Ch 27: Viruses

Question 0

Virion

Answer 0

• Single virus particle outside of a
  cell
• not alive or dead
• relies on living cells for replication

Question 1

Nature of Viruses

Answer 1

• All viruses have same basic structure
  -Nucleic acid core surrounded by
  Capsid
  -DNA or RNA
  - Circular or Linear
• No cytoplasm: not a cell
  -no ribosomes
• Classified by genome

Question 2

Capsid

Answer 2

Nearly all viruses form protein sheath around nucleic acid core
-composed of 1 to a few proteins

Question 3

Stores Enzymes

Answer 3

Some viruses store specialized emzymes not found in host

Question 4

Shapes

Answer 4

2 simple shapes

- helical: rodlike/threadlike
- Icosahedral: soccer ball shape

Question 5

Complex shapes

Answer 5

T-even bacteria - 2 fold symmetry
-bacteriophage are viruses that
infect bacteria
Pox viruses -multilayered capsids

Question 6

Viral Hosts

Answer 6

Infra cellular parasites in every kind of organism investigated.

Question 7

Host Range (specific invasion)

Answer 7

-Types of organisms infected
-each type of virus has limited
host range
-Tissue tropism: inside a host virus
may only infect a certain tissues
-Viruses can remain dormant for
years
- chicken pox can reemerge as
shingles

Question 8

Replication

Answer 8

Infecting can be thought of set of instructions

• viral genome tricks host into making more viruses
• viruses can only reproduce inside cells.
• can’t synthesize proteins- no ribosomes
• virus hijacks cell’s transcription and translation machineries to express early genes, middle genes, & late genes.
• end result is assembly & release of viruses

Question 9

Viral Genomes

Answer 9

Vary greatly in both type of Nucleic acid and number of strands
- Most RNA viruses are single 
  stranded
     - replicated in host cell's 
       cytoplasm
     - replication in cytosol is error 
       prone
Most DNA viruses double stranded

Question 10

RNA Viruses

Answer 10

• Positive strand virus: viral RNA serves as mRNA
• Neg strand: genome is complementary to viral mRNA
• Retroviruses: employ reverse transcriptase to reverse transcribe viral RNA to DNA

Question 11

Bacteriophage

Answer 11

• Viruses that infect bacteria
• Diverse and united only by bacterial hosts
• Also found in archae
  
  • diff from bacterial viruses

Question 12

HIV

Answer 12

- Causes Acquired Immune  
   Deficiency Syndrome (AIDS)
- 1st reported in 81 but originated 
   from Africa in 50s
- Some people resistant to HIV; 
  others have HIV but don't get AIDS
- Targets CD4+ cells, mainly T cells
- Host usually dies from infection 
  the body would normally fight off.
- Clinical symptoms usually appear 
  after 8-10 year latent period

Question 13

CCR5 Receptor

Answer 13

• Used by HIV May have been used
  by smallpox.
• individuals without receptors are
  resistant

Question 14

HIV Testing

Answer 14

• not a test for circulating virus; test for presence of antibodies against HIV.

Question 15

HIV Infection Cycle

Answer 15

Attachment
   - viral gp120 attaches to CD4     
     protein on macrophages and
     CD4 cells.
Entry
    -through fusion pore
    - Coreceptors like CCR5 affect
      likelihood of entry.
Replication
    -converts RNA to DNA which     
     incorporates into host genome
Assembly
   -makes virus copies
Release
   -new virus exits by budding

Question 16

AIDS Treatments

Answer 16

- FDA lists 35 antiretroviral drugs 
  used in AIDS therapy
- Targets 4 aspects of HIV life cycle
     -viral entry, genome replication,
      Integration of viral DNA, and 
      maturation of HIV proteins
- Vaccine development 
  unsuccessful

Question 17

Influenza

Answer 17

- One of most lethal viruses in    
  human history
- Enveloped animal viruses
     -Type A: serious epidemics in 
       humans & other animals
     - Type B & C: mild human 
        infections
H (hemagglutinin): 
     -aids virus in gaining access to 
      cell interior.
N (neuraminidase):
     -helps daughter viruses break 
      free of host cell once virus 
       replication is done.

Question 18

Origin

Answer 18

New strains of flu tend to come from Far East.
-virus hosts are ducks, cows,
chickens, etc

Question 19

Emerging Viruses

Answer 19

• Viruses that extend their host range
• Often deadly to new host
• Considerable threat in aviation age
• Hantavirus
  
  • causes deadly pneumonia
  • nat. host is deer mouse

Question 20

Ebola

Answer 20

Causes severe hemorrhagic fever
Among most lethal infectious diseases
Host is unknown

Question 21

SARS

Answer 21

• Severe Acute Respiratory Syndrome
• Caused by coronavirus
• Host is civet (weasel-like)
• Mutation rate low compared to HIV
• Vaccine currently being devel.

Question 22

Viruses and Cancer

Answer 22

Viruses may contribute to about 15% of human cancers by altering the growth property of human cells

• triggers expression of oncogenes
• disrupt cell cycle

Question 23

Prions

Answer 23

• Proteinaceous infectious particles
• Proteins that infect brain & cause
  spongy appearance.
  
  • mad cow disease
  • scabies in sheep
  • creutzfeldt: Jacob disease in
    humans (CJD)

Question 24

Viroids

Answer 24

``` Tiny naked mols. of circular RNA Causes disease in plants Autonomously replicate. -info appears to be in 3-D structure ```

Question 25

AIDS

Answer 25

- First recognized in 1980s. - >33 mil people with HIV - Came from SIV Simian immunodeficiency Virus- in 36 primate species

Question 26

Bacteriophage Reprod: | Lytic cycle

Answer 26

``` 1) Attachment or absorption: attaches to part of cell wall 2) Penetration: injection of viral DNA 3) Synthesis: protein & Nucleic acid 4) Assembly: spont. assembly of capsid & enzyme to insert DNA 5) Release: Lysis of cell ```

Question 27

Bacteriophage Reprod: | Lysogenic cycle

Answer 27

- Between penetration & synthesis 1) Integration of genome leads to… 2) Prophage: allows virus replic. w/ host cell's DNA as host cell divides 3) Induction: Prophage exits bacterial chromosome, viral genes are expressed