Lecture 12 [Exam 3]

Question 1

Virion may contain:

Answer 1

a viral genome (DNA or RNA) contained within a protein
capsid

Question 2

True or False: capsid may or may not contain appendages (spike and tail fibers).

Answer 2

True

Question 3

____________ directs production and assembly of progeny virions

Answer 3

Phage genome

Question 4

Virions are released when the ________________.

Answer 4

host cell lyses

Question 5

__________ is the replication of bacteriophages is observed as a clear spot of lysed cells on a lawn of bacteria growing in a Petri dish.

Answer 5

Plaque

Question 6

Each plaque arises from a single _________.

Answer 6

Virion

Question 7

_______________ is the number of individual infective virions from the phage suspension (spread on the plate).

Answer 7

The plaque count

Question 8

Child infected with measles shows a ________________.

Answer 8

rash of red spots

Question 9

True or False: Some viruses integrate their genomes into the host genome and become a part of the host organism.

Answer 9

True

Question 10

A __________ is a bacteriophage that integrates its genome into the DNA of a bacterial genome.

Answer 10

prophage

Question 11

___________ is an integrated viral genome within a human cell

Answer 11

Provirus

Question 12

_____________ is a permanently integrated provirus transmitted from one human to another via the germ line.

Answer 12

Endogenous virus

Question 13

A virus may interconvert among
different forms:

Answer 13

1. Virion/virus particle
2. Intracellular replication complex
3. Viral genome integrated within
   host DNA

Question 14

A ____________ is an inert particle that consists of nucleic acid
enclosed by a protein capsid

Answer 14

Virion/virus particle

Question 15

True or False: Some virions package enzymes and
possess a lipid envelope. Does not carry out metabolism
or energy conversion.

Answer 15

True

Question 16

Within a host cell, the viral gene
products direct the cell’s enzymes
to _________________.

Answer 16

assemble progeny virions

Question 17

The virus infected cell - called a ____________.

Answer 17

Virocell

Question 18

True or False: Viral genome may integrate as a provirus
and replicate as part of the host. May be a permanent condition or reactivated to start assembling virions.

Answer 18

True

Question 19

Viruses are nonliving:

Answer 19

*The inert nature of the virion particle
* Lacks metabolism
* Lacks the ability to reproduce independent of its host

Question 20

Viruses are living:

Answer 20

• The virion assembly process

Question 21

True or False: A particular virus can infect only one species or it can affect multiple species.

Answer 21

True

Question 22

True or False: Chronic viral infections are more common than acute disease.

Answer 22

True

Question 23

_____________ keeps the viral genome intact and enables infection of the appropriate host cell

Answer 23

The structure of a virion

Question 24

A viral genome consists of either __________ or _____________.

Answer 24

DNA or RNA

Question 25

A capsid:

Answer 25

*Made up of protein *Packages the viral genome and delivers it into the host cell *Protects the viral genome from degradation * Either symmetrical or asymmetrical

Question 26

True or False: Some viruses possess a membrane envelope that is derived from membrane of the previous host cell.

Answer 26

True

Question 27

The virus envelope incorporates _________ that mediate host infection.

Answer 27

spike proteins

Question 28

The protein capsid of an enveloped virus is called a _________.

Answer 28

core particle

Question 29

Viroids are:

Answer 29

* Infectious agents simpler than viruses *Have no protective capsid *Do not code for any protein * Replicated by host RNA polymerase *Infect plants through a damaged cell wall *Some have catalytic ability

Question 30

True or False: Viroids consists of a circular, ssRNA that doubles back on itself to form base pairs interrupted by short, unpaired loops.

Answer 30

True

Question 31

True or False: The circular,ssRNA can avoid breakdown by host RNase enzymes and interacts with host cell proteins.

Answer 31

True

Question 32

_________ are an aberrant form of a normal protein arising from the host cell.

Answer 32

Prions

Question 33

True or False: Prions have no nucleic acid component

Answer 33

True

Question 34

Prions assume an __________ conformation or tertiary structure.

Answer 34

abnormal

Question 35

What do prions bind to?

Answer 35

Bind to normally folded proteins of the same class and alter their conformation

Question 36

What do prions form in the cell that ultimately leads to cell death?

Answer 36

harmful aggregates in the cell

Question 37

In the brain, prion-induced cell death leads to ______________________.

Answer 37

tissue deterioration and dementia

Question 38

To commence an infection cycle, bacteriophages contact and attach to the surface of an appropriate host cell mediated by ________________.

Answer 38

cell-surface receptors

Question 39

What are cell-surface receptors?

Answer 39

* Proteins on the host cell surface *Specific to the host * Bind to a specific viral component * Have important functions for the host cell that have been co-opted by the virus.

Question 40

Host bacteria can evolve resistance to phage attachment by __________________.

