Exam 4 - Chapter 19

Question 1

types of viruses

Answer 1

noncellular - infectious particles

obligate intracellular paracites - replicate by infection host

Question 2

origin of viruses

Answer 2

• regressive hypothesis- viruses evolved from free living cells or from intracellular prokaryotic parasites
• progressive phypothesis-viruses originated from RNA, DNA, or some other self replicating molecule
• virus first hypothesis- viruses are teh first self replicating entities

Question 3

retrovirus

Answer 3

viruses that insert their genome into the host cells

Question 4

reverse transcriptase

Answer 4

converts RNA into DNA before its inserted into the host cell

Question 5

Viral genome may contain

Answer 5

• double or single stranded DNA
• double or single stranded RNA
• Can be linear or circular
• Depending on nucleic acid determines DNA or RNA virus

Question 6

Viral Capsids

Answer 6

• helical
• isochedral
• enveloped
• head-and-tail

Question 7

host range

Answer 7

limited number of host species that it can infect

Question 8

Replication cycle of animal viruses

Answer 8

• Adsorption: virus attaches to receptor sites on host cells membrane, requires exact fit
• Penetration: membrane of host is penetrated by entire virus, capsid/nucleic acid, or just nucleic acid; 3 methods – endocytosis, fusion, shape change
• Uncoating: enzymes dissolve viral envelope and/or capsid if present
• Synthesis/Assembly: viral nucleic acids control host cells metabolic machinery, mature virus particles are constructed spontaneously
• Release: enveloped viruses are released by budding, naked viruses released through lysis or apoptosis

Question 9

effects of animal virus

Answer 9

-Symptoms of viral infections result both from cell damage from viral taking a piece of the host cells plasma replication and from the immune response
-Acute infection – symptoms appear for a short time and the virus is eliminated
-Chronic infection – long lasting and may not result in viral elimination and recovery
-Intermittent or latent infections – virus can remain dormant and reinfection can occur over months or many years
• Asymptomatic infections – no symptoms
• Some infections are associated with cancer

Question 10

bacteriophage

Answer 10

viruses that infect bacteria

Question 11

phage replication

Answer 11

through lytic and lysogenic cycle

Question 12

lytic cycle

Answer 12

• adsorption, penetration, synthesis & assembly, and release
• Release occurs through lysis which kills the host cell releasing many new phage at the same time

Question 13

lysogenic cycle

Answer 13

• adsorption, penetration
• doesn’t directly kill host
• prophage incorporated into host cells genome, environment can trigger lytic cycle later

Question 14

temperate phage

Answer 14

phage that undergoes the lysogenic cycle

Question 15

Prion proteins (PrP)

Answer 15

occur naturally in the vertebrate nervous system but can cause fatal disease when they misfold

Question 16

PrPc

Answer 16

• glycoprotein normally found on the surface of certain cells
• secondary structure dominated by alpha helices

Question 17

PrPsc

Answer 17

• same amino acid sequence as the normal protein

- secondary structure dominated by beta conformation

Question 18

Prion examples

Answer 18

scrapie, mad cow, chronic wasting disease, creutzfeld-jakob disease