Topic 5 - Viruses

Question 1

Do viruses predispose humans?

Answer 1

Yes

Question 2

What contribution did Dimitri Ivanovski make to microbiology?

Answer 2

discovered infectious tobacco mosaic virus

Question 3

Who was the first to discover that viruses infect bacteria?

Answer 3

Felix D’Herelle

Question 4

What exactly did Felix D’Herelle discover?

Answer 4

Bacteriophages
- he coined the term “plaque”

Question 5

Who showed that yellow fever was a virus transmitted by mosquitoes?

Answer 5

Walter Reed

Question 6

True or False:
Viruses are intracellular obligate parasites

Answer 6

True
- they need to be inside cells to replicate

Question 7

How long are typical virus genomes?

Answer 7

200,000 nucleotides = 1-200 genes

Question 8

T4 Bacteriophage infects what bacteria specifically?

Answer 8

E.coli

Question 9

What are some common exceptions to the small size of viruses?

Answer 9

Megavirus Chilensis (1200 genes)
Mimivirus (1200 genes)
Pandoravirus (2500 genes)

Question 10

What traits compose a naked virus?

Answer 10

• single or double-standed DNA or RNA (linear or circular)
• Protein shell capsid) around genome

Question 11

What are the ‘clothes’ to a naked virus?

Answer 11

possible envelope
(cell-derived membrane around the capsid)

Question 12

How is the possible envelope made?

Answer 12

taken from membrane containing structures/organelles
(ie. plasma mem, nucleus mem, mitochondria, golgi, ER, etc.)

Question 13

What is a capsid?

Answer 13

Protein shell

Question 14

What are capsids made of?

Answer 14

capsomere proteins

Question 15

A capsid and a genome together is called?

Answer 15

nucleocapsid

Question 16

Capsids are what shapes?

Answer 16

• Helical (20-sided)
• icosahedral
• irregular and complex

Question 17

Capsids are found in what folded shapes?

Answer 17

2-fold
3-fold
5-fold

Question 18

How is DNA ejected into a host cell?

Answer 18

Through the tail of a virus

Question 19

What classifies an enveloped virus?

Answer 19

a plasma membrane surrounds the nucleocapsid

Question 20

What classifies a naked virus?

Answer 20

no plamsa membrane

Question 21

What is the process of viral replication?

Answer 21

1. Adhere - stick to host cell
2. Enter
3. Uncoat - release genome
4. Synthesis - express and replicate genome
5. Assembly - create new virus particles
6. Exit - new particles leave cell

Question 22

The process of attaching to the host cell is known as a…

Answer 22

Lock and key mechanism

Question 23

What is a virion?

Answer 23

The ineffective form of a virus outside of a host cell

Question 24

How does a virus enter a host cell?

Answer 24

receptors on the plasma membrane recognize the virus

Question 25

What are some examples of cell receptors

Answer 25

HIV and CD4 receptors on T cells

Question 26

Entering animal cells is mainly different as there is no ________?

Answer 26

cell wall

Question 27

What are the two processes for entering animal cells?

Answer 27

1. endocytosis 2. membrane fusion

Question 28

What method(s) of entrance does a non-enveloped virus use?

Answer 28

endocytosis

Question 29

What method(s) of entrance does an enveloped virus use?

Answer 29

membrane fusion AND endocytosis

Question 30

At what point in endocytosis of an enveloped virus are the viral nucleocapsids released into the host cell?

Answer 30

Once the low pH of the endosome initiates fusion of the viral envelope with the endosome membrane

Question 31

How do viruses enter a plant cell?

Answer 31

depends on damage to plant tissues to open a spot in the cell wall

Question 32

What damage needs to occur on a plant for a virus to infect it?

Answer 32

- insects feeding on plants - wind damage - hail/rain damage - fire damage - human-induced damage

Question 33

How do viruses enter bacterial cells?

Answer 33

"lock and key" recognition 1. tail fibers attach to receptors 2. base of tail makes contact with host cell surface 3. inner core tube proteins extend into cell wall 4. contact with plasma mem. initiates transfer of DNA through a pore formed in the lipid bilayer

Question 34

The process of DNA entering into a bacterial cell can be known as...

Answer 34

a hypodermic syringe, where DNA's injected directly into the cell

Question 35

What are the three stages of bacteriophage replication?

Answer 35

1. lytic cycle 2. lysogenic cycle ("temperate phage")

Question 36

What does the lytic cycle contain?

Answer 36

viruses enter, replicate, and lyse host cell

Question 37

What does the lysogenic ('temperate phage") cycle entail?

Answer 37

- phage integrate genome into host cell's genome becoming a 'prophage' - prophage genome's replicated along w host cell's until stress - enters lytic phase

Question 38

Temperate phage vs lytic phage

Answer 38

- temperate phage can be both lytic or exist as prophage ('lysogeny') - lytic phage are lytic

Question 39

What are the three theories on where viruses came from?

Answer 39

1. coevolution hypothesis 2. regressive hypothesis 3. progressive hypothesis

Question 40

What is the coevolution hypothesis?

Answer 40

viruses originated about the same time as other microbes and have been coevolving with them

Question 41

What is the regressive hypothesis?

Answer 41

viruses are previously alive organisms that have evolutionarily regressed into host-dependent particles

Question 42

What is the progressive hypotheiss?

Answer 42

viruses originated from genetic material that gained the ability to replicate and be transmitted semi-autonomously

Question 43

What are plaques and what do they tell us?

Answer 43

"Clearing zones" - tell you how many virus particles were infectious in a culture

Question 44

What are some cons of cultivating bateriophages?

Answer 44

-trickier to work with than bacteria - very small - need their specific host

Question 45

What is a common method of cultivating animal viruses?

Answer 45

tissue cultures

Question 46

What are tissue cultures?

Answer 46

used to grow targets for the viruses - embryonated eggs - much less expensive

Question 47

What is the first human cell live known as?

Answer 47

HeLa cells - immortal cells

Question 48

What is the overall process of viral purification?

Answer 48

1. filtration to remove large cells and cellular debris 2. purification and concentration through centrifugation

Question 49

What are the two types of centrifugation?

Answer 49

1. differential centrifugation 2. gradient centrifugation

Question 50

What does differential centrifugation entail?

Answer 50

1. low speed centrifugation 2. transfer supernatant and centrifuge at medium speed (separates pellet of whole and broken cells) 3. transfer supernatant and centrifuge at high speed (ultracentrifugation) 4. collect pellet of virus

Question 51

What is the result of centrifugation at a medium speed?

Answer 51

pellet of whole and broken cells

Question 52

What is the result of ultracentrifugation?

Answer 52

pellet of nuclei and other large organelles

Question 53

What is gradient centrifugation?

Answer 53

dependent on different densities of viral components and particles

Question 54

What is the process of gradient centrifugation?

Answer 54

1. tube filled with layers of decreasing concentrations of sucrose 2. suspension containing virus is layered on top 3. preparation is centrifuged 4. cell debris and virus particles move to densities that they matche to