Viruses Flashcards
What is a virus?
A virus is an infectious particle of genes packed in a protein coat
What are the 3 structures in a virus?
1) Genome
2) Capsid: Protein shell of the virus
3) Envelope: membrane derived from the host cell that surrounds animal viruses
4 Parts of the Virus Genome Structure
i. DNA or RNA
ii. Single stranded or double stranded
iii. Linear or circular
iv. Single Piece of Multiple Pieces
4 Parts of the Virus Capsid
i. Capsomere: protein subunit at capsid
ii. Rod-shaped: helical virus
iii. Polyhedral: icosahedral virus
iv. Complex: icosahedral head and helical tail
Viral Replicative Cycles
Obligate Intracellular Parasite: can only replicate inside the host cell. The virus lacks enzymes for making macromolecules
Host Range: limited number of species a virus can infect
i. lock and key fit or viral surface proteins
and host receptor
ii. Ex: West Nile Virus: affects horses,
moquitos, birds, humans
iii. Ex: Measles: affects humans only
What is the name of a Bacterial Virus?
A Phage
What is the Lytic Cycle of a Bacterial Virus?
It is the replicative cycle that ends in the death of the host cell.
What is the Virulent in a Bacterial Virus?
The Virulent is the virus that replicates only by a lytic cycle.
What are the five T4 Phage steps of a Bacterial Virus?
1) Attachment: the T4 phage uses its tail fibers to bind to specific receptors on E.coli.
2) Entry: the T4 phage DNA is injected into the cell. The empty capsid is left outside, viral enzymes are expressed, and hydrolyze the host DNA.
3) Synthesis: viral genome/proteins are produced using the host’s components.
4) Assembly: the virus genomes are packed into capsids
5) Release: viral enzymes break down bacterial cell wall and the fluid enters. The inside of the cell is hypertonic, and the outside is hypotonic. Water goes from hypo to hypertonic, the cell bursts, and 100-200 viral particles escape.
What are two examples of a T4 phage in humans?
Influenza (flu) and adenovirus (cold).
What is the Lysogenic Cycle of a Bacterial Virus?
It is a replicative cycle that incorporates into the host genome. It doesn’t immediately destroy the host cell.
What is the temperate of a Bacterial Virus?
A virus that uses the lysogenic replicative cycle.
What are the 4 steps in the Lambda phage of a Bacterial Virus?
1) Attachment: same as in the T4 phage.
2) Entry: same as in the T4 phage.
3) Prophage: viral DNA integrates into the host genome.
4) Replication: Normal reproduction of host cell also copies the viral DNA into the new daughter cells
i. Subsequent generations of the host cells
continue to carry the infection
ii. Viral genes can be latent: dormant in
the host (not active/expressed)
iii. Viral genes can be expressed, changing
the host’s phenotype.
a. Ex: Normal gut E.coli turning into
pathogenic food poisoning E.coli.
5) Lytic Cycle: the Lytic Cycle can be
triggered by environmental changes. The virus will replicate and escape when the host cell is threatened
a. Human example: Herpes simplex
virus (cold sores) and hepatitis.
What are the 4 Bacterial Defense Systems?
1) Genetic Diversity: not all cells in a population will have the exact surface receptor proteins to match the virus (aka natural immunity)
2) Restriction Enzymes: bacterial enzymes that recognize and cut the foreign DNA entering the cell. This is a general defense against any virus.
i. Bacterial DNA is methylated (-CH3) to
protect it from its own enzymes.
3) CRISPR-Cas System: long-term, targeted defense against a specific virus.
i. A piece of the viral DNA is incorporated
into the CRISPR region of the bacterial
genome.
ii. Cas nucleuses search out and cut up
any DNA sequence identified in the
CRISPR Region.
4) Evolutionary Arms Race: Bacteria evolve to avoid viral infection, and viruses evolve to beat the bacteria’s defense.
What is the Envelope in an Animal Virus?
The envelope is the membrane that is derived from the host cell and surrounds the animal virus.
