Viruses

Question 1

Lysogenic Phase

Answer 1

• Dormant Phase
• May or may not destroy the cell
• Extracellular penetration uncoating
• Viral genome attaches to Host cell DNA

Question 2

Lytic Phase (bacteriophage)

Answer 2

• Destroys the cell
• 99.9% of virus
• Intracellular penetration uncoating
• Nucleic acid kills the Host cell DNA

Question 3

Lysosome:

Answer 3

The enzyme that helps the bacteriophage get into the cell.

Also, helps the bacteriophage get out of the cell because after replicating itself, there are a lot of more bacteriophages that carry a lot of more lysosome enzymes.

Question 4

Lytic Phase (bacteriophage) : replication/biosynthesis

Answer 4

• Destroying the Host cell’s DNA
• Replicating itself
• The Host cells transcription and translation machinery is turned off

Question 5

Lysogenic phase: replication/biosynthesis 3A

Answer 5

• Virus DNA integrates into Host cell DNA
• Host cells transcription and translation is turned on (Host DNA + Virus DNA is getting reproduced)

Question 6

Lysogenic Phase: Biosynthesis -> Lytic Cycle

Answer 6

• Virus becomes induced by a stressor and exists the host cell’s genome
• Now, the host cell’s transcription and translation are turned off

Question 7

Retrovirus

Answer 7

RNA -> DNA -> RNA -> Proteins

• Enzyme: Reverse Transcriptase
• HIV (dormant until stress induced)

Question 8

Virus characteristics:

Answer 8

• Small (need to fit into the cell)
• Obligate parasites (can’t complete its job without a host)
• Host cell specific (specific receptors for attachment)
• No cellular organelles (nothing to target making antimicrobial difficult)
• Contain a protein coat called a capsid (shape and protection)
• Contain DNA or RNA
• Can’t metabolize (because they require a host cell)
• Dormant (non-living)

Question 9

Naked Virus

Answer 9

• Contain a genome (RNA or DNA)
• Have a capsid (protein)
• Not fully assembled because they don’t have a lipid bilayer envelope (they are not infectious)
• Destroys the whole cell

Question 10

Enveloped Virus

Answer 10

• Contain a genome (RNA or DNA)
• Have a capsid (protein)
• Surrounded by a biological membrane (envelope: lipid bilayer that contains lipids and proteins)
• The envelope acts as a shield and makes it difficult for the host immune to attack
• May or may not destroy the whole cell

Question 11

Specialized Transduction

Answer 11

Specific genes are transferred between bacteria by a phage at the end of the lysogenic cycle and the bacteriophage enters the lytic cycle

Question 12

Generalized Transduction

Answer 12

Random genes are transferred between the bacteria by a phage during the lytic cycle

Question 13

Lytic Cycle (eukaryotic cells)

Answer 13

Enters through endocytosis (naked virus) OR membrane fusion (enveloped virus)

• Lysosome in the human cell break the capsid of the. naked virus (intracellular uncoating)
• The lipid bilayer of the envelop virus makes a structural change to the the cell membrane it took with it into the virus (membrane fusion) Allowing the virus genome to enter the cell.
• Biosynthesis: transcription and translation is turned off. The virus can now replicate itself.
• Destroys the whole cell

Question 14

Latency Cycle (eukaryotic cells)

Answer 14

• Virus remains dormant within the host cell
• The viral genome is present but is not actively replicating
• The virus can reactivate due to a stress inducer
• A lifelong infection and a reoccurring disease

Question 15

Latent human viruses have been linked to cancer:

Answer 15

• Epstein-Barr: T/B cell lymphoma
• HPV: Cervical cancer
• Hepatitis C: liver cancer

Question 16

“Two Hit Theory”: Oncogenes

Question 17

“Two Hit Theory”: Oncogenes & Inactivated Tumor Suppressor Genes

Answer 17

• Proto-oncogenes: a normal gene cell that stimulates cell division/growth
• Oncogenes: a mutated gene from a proto-oncogene. This gene promotes cancer. Now, a rapid production of the modified protein.
• Tumor Suppressor Genes: slow down cell division, repair DNA mistakes, or communicate apoptosis.

Inactivated Tumor Suppressor Gene: if this gene is turned off by a mutation, it has a loss-of-function –> cause cancer

Question 18

How do we study viruses: Tissue Culture

Answer 18

• Tissue Culture: since viruses are obligate parasites (they need living cells to replicate), tissue culture provides the living cells so researchers can grow and study viruses in a lab.

Question 19

How do we study viruses: Embryonated Eggs

Answer 19

• Embryonated Eggs: fertilized eggs that are used to create a suitable environment for viral replication.

Question 20

How do we study viruses: Plaque Assays

Answer 20

• Plaque Assays: the process of diluting a sample to obtain a range of concentrations. You can observe damage of cells caused by the viral infection in a clear zone of replication virus particles.

Question 21

Antivirals: 1) Attachment

Answer 21

Ex. Maraviroc - covers the receptor for the HIV virus which blocks viral penetration of HIV

Question 22

Antivirals: 2) Intracellular Uncoating

Answer 22

Ex. Amantadine - preventing the virus from releasing its genetic material within the host cell

Question 23

Antivirals: 3) Inhibition of Nucleic Acid

Answer 23

Ex. Acyclovir & AZT -

• Acyclovir - mimics guanosine nucleotides
• AZT - inhibits reverse transcriptase

Question 24

Antivirals: 4) Inhibition of Assembly/Maturation

Answer 24

Ex. Protease inhibitors - target viral proteases (polypetides into functional proteins), preventing the assembly and halting replication

Question 25

Prions

Answer 25

- Infectious proteins that cause dementia in humans and animals - Discovered by Dr. Stanley Prusiner - Sheeps: Scrapie (through contact with the placenta and birth fluids of infected ewes during lambing) - Cows: Mad Cow Disease (through the consumption of contaminated feed containing prions) - Humans: Kuru (consumption of brain tissue from deceased individuals that have prions), Creutzfeldt-Jacob Disease (sporadic/unknown, genetic inheritance, consumption of contaminated meat)