04 Virology Duncan

Question 1

What are two essential components for Viruses?

Answer 1

A little bit of nucleic acid (the plans). A few proteins

Question 2

What are the two essential features of Viruses?

Answer 2

Replication machinery. Travel machinery

Question 3

What do ancestral transposons have the ability to do?

Answer 3

“Hop out” and “Hop in” to DNA, making copies of itself in the process. It lives a “nuclear” existence

Question 4

What is some general information on Transposons?

Answer 4

Pick up neighbor genes during the “hop-in/hop-out” process; sometimes these will allow it to: obtain a protein coat, providing cytoplasmic stability. Obtain specific coat proteins that allow receptor binding and internalization (i.e. infection). Acquisition of additional proteins can provide active exit from cells, and facilitate re-entry (otherwise, release would require cell lysis)

Question 5

What are genes like in viruses?

Answer 5

3-5 genes in smallest, to > 100. Viral genes frequently resemble human genes

Question 6

What is the Flu virus life cycle like?

Answer 6

Binds to receptor; pit (endosome) forms. Delivers RNA to cytoplasm. RNA is released, translocated to the nucleus. Many copies are made for inclusion in new particles. Viral RNA also serves as template for protein synthesis. Viral RNAs and viral proteins associate, move to the cell membrane, and are released as new infectious particle with human membrane. Release requires activity of viral neuraminidase protein

Question 7

What is the life cycle of Hepatitis C like?

Answer 7

Binds to receptor; pit forms; delivers RNA to cytoplasm. Ribosome makes polymerase from viral mRNA, which is released into cytoplasm. Polymerase makes antisense copies of viral RNA. As RNA serves as template to make many more viral RNAs. Viral RNAs and viral proteins associates, pass through golgi, and are released as new infectious particle with human membrane

Question 8

What is the life cycle of HIV like?

Answer 8

Binds to receptor. Membranes fuse, releasing RNA to cytoplasm. Viral RNA reverse transcription by virion-associated RT. Which translocates to nucleus and integrates into DNA (requires HIV enzyme integrase). Integrated DNA is a template to make mRNA which makes proteins, and to make RNA for inclusion in progeny infectious particles. Viral RNAs and viral proteins associate and are released as new infectious particle with human membrane

Question 9

What is a principle difference between HIV, Hep C, and the Flu’s life style?

Answer 9

A principle difference is where the nucleic acid is replicated (cytoplasmic or nuclear). A second important difference between RNA viruses is the form and use of the genomic RNA (positive or negative strand; only for SS-RNA)

Question 10

What is an example of a DNA virus?

Answer 10

HPV

Question 11

What are some examples of RNA viruses?

Answer 11

Poliovirus, HCV. Influenza. HIV

Question 12

What is Budding Infection?

Answer 12

The particle forms within the cell, migrates to the interior cell surface, where it evaginates while absorbing a coating of plasma membrane

Question 13

What is Lytic Infection?

Answer 13

A large number of mature viral particles form within the cytoplasm; a total disruption of the plasma membrane is induced, resulting in viral particle release and cell death

Question 14

What is Viral Tropism?

Answer 14

Determined by viral cell surface protein/human receptor protein interaction. Some receptors are tissue specific; others occur on many cell types. Viral surface protein mutations can alter tropism

Question 15

What do Rhinovirus often use to attach?

Answer 15

Infect cells via attachment to ICAM-1

Question 16

What does HIV require to attach to macrophages?

Answer 16

GP120 attaching to CD4 and CCR5

Question 17

What mutation allows HIV to attach to both T-Cells and Macrophages (Dual-Tropic HIV)?

Answer 17

Altered GP120

Question 18

What is Pseudotyping?

Answer 18

Altering or mutating viral cell surface proteins, either naturally or by human intervention, which changes viral tropism

Question 19

What are some common viruses that can cause cancer after infecting humans?

Answer 19

Hep B, Hep C; Papilloma viruses; EBV

Question 20

What do the viruses that cause cancer have?

Answer 20

These viruses contain human genome-related sequences encoding cancer-causing proteins (transforming genes (ras, fos, Abl), related to and acquired from human genes)

Question 21

What is the principle defense against viral infections?

Answer 21

Vaccination. Vaccines provide exposure to antigens (active immunity). An interval is required for immunity to develop. Passive immunity: injection of serum antibodies (won’t be as long term)

Question 22

What is the difficulty in finding drugs for viruses?

Answer 22

Small genomes mean very few targets. Similar proteins. Frequency of mutations to resistance

Question 23

What are the innate defense systems against viruses?

Answer 23

Interferon response. Immune response

Question 24

What occurs in the Interferon Response?

Answer 24

Primary virus infects a producing cell. The virus also releases Pathogen-Associated Molecular Pattern (PAMP) which is recognized by the Toll-Like Receptor of the producing cell. This producing cell then creates interferon and releases it to nearby cells. Interferon binds to its receptor which causes the responding cell to create a transcription factor that makes antiviral proteins (ADAR, PKR, 2,5AS). When a secondary virus then tries to infect this cell, it won’t be able to