Chapter 6 Flashcards
(26 cards)
1
Q
bacteriophage
A
- also called phage
- virus the infect bacteria
- bacteriophage lambda- dsDNA virus
2
Q
virus
A
- a noncellular particle that must infect a host cell to reproduce
- It genetically subverts the cell’s machinery and directs it to produce viral particles
3
Q
virion
A
- virus particle
- consists of nucleic acid (DNA or RNA) contained within a protective protein capsid
- genomes are usually less than a dozen genes.
- must coevolve with their hosts
4
Q
host range
A
- Different viruses infect every group of organisms
- Each species of virus infects a particular group of host species
- range is usually very narrow because its genome must be very compatible with the host cell
- even specific for particular tissues or cell types
5
Q
capsid
A
- is composed of repeated protein subunits that self assemble
- packages the viral genome, protects it, and delivers it into the host cell
- Different viruses make different capsid forms
- can be divided into symmetrical and asymmetrical types
6
Q
Icosahedral viruses
A
- Symmetrical Viruses
- polyhedral with 20 identical triangular faces
- Exhibits rotational symmetry
7
Q
Filamentous viruses
A
- Symmetrical Viruses
- helical symmetry- capsid monomers self assemble into a helical tube around the genome
- The capsid consists of a long tube of protein, with the genome coiled inside
- Vary in length, depending on genome size
- Include bacteriophages as well as animal and plant viruses
8
Q
envelope
A
- encloses the capsid in some viruses
- contains glycoprotein spikes, which are encoded by the virus and allow it to recognize and infect host cells
- Common for animal viruses, rare for bacteriophage
9
Q
Asymmetrical Viruses
A
- complex multipart structures
- T4 bacteriophages
- Have an icosahedral head, helical neck, and tail fibers
10
Q
Viral genomes can be
A
- DNA or RNA
- Single- or double-stranded (ss or ds)
- Linear or circular
11
Q
Viral genes encoding viral proteins
A
- Capsid proteins
- Envelope proteins (if need be)
- Required nucleic acid polymerase not found in host cell
- Enzymes for cell lysis or virus release
12
Q
Proteomic classification
A
- compares protein amino acid sequences predicted from genome
- Statistical analysis reveals common descent of viruses with shared infected hosts
- Viruses do not have their own separate position on the tree of life
13
Q
needs for host infection
A
- Host recognition and attachment
- Genome entry
- Genome expression and replication
- Assembly of virions
- Exit and transmission
14
Q
cell-surface receptors
A
- how host recognition and attachment are mediated
- Host proteins that are specific to the host species and which are recognized by and bind to a specific viral component.
- Bacterial receptors are normally used for important functions for the host cell
15
Q
Phage Reproduction within Host Cells
A
- Most bacteriophages inject only their genome into a cell through the cell envelope.
- The phage capsid remains outside, attached to the cell surface.
- It is termed a “ghost.”
16
Q
Lytic cycle
A
- Bacteriophage quickly replicates, killing host cell
- events that threaten host cell survival trigger this cycle
17
Q
Lysogenic cycle
A
- Bacteriophage infects but becomes quiescent.
- Genome integrates into the cell’s chromosome, as a prophage
- Can reactivate to become lytic
18
Q
lysogenic conversion
A
- Prophage genes can be expressed and change host phenotype
- viral gene that encodes cholera toxin in Vibrio cholera give cholera phenotype
19
Q
Exit from cell- Lysis
A
- Phage-encoded enzyme breaks down cell wall
- must be made at the correct time after infection
- Host cell bursts to release progeny phage
20
Q
Exit from cell- Slow release
A
- Filamentous phages can extrude individual progeny through cell envelope
- Host cells do not die but grow slowly because of the metabolic burden of making virus particles
21
Q
Bacterial Host Defenses- Genetic resistance
A
Altered receptor proteins
22
Q
Bacterial Host Defenses-Restriction endonucleases
A
Cleave viral DNA lacking protective methylation
23
Q
Bacterial Host Defenses- CRISPR-CAS
A
- based on integration of short phage DNA sequences as a type of memory of previous (unsuccessful) attack
- Clustered regularly interspaced short palindromic repeats
- Cas protein complex degrades targeted viral DNA
- A bacterial immune system of sorts
24
Q
Culturing Viruses
A
- requires growth in host cells
- cultured either in batch culture (in liquid) or as isolated plaques on a bacterial lawn (on a plate)
25
one-step growth curve and the three periods
-generated by batch culture of most bacterial viruses
1. eclipse period- resembles lag phase
2. rise period- resembles log phase
3. cell lysis complete and cells burst open
26
Burst size
- the number of phages produced by a single infected cell
