envelope fuses with the cell membrane of the host cell
- Thereby allowing ONLY the capsid w/ the viral genome to enter
TYPES OF ENTRY OF ANIMAL VIRUSES
Endocytosis
- The glycoproteins on the envelope of the virion attaches to the cell membrane receptors of the host cell
- As the virion enters the host cell, the cell membrane of the host cell surrounds the entire virion (w/ envelope so double enveloped na sya)
- The cell membrane host envelope and the viral envelope breaks down intracellularly and releases the viral genome
2 ways for viruses to be released from the host cell
- Budding
- Host Cell Lysis/Death
Process of release of enveloped viruses (BUDDING)
- Viral spike proteins and Viral matric proteins are inserted on the outside and inside of the Host cell membrane respectively
- Virus is enclosed by the stated region
- Virus is released by budding
DNA vs RNA replication process
DNA/RNA
1. attachment and penetration
RNA
2. Protein synthesis
3. NA synthesis
4. Protein synthesis
5. Assembly
6. Release
*DNA didiretso sa #3 from #1
3 examples of bacteriophages
- Listeria bacteriophage
- T4 phage
- P1 bacteriophage
2 main types of bacteriophages
- Lytic/Virulent
- Temperate/Lysogenic
TYPES OF BACTERIOPHAGES
kills host after infection (cell lysis)
Lytic
TYPES OF BACTERIOPHAGES
produces large # of virions
Lytic
TYPES OF BACTERIOPHAGES
replicates with the host genome
Temperate
TYPES OF BACTERIOPHAGES
viral DNA is transmitted genetically from one host to daughter cells w/o dying
Temperate
What cycle can still occur in temperate bacteriophages even though host cell will not lysis?
Lytic cycle or Lysogenic Cycle
LYTIC CYCLE process
- Protein fiber on the phage tail attach to host cell membrane receptors
- Viral Genome gets injected to the host cell
- Phage DNA -> mRNA -> Phage proteins
- Phage DNA is replicated and #3 is repeated
- Large # of Phage DNA is assembled to form the mature phages
- Mature phage releases enzyme that breaks down cell wall of the host cell which causes it to lysis
What enzyme is released by mature lytic bacteriophages that causes the host cell to lysis?
Phage-induced lysozyme
LYSOGENIC CYCLE process
- Protein fiber on the phage tail attach to host cell membrane receptors
- Viral Genome gets injected to the host cell
- Viral Genome integrates to the host cell genome through RECOMBINATION
- Host cell genome w/ viral genome replicates
- Host cell itself replicates (2 cells with a mixture of host and viral genome)
- The 2 host cells may undergo lytic cycle or lysogenic cycle again
LYSOGENIC PROCESS
What do you call the section of the viral genome that gets integrated to the host genome
Prophage DNA
LYSOGENIC PROCESS
What do you call the entirety of the host cell that houses a mixture of its original genome + section of viral genome
Lysogenic bacterium/cell
If a lysogenic host cell undergoes lytic cycle, what is the preliminary stage?
Prophage is excised from the bacterial (host cell) chromosome
