Viruses

Question 1

Viruses are obligate parasites because…

Answer 1

…they require a host cell to replicate

Question 2

Virus Features (3)

Answer 2

• Infectious non-cellular agents
• No nucleus, organelles, or cytoplasm (occasional enzymes)
• Contain either DNA or RNA (single or double stranded), but never both

Question 3

Virus Structure

Answer 3

• Nucleic acids of some sort in linear structure (sometimes circular)
• Capsid: protein coat consisting of capsomeres that give distinctive shapes
• Some have outer shell called an envelope made of a lipid bilayer

Question 4

Virus Size

Answer 4

-Genome range from 2e3 bp to 2.4e6 bp

Question 5

A virus outside of a host is called…

Answer 5

…a virion

Question 6

The capsid and nucleic acids together are called…

Answer 6

…the nucleocapsid

Question 7

Envelopes are used for…

Answer 7

…attachment of the virus to host cell; sometimes contain spikes for attachment

Question 8

A virus without an envelope is considered a…

Answer 8

…naked virus

Question 9

Most viruses are… (size)

Answer 9

…0.02-0.3 um

Question 10

Bacteriophage Lytic Cycle (3)

Answer 10

1. Biosynthesis: Production of phage DNA and proteins
2. Maturation: Assembly of phage particles
3. Release: Phage lysozyme breaks cell wall

Question 11

Bacteriophage Lysogenic Cycle (2)

Answer 11

1. Integration: phage DNA will integrate into bacterial chromosome to become a prophage
2. Exit: Under certain conditions, prophage will excise itself and go into lytic cycle

Question 12

Bacteriophage Terminology (2)

Answer 12

• Attachment: Phage attaches by tail fibers to host cell

- Penetration: Phage lysozyme opens cell wall; tail sheath contracts to force tail core and DNA into cell

Question 13

Animal Virus Multiplication (6)

Answer 13

• Attachement: Viruses attach to cell membrane
• Penetration by endocytosis (pinocytosis) or fusion (envelope fuses with membrane)
• Uncoating by viral or host enzymes
• Biosynthesis: Production of nucleic acids and proteins
• Maturation: Nucleic acid and capsid proteins assemble
• Release by budding (enveloped viruses) or rupture

Question 14

Viral Species

Answer 14

A group of viruses sharing the same genetic information and ecological niche

Question 15

HIV Structure

Answer 15

• Surface glycoproteins (gp120) needed for attachment to host cell CD4 receptors
• Viral nucleocapsid that enters cell with enzymes, RT, proteases, and integrase

Question 16

CD4 receptors are found on…

Answer 16

…macrophages and CD4+ T-cells

Question 17

HIV Enzymes (4)

Answer 17

1. RT - RNA to DNA (high mutation rate)
2. Integrase - Integrates viral DNA into host DNA
3. RNA Polymerase - Transcribes viral DNA into viral RNA
4. Protease - Slices proteins into cores that interact with viral mRNA to form new viruses, which bud off and infect more cells

Question 18

HIV Infection

Answer 18

1. gp120 binds to CD4 receptors and CXCR4 in T-cells or CCR5 in macrophages
2. Virus membrane fuse with host cell
3. Nucleocapsid enters and releases viral RNA and enzymes
4. RT converts viral RNA to DNA
5. Integrase integrates viral DNA into host DNA
6. New viral RNA is used as genome and to make new viral proteins
7. Proteins and RNA move to cell surface and bud off it
8. Protease cleaves and processes viral proteins for maturation

Question 19

Epidemiology of HIV

Answer 19

• 33 million infected

- Prevalent in USA, Russia, and Southern Africa

Question 20

ART

Answer 20

• Antiretroviral Therapy

- Uses cocktail of antiretrovials (ARVs)

Question 21

Classes of ARVs (4)

Answer 21

1. Fusion inhibitors
2. Nucleoside RT inhibitors (NRTIs)
3. Non-nucleoside RT inhibitors (NNRTIs)
4. Protease inhibitors (PI)

Question 22

HIV is difficult to treat because…

Answer 22

…it can “hide” from immune system in host DNA; ARVs kill free floating virus only, suppressing but not eliminating it

Question 23

Early ART can…

Answer 23

…prevent transmission and treat HIV

Question 24

This mutant can confer immunity to HIV

Answer 24

CCR5