(6-13) Viruses of Bacteria-- Bacteriophages

Question 1

Viruses can infect organisms of which domain?

Answer 1

Viruses can infect all 3 domains.

Question 2

A virus particle is called a _______.

Answer 2

Virion

Question 3

A virion consists of what 2 parts?

Answer 3

Nucleic acid surrounded by protein coat

Question 4

A viral protein coat is called what?

Answer 4

Capsid

Question 5

What is a capsid composed of?

Answer 5

Capsomers

Question 6

What are the 3 virusal shapes?

Answer 6

1. Isometric
2. Helical
3. Complex

Question 7

Describe the viral genome, including its nucleic acid, shape, and strand characteristics.

Answer 7

1. Contains either DNA or RNA
2. Can be linear or circular
3. Single stranded or double-stranded

Question 8

Why can viruses only multiply inside metabolizing cell?

Answer 8

Viruses use host machinery to support their reproduction.

Question 9

Every virus contains information to perform which 3 tasks?

Answer 9

1. make viral proteins
2. assure replication
3. move in/ out of host cells

Question 10

What 2 phases do viruses live in and what is their metabolic state in each phase?

Answer 10

1. Extracellular phase (Metabolically inert)

2. Intracellular phase (“Metabolically” active)

Question 11

What are the six stages of the Lytic Cycle?

Answer 11

1. Adsorption
2. Penetration
3. Transcription
4. Replication
5. Assembly (or maturation)
6. Release

Question 12

What occurs during the Adsorption stage of the Lytic Cycle?

Answer 12

1. The phage collide by chance with E. coli
   ~ Remember viruses are metabolically inactive
2. Protein fibers on phage attach to specific receptors on E. coli
   ~ Receptors perform other function on cell, but phage co-ops for own purpose
   ~ T4 attaches to a permease in the outer membrane of E. coli

Question 13

What occurs during the Penetration stage of the Lytic Cycle?

Answer 13

1. Lysozyme located at tip of phage tail degrades E. coli cell wall
2. Tail contracts and double stranded DNA is injected through phage tail into cell
3. Protein coat remains outside

Question 14

What occurs during the Transcription and Replication stages of the Lytic Cycle?

Answer 14

1. Phage DNA transcribed into mRNA and translated into proteins
2. Phage takes over metabolism of cell
3. Not all phage proteins synthesized simultaneously

Question 15

Describe the synthesis of early viral proteins during the Lytic Cycle.

Answer 15

Early viral proteins are synthesized first and are associated with the replication of viral nucleic acid
Ex. a nuclease that degrades E. coli DNA

Question 16

Describe the synthesis of late viral proteins during the Lytic Cycle.

Answer 16

Late viral proteins are synthesized and are associated with the replication of other viral structures
Ex. capsid proteins, lysozyme to lyse bacteria

Question 17

Describe the concept of self-assembly, with respect to the Lytic Cycle.

Answer 17

The protein components come together spontaneous due to the specific shape of the caspomers.

Question 18

The Assembly Stage of the Lytic Cycle is also called _________.

Answer 18

Maturation

Question 19

What occurs during the Assembly stage of the Lytic Cycle?

Answer 19

1. Phage head is formed
2. DNA is packed in head
3. Tail is attached
4. Tail fibers attached

Question 20

What occurs during the Release stage of the Lytic Cycle?

Answer 20

1. Lysozyme synthesized
2. E. coli bursts and releases phage to environment
   [In the case of T4, 200 phage are released in about 30 minutes]

Question 21

How do some viruses pick up their envelope as they leave the host cell?

Answer 21

The envelope is made of a portion of the host cell plasma membrane which becomes the lipid envelope of the virus.

Question 22

Describe 2 ways the Λ (Lambda) Phage may interact with E. coli.

Answer 22

1. Λ can go through productive lytic infection (like T4)

2. Λ can be a temperate phage

Question 23

How can the Λ Phage “Live in harmony” with E. coli?

Answer 23

1. During the Lysogenic cycle, the Λ Phage integrates into a specific site in the E. coli genome (between gal and bio genes)
2. If E. coli growing slowly (low nutrients) the Λ Phage will integrate.
3. If bacteria gets damaged (ex. by UV light), Λ DNA is excised and lytic cycle progresses.

Question 24

What are the 2 types of transduction that occur with bacteriophages?

Answer 24

1. General Transduction

2. Specialized Transduction

Question 25

What is the difference between general and specialized transduction in bacteriophages?

Answer 25

1. General ~ Any gene from fragmented bacterial genome can be transferred to new bacteria 2. Specialized ~ Transfer of only a few specific genes ~ If Λ phage excises imprecisely from bacteria, may carry either gal gene or bio gene

Question 26

Define the Host Ranges of Phages.

Answer 26

Number of different bacteria that phage can infect termed host range

Question 27

Why are Host Ranges of Phages usually limited to a single bacterial species for a single phage?

Answer 27

Phage must be able to attach to host receptors.

Question 28

What are the 2 ways receptors on bacterial surface can be altered?

Answer 28

1. Receptor sites can be altered by mutation | 2. Lysogenized bacteria can alter cell surface (alteration of receptor site)

Question 29

How does virus interaction affect a bacterium?

Answer 29

The effect on bacteria cells depends on infecting phage

Question 30

Which type of productive infection does not lyse the cell, but keeps it alive?

Answer 30

Extrude viruses | ~ Ex. M13 virus of E. coli

Question 31

Which type of productive infection kills the cell by bursting?

Answer 31

Lytic Phages | ~ Ex. T4 virus of E. coli

Question 32

What is a productive infection?

Answer 32

When phage multiply inside cell, producing numerous progeny (more viruses are produced).

Question 33

When some phage integrate into host genome, it is termed ________, which means, "______"

Answer 33

1. temperate | 2. controlled

Question 34

Which type of infection is termed latent because there may be no sign of infection?

Answer 34

Temperate

Question 35

The bacteria carrying a temperate phage is termed a _______.

Answer 35

Lysogen

Question 36

The phage that is integrated within a Lysogen is termed a __________.

Answer 36

Prophage | ~ Ex. Lambda (Λ) virus of E. coli

Question 37

How does a Lambda virus remain lysogenic (temperate) within an E. coli bacterium?

Answer 37

1. Protein sticks to DNA 2. Repressor sticks to promotor region & prevents Lambda from being excised. 3. If damaged by UV light, repressive no longer works and Lambda virus can be released. 4. Released Lambda will then enter lytic cycle.