why is it important to study viruses?
- Participate in HGT: helps lead to evolution and diversity
-Evidence of ancient viral genomes in our DNA
-Human, animal, and agricultural health
-Influence history
What are the main characteristics that dictate that viruses are not living beings?
-Genetic material contained within a protective protein coat
-Subcellular (simpler than a cell)
-OBLIGATE INTRACELLULAR PARASITES
Incapable of replication and mobility
Describe viral size in comparison to a bacterial cell and a eukaryotic cell.
Smaller than animal and bacterial cells
Smallest : 30 nanometers in diameter
Biggest : 800 nanometers
- Measured with electron microscope
- Can't be seen in the range of a regular microscope
What are the three types of bacterial shapes and describe them ?
Helical
-spiral shape
Icosahedral
-Circular Has envelope with spikes
Complex
Spaghetti look like
helical
what is this type virus is this ?
Icosahedral
what is this type virus is this ?
complex
what is this type virus is this ?
What is a virion?
A complete virus particle that is the extracellular infectious form
What two components make up the nucleocapsid of a virus?
nucleic acid genome and capsid
What are the two functions of a viral capsid?
...
What is the capsid composed of?
capsomeres
what is a virion
A complete virus particle that is the extracellular infectious form
What are the parts in a non-enveloped virus?
Nucleocapsid
Capsid
-Protection
Enzyme carrier
Spikes
- Infectivity and specificity
what are the parts in Enveloped Viruses?
Nucleocapsid
Matrix period
Envelope
Spikes
How are viruses classified?
Host organism
Organ / organ system involved
Biology of the virus
- Nucleic acid content
- Capsid structure
- Number of capsomeres
- Other chemical /physical properties
What is are the steps to the viral replication?
1. Absorption(attachment )
2. Penetration
3. Replication
4. Assembly
5. Release
what is occurs in the absorption stage?
Viruses attaches to cell surface receptor molecule by spikes or fibrils, capsids, or envelope
what is occurs in the penetration stage?
Entire viral particle or only nucleic acid genome enters via endocytosis or buy fusion with cellular plasma membrane
what is occurs in the replication stage?
Process is complex, and details depend on the particular virus and its genome structure. Replication of the viral genome may occur in the nucleus or cytoplasm.Once replicated, genes are express leading to production of viral components
what is occurs in the assembly stage?
Components are assembled
what is occurs in the release stage?
Viruses are extruded from host cell by budding (e.g HIV) or lysis of host cell plasma membrane
Why happens with lytic bacteriophage?
1. Phage DNA circularizes and enters lytic or lysogenic cycle
Lytic
2. Genome is infected in bacterium
3. New phage DNA and proteins are synthesized and assembled into virions. Accumulates till the bacteriophage can't hold the virions anymore.
4. Cell lys
what occurs when a lysogenic bacteriophage ?
1. Phage DNA integrates within the chromosomes by recombination becoming a prophage
2. Lysogenic bacterium multiplies normally and many cell divisions pform
3. Occasionally, the prophage may excise from the chromosome by another recombination event, initi
what is the difference between lysogenic & lytic?
lysogenic: integrated lytic: enters
Consequences of lysogeny
Change in the phenotype of bacteria that are infected with a phage due to integration in the bacterial chromosome
Ex. streptococcus pyogenes
What is the step of the eukaryotic replication?
1. Adsorption
2. Penetration
3. Replication
what occurs is adsorption ?
a. Virus attaches to cell via specific cell surface receptors
b. Recognition specificity establishes host range
c. Not uncommon for eukaryotic virus
what occurs is
Penetration ?
A. Delivery of viral genome into host cell cytoplasm (3 types)
- Only the nucleic acid enter the cell and the virion remains outside the cell (e.g. phage, polio)
- Some envelope fuses with the host cell membrane to release nucleocapsid
- Other enveloped v
what occurs is
replication?
A. Replication process is dependent upon the genome type of the virus (DNA or RNA, ss or ds)
B. Genome contains the blueprints for making the parts of the virus
C. Various viral parts (protein and nucleic acid) are manufactured using machinery and buildin
what special enzyme does - sense RNA
Negative Sense RNA Viruses carry special enzymes called rna dependent rna polymerase
Are retroviruses positive or negative?
positive
why are retroviruses special?
They are able to integrate their viral genome into our host cell eukaryotic DNA. They can do this with reverse transcriptase
reverse transcriptase
Carried in the virion
turns DNA into rna
Eukaryotic Viral Replication Steps
1. DNA->Transcription ->Translation -> Structural Proteins enzymes
what is the + Sense RNA viruses replication process ?
when a positive sense RNA enters a cell it immediately begins translating and makes viral proteins and viral genomes by hijacking the whole cell ribosome taking over the eukaryotic host cells translation process
+ RNA -> translation -> structural proteins
what is the - sense RNA viruses replication process ?
Cannot begin translation immediately. The negative sense strand of RNA has to be transcribed first in order to make mRNA cant be read immediately by the host cells ribosomes into viral proteins
-RNA -> transcription with virus rna dependent RNA polymerase
What is the assembly process?
Once all the vitral parts (viral genome & viral proteins) are made by the host cell-> self assemble to make new virions
what is the process of release?
Enveloped virions -> released by budding, acquires envelope by exiting through Golgi apparatus, nuclear membrane, or cytoplasmic membrane of host cell
Lipid envelope is a lipid bilayer which looks similar to a host cell membrane
what are naked virions?
rupture (lyse) host cell or released by exocytosis
what are enveloped virions ?
a. Naked virions-> rupture (lyse) host cell or released by exocytosis
b. Enveloped virions -> released by budding, acquires envelope by exiting through Golgi apparatus, nuclear membrane, or cytoplasmic membrane of host cell
Lipid envelope is a lipid bilay
what are the outcomes from viral infections?
1. Death
2. Transformation
3. Latent infection
4. Chronic slow infection
describe the death outcome form a viral infection
Host cell function shuts down as a result of the cell being used for viral replication
Host cell dies
describe the transformation outcome form a viral infection
Infection activates or introduces genes that result in uncontrolled cell growth (including cancer)
describe the latent infection outcome form a viral infection
Virus survives in a "sleeping" state
Does not produce signs of a clinical infection until viral reactivation
describe the chronic slow infection outcome form a viral infection
Cause disease after many years of slowly developing
what are the rules to cultivation (growth of viruses)?
Must be grown in living cells
- Bacteria used for phage growth
- Animal viruses can be grown in animals
-Alternative to use of live animals
-Embryonated chicken eggs
Cell culture
what are cell cultures grown in ?
stock culture and grown in the flask