Answer 40

mutating the amino acid sequences of its surface receptors

Question 41

Host molecules that serve as a phage receptor:

Answer 41

1. LPS components 2. membrane proteins and complexes (OmpF and TolC) 3. flagellar proteins Phages bind Salmonella receptors.

Question 42

Bacteriophages deliver only their genome into a cell through the ________________.

Answer 42

cell envelope

Question 43

The empty capsid (now termed a “ghost”) remains_______________.

Answer 43

attached to the cell surface

Question 44

Bacteriophages exhibit 2 different types of replication cycles:

Answer 44

Lytic cycle and Lysogeny

Question 45

he “decision” of which replication cycle to utilize is dictated by

Answer 45

A. Environmental cues that either activate or repress transcription of genes for virus replication. B. Events that threaten host cell survival trigger a lytic burst.

Question 46

Lytic replication cycle involves:

Answer 46

*Host recognition and attachment * Genome entry * Assembly of phages * Exit and transmission

Question 47

True or False: When a phage particle delivers its genome into a cell, it immediately reproduces as many progeny phage particles as possible

Answer 47

True

Question 48

____________ are expressed first in the lytic cycle to synthesize viral proteins.

Answer 48

Early genes

Question 49

___________ expresses an enzyme that lyses the host cell wall, releasing the mature virions

Answer 49

Late genes

Question 50

_____________ is the number of virus particles released

Answer 50

Burst size

Question 51

A __________________, ex. phage lambda can infect and lyse cells like a virulent phage

Answer 51

temperate phage

Question 52

True or False: A temperate phage is also able to integrate its genome as a prophage by site-specific recombination

Answer 52

True

Question 53

A ______________ aligns the phage genome with the host DNA.

Answer 53

Recombinase enzyme

Question 54

True or False: During the exit from lysogeny the virus can acquire host genes and pass them on to other host cells.

Answer 54

True

Question 55

In the slow-release replication cycle:

Answer 55

phage particles reproduce without destroying the host cell

Question 56

The circular ssDNA serves as a template to synthesize a ____________________.

Answer 56

ds-intermediate

Question 57

True or False: A ds-intermediate slowly generates many copies of ssDNA and is packaged by supercoiling and coated with capsid proteins.

Answer 57

True

Question 58

True or False: Filamentous phages can extrude through the cell envelope during the slow release replication cycle.

Answer 58

True

Question 59

Host cells grow slowly but do not die because _____________.

Answer 59

many of its resources are diverted to virus production.

Question 60

What is the difference between lytic cycle, lysogeny, and slow-release replication?

Answer 60

Lytic involves immediate multiplication of virus, lysogeny involves viral genome will be integrated into bacterial chromosome, and slow-release is like lytic but it's a slow process

Question 61

Which cycle will be followed depends on two important factors:

Answer 61

1. The condition of the host (if cell’s growth is strong, lysogeny continues) 2. Environmental stress (ex. UV light)

Question 62

True or False: Bacteria have evolved several forms of defense against bacteriophage infection.

Answer 62

True

Question 63

What are the three ways bacteria have evolved to defend against bacteriophage infection?

Answer 63

1. Genetic resistance 2. Restriction endonucleases 3. CRISPR

Question 64

Genetic defense mechanisms involve genes that can

Answer 64

alter host receptor protein which causes the bacteriophage to fail to bind the viral coat protein or cause a different cell protein to block phage binding to the receptor.

Question 65

______________ modify their DNA by adding methyl groups to bases within certain sequences

Answer 65

Restriction endonucleases

Question 66

True or False: Bacteria can express restriction endonucleases, that cleave DNA lacking the methylated patterns (potential viral DNA)

Answer 66

True

Question 67

Where do the CRISPR short repeats come from?

Answer 67

A phage attacks which causes bacterial enzymes to destroy the phage DNA, bacteria saves a tiny piece of the phage as a CRISPR segment that is inserted as a spacer at the head of a long line of about 30 CRISPR sequences, and the the adapted host cell "remembers" infection by the specific phase.

Question 68

True or False: The next time the adapted host cell is attacked by the same phage, all of its genomic CRISPR sequences are expressed as RNA.

Answer 68

True

Question 69

The CRISPR RNA is cleaved into small sequences called ____________ containing one spacer from the original bacterial CRISPR DNA.

Answer 69

crRNA

Question 70

The crRNA binds to the ____________.

Answer 70

Cascade protein complex (or Cas complex) – endonuclease

Question 71

True or False: The Cas-crRNA complex proceeds to cleave the phage DNA, preventing phage replication.

Answer 71

True

Question 72

Phage may carry an _____________ encoding a protein Acr.

Answer 72

anti-CRISPR gene (acr)

Question 73

____________ blocks the host bacterial CRISPR-Cas from binding phage DNA.

Answer 73

Acr

Question 74

The best-known bacteriophages are in ________________________.

Answer 74

the mammalian intestinal community

Question 75

_______________ are part of a microbial community that modulates human digestion, immune system, and mental health.

Answer 75

Coliphages