Module 2: Section 1A

Question 1

2 main virus structures

Answer 1

1. Nonenveloped viruses
2. Enveloped viruses

Question 2

Nonenveloped viruses

Answer 2

• Simplest virion
• Consists of a capsid made of protein and nucleic acid (either DNA or RNA)

Question 3

Enveloped viruses

Answer 3

• Surrounded by a lipid membrane that has embedded viral proteins
• When these proteins project from the surface, there called spikes

Question 4

Bacteriophages

Answer 4

• Virus that infects bacteria
• Usually nonenveloped
• Many have a “tail” that helps bind to the target host cell and inject viral DNA into it

Question 5

5 steps of lytic cycle of a bacteriophage

Answer 5

1. Infection
2. Replication of viral genetic information
3. Production of viral proteins
4. Assembly of viruses
5. Lysis of bacterium

Question 6

1. Infection - lytic cycle

Answer 6

Phage attaches to surface of bacterial cell and injects its viral genetic information into the cell

Question 7

2. Replication of viral genetic information - lytic cycle

Answer 7

Viral genetic information replicates using host cell machinery

Question 8

3. Production of viral proteins - lytic cycle

Answer 8

Host machinery makes the component parts of new phage

Question 9

4. Assembly of viruses - lytic cycle

Answer 9

Using the component parts, new phages are created

Question 10

5. Lysis of the bacterium - lytic cycle

Answer 10

• Bacterium cell wall degrades and new phages are released
• Accomplished by phage protein “lysin”

Question 11

Lysogenic cycle

Answer 11

• Phage DNA is incorporated into the host genome
• Is passed on to subsequent generations of the host cell
• Until it is induced to enter lytic cycle

Question 12

How non enveloped viruses infect eukaryotic cells

Answer 12

• Enter host by binding to a receptor on cell surface
• Taken into cell by endocytosis
• Capsid is degraded, releasing the viral genome
• Viral genome is transported to the nucleus for replication

Question 13

The proteinaceous

Answer 13

• Outer structure of non enveloped viruses
• Makes them more tolerant to harsh environmental conditions and disinfectants

Question 14

6 steps of non enveloped viral infection cycle

Answer 14

1. Adsorption
2. Endocytosis
3. Capsid deconstruction
4. Genome replication
5. Assembly
6. Release

Question 15

1. Adsorption - non enveloped viral infection

Answer 15

Virus binds to a host receptor at the cell surface

Question 16

2. Endocytosis - non enveloped viral infection

Answer 16

Virus is taken into the cell via endocytosis

Question 17

3. Capsid deconstruction - non enveloped viral infection

Answer 17

Viral genome is released into cytoplasm after degradation of the viral capsid

Question 18

4. Genome replication - non enveloped viral infection

Answer 18

Viral genome is replicated inside host cell nucleus and transcribed to direct viral protein synthesis

Question 19

5. Assembly - non enveloped viral infection

Answer 19

Viral proteins are synthesized, modified, and assembled with the viral genome to form new viral particles

Question 20

6. Release - non enveloped viral infection

Answer 20

Progeny viruses are released from cell upon lysis of host cell

Question 21

5 steps of enveloped viral infection cycle

Answer 21

1. Attachment
2. Uncoating
3. Genome replication
4. Proteolytic processing by viral protease
5. Budding

Question 22

1. Attachment - enveloped viral infection

Answer 22

Initial virus attachment is mediated by viral “spike proteins” gp41/gp120 that interact with host protein CD4

Question 23

2. Uncoating - enveloped viral infection

Answer 23

Virus fuses with host-cell membrane, releasing the genome from the capsid

Question 24

3. Genome replication - enveloped viral infection

Answer 24

• Viral genome is reverse transcribed into DNA and integrated into cellular genome
• It undergoes genome replication and is transcribed into mRNA

Question 25

4. Proteolytic processing by viral protease - enveloped viral infection

Answer 25

- The precursor polypeptide is cleaved via proteolysis to produce viral components - They are now ready for assembly at the cell membrane

Question 26

5. Budding - enveloped viral infection

Answer 26

- Viral proteins assemble at the cell membrane, producing a new viral particle - Particle then buds to release enveloped virion - Lipid components of envelope are derived from host cell membrane