Viruses and prions

Question 1

What aren’t viruses?

Answer 1

not living; they are acellular

Question 2

What are viruses?

Answer 2

Small infectious particles
Obligatory intracellular parasites
Inert outside cells and hijack cell replication machinery

Question 3

What do all viruses carry?

Answer 3

Genome (DNA or RNA)
Capsid (protein coat)

Question 4

What are DNA and RNA viruses?

Answer 4

Double stranded and single stranded

Question 5

What can viral protein coats contain?

Answer 5

Viral glycoproteins for cell entry

Question 6

What are the building blocks of capsids?

Answer 6

Capsomeres

Question 7

What surrounds some capsids?

Answer 7

Envelope

Question 8

What is sent to the plasma membrane before a virus buds?

Answer 8

Viral glycoprotein

Question 9

What happens when a virus has no envelope?

Answer 9

Glycoproteins are attached to the capsid

Question 10

What is the new plasma membrane of a virus composed of?

Answer 10

Phospholipid bilayer

Question 11

What is the envelope of a virus a combo of?

Answer 11

Glycoproteins and host cell molecules

Question 12

What is a wide host range?

Answer 12

Multiple species are susceptible

Question 13

What is a narrow host range?

Answer 13

Single species/cell in species are affected

Question 14

What is the host range dictated by?

Answer 14

Lock and key recognition

Question 15

What does the lock and key recognition mean?

Answer 15

Viral glycoproteins are keys that bind specific host cell surface receptors (locks)

Question 16

What are the steps of viral replication?

Answer 16

Attachment
Entry
Synthesis
Assembly
Release

Question 17

What does a virus focus on getting inside of a host cell?

Answer 17

Its viral genome

Question 18

What is lytic replication?

Answer 18

Bacterial chromosome is destroyed to take away the competition

Same replication cycle

Question 19

What is cell lysis?

Answer 19

In lytic replication- New phage is released- no envelope

Question 20

What is the cycle of bacteriophages?

Answer 20

Attachment
Entry
Provirus
Replication of chromosome and virus- (cell division)
Further cell division
Induction
Synthesis
Assembly
Release

Question 21

What is pro virus?

Answer 21

Step in lysogenic replication cycle in bacteriophage

Means that bacteriophage DNA is integrated into bacteria chromosome

Happens in animal viruses

Question 22

What are the mechanisms of virus entry?

Answer 22

Direct penetration
Endocytosis
Membrane fusion

Question 23

What are principles of direct penetration?

Answer 23

Can’t have an envelope
Capsid stays outside cell (what bacteriophage do)
Genome is injected into cell

Question 24

What is endocytosis?

Answer 24

Membrane of host reaches around and engulfs the virus

Virus is brought into an endosome

The virus is released from the endosome into the host cell cytoplasm

Can be enveloped or non-enveloped viruses

Question 25

What is membrane fusion?

Answer 25

Can only happen with enveloped viruses Membrane is brought to the viral envelope and fuses The viral glycoprotein stays at the surface

Question 26

What happens in a host cell when invaded by a DNA virus?

Answer 26

Viral genome is replicated by cell DNA polymerase in the nucleus Host RNA polymerase transcribes DNA to RNA in the nucleus Ribosome translates RNA into proteins in the cytoplasm

Question 27

What happens in a host cell when invaded by an RNA virus?

Answer 27

Virus needs special viral enzyme because genome does not match host cell’s Viral genome is replicated by RNA polymerase in the cytoplasm Ribosomes translate RNA into proteins in the cytoplasm New viral genomes and proteins assemble in eukaryotes

Question 28

Where does DNA viruses assemble in host cells?

Answer 28

Nucleus

Question 29

Where do RNA viruses assemble in the host cell?

Answer 29

Cytoplasm

Question 30

How do non enveloped viruses leave host cells?

Answer 30

By lysis (plasma membrane ruptures)

Question 31

What is another way non-enveloped viruses sometimes leave host cells?

Answer 31

Exocytosis- vesicle with virus inside is transported to cell surface and fusion event allows virus to leave the cell

Question 32

How do enveloped viruses leave host cells?

Answer 32

Budding

Question 33

What are prions? Where are the majority of them?

Answer 33

Misfolded normal cellular proteins Majority in brain

Question 34

What can prions cause?

Answer 34

fatal Spongiform encephalopathies

Question 35

What are the 4 types of spongiform encephalopathies?

Answer 35

Scrapie (sheep), mad cow disease, kuru (New Guinea cannibals), Creutzfeldt-Jakob disease (spontaneous in humans)

Question 36

How are prions destroyed?

Answer 36

Incineration/autoclaving in concentrated sodium hydroxide

Question 37

How are prions transmitted?

Answer 37

Ingested Transplantation Contact mucous membranes with infected nervous tissue

Question 38

What is the incubation period for prions? When does illness occur?

Answer 38

5 to 40 years 12 to 14 months before death

Question 39

How do prion diseases take over?

Answer 39

Infects brain cell & converts a normal protein into misfolded form

Question 40

What happens when prions build up?

Answer 40

Neuronal death occurs Large vacuoles and plaques form; leads to death of the individual

Question 41

How many types of capsids are there?

Answer 41

4

Question 42

What do capsids do?

Answer 42

Protect genomes

Question 43

Where do DNA viruses assemble?

Answer 43

The nucleus

Question 44

Where do RNA viruses assemble?

Answer 44

Cytoplasm

Question 45

What is released when a virus is assembled?

Answer 45

Capsomeres and genome

Question 46

What is the cycle involved in silent replication called?

Answer 46

Lysogenic cycle

Question 47

What are the 2 methods non-enveloped viruses use to leave a cell?

Answer 47

Exocytosis and lysis

Question 48

How do non-enveloped viruses enter a cell?

Answer 48

Direct penetration and endocytosis

Question 49

What are the 2 methods enveloped viruses use to get inside of a cell?

Answer 49

Endocytosis and membrane fusion

Question 50

What step is unique to lytic replication of bacteriophage?

Answer 50

Bacterial chromosome is destroyed