Unit 2 Flashcards
What can viruses infect?
Animals, bacteria, and plants
Virus structure is composed of _________, __________, and/or __________ depending upon the type of virus.
Envelope, capsid, and genome (DNA or RNA)
Are viruses living?
No;
They need a host to infect
What are the stages of the Virulent phages Lytic Cycle?
- Attachment
- Entry
- Biosynthesis
- Assembly
- Maturation/Release (lysis)
In which stage is the viral DNA introduced into the cell in the Lytic Cycle?
Entry
In which stage of the Lytic Cycle does formation of mature viruses occur?
Assembly
The host DNA is usually degraded during which stage in the Lytic Cycle?
Biosynthesis
What would be the fate of a lytic bacteriophage if the host cell died prior to the assembly stage?
The virus would not be able to infect new hosts
What are the two types of life cycles that Temperate bacteriophages carry out?
The lytic cycle & the lysogenic cycle
What are the stages of the Temperate bacteriophages Lytic Cycle?
- Attachment
- Entry/Uncoating
- Biosynthesis
- Assembly
- Maturation/Release
What does the bacteriophages DNA form after penetration?
Lytic: circle
Lysogenic: circle; prophage
What are the two things the bacteriophages DNA can do after it becomes a circle?
Continue the lytic cycle or go on to the lysogenic cycle
What are the steps of the lysogenic cycle?
- Attachment
- Entry/Uncoating
- Synthesis
- Assembly
- Maturation/Release
(After Biosynthesis from lytic cycle)
1. Recombination: the phage DNA integrates within the bacterial chromosome
2. Induction: the prophage is excised from the host chromosome
3. Re-enters the lytic cycle
Lysogenic viral DNA which has integrated into the host genome is referred to as?
A prophage
(When the bacterium reproduces the prophage is also copied)
How can induction occur in the lysogenic cycle?
Spontaneously through recombination, some other genetic event, through UV light, or certain chemicals
How is the lytic cycle different from the lysogenic cycle with respect to the infected host cell?
The host cell dies during the lytic stage
What is the fate of the prophage during the lysogenic stage?
It is copied every time the host DNA replicates
Contact between a phage and its bacterial host occurs by _____
A random collision;
As phages are incapable of movement
What portion of bacteriophage T4 enters E. coli?
Only the T4 genome enters the bacterial cell;
The capsid remains on the surface of the cell
Once entry/uncoating into the bacterial cell has been achieved, the next step in a lytic replication cycle is _____
Synthesis
During a lytic replication cycle, what action does a phage take to ensure that its host bacterium does NOT continue synthesizing cellular molecules?
Phage enzymes degrade the bacterial DNA
In a lytic cycle of replication, release of phages involves _____
The bacterial cell bursting open;
The bacterial cell undergoes lysis, meaning that it is destroyed. Phages are then released
A major difference between the lytic and lysogenic cycles of phage replication is that during the lysogenic phase _____
The phage genome inserts itself into the host genome (prophage)
What factor may induce a prophage to enter the lytic cycle?
UV Light
During the lysogenic cycle, it is possible for integrated phage genes to change the characteristics of the host cell. This is known as _____
Lysogenic Conversion;
Lysogenic conversion involves phenotypic changes to the bacterium due to new genes from the integration of the phage genome
A basic stain has a ___ chromophore (stain-bearing ion)
Positively-Charged
Which type of stain will bond to and color bacterial cells?
A basic stain
The hanging-drop technique is very useful for observing a microbe’s __________
Motility
The normal function of the PrP protein in mammals is believed to be:
Assisting in normal synaptic development and function
How do normal prion proteins (PrP) differ from the infectious prion proteins?
Normal PrP have alpha-helices;
Infectious PrP have beta-pleated sheets
How does the number of infectious prions increase?
Prions transform normal proteins into the misfolded beta-pleated sheet configuration; therefore, prions multiply by conversion
Why are the beta-pleated multimers of PrP potentially pathogenic?
The multimers are more stable and resistant to protease
What, in a wide number of species are associated with spongiform changes in brain tissue?
Prion diseases
How can some prion diseases be transmitted?
Through the consumption of infected animal products (ex. contaminated beef or other animal products)
Which test can confirm the presence of this prion disease?
Brain Scan;
The spongiform lesions noted on the brain scan are characteristic of prion diseases
What is the typical incubation period for prion diseases?
Decades
Which are the three mechanisms that animal viruses use to enter host cells?
- Endocytosis
- Membrane fusion
- Direct penetration
What is Endocytosis?
When the virus is engulfed by the host cell into a vesicle, then the viral genome is released into the cell
What is Membrane fusion?
When the viral envelope fuses with the host cell membrane, allowing the viral capsid and genome to enter the cell
What is direct penetration?
When the viral capsid attaches to the host cell membrane, and the viral genome is injected directly into the cell
What is the difference between membrane fusion and endocytosis?
In membrane fusion, the cell does not surround the virus with cell membrane
A latent virus:
Can remain in the host for an extended time without causing any signs or symptoms;
Not all latent viruses insert into the host chromosome like prophage. If they DO, they cannot leave (unlike prophages)
What is the first step to occur in HIV replication?
Reverse transcriptase makes DNA from a viral RNA template;
HIV has +ssRNA genome. Therefore, the RT uses it to make a complementary strand of viral DNA
Which HIV enzyme is responsible for production of functional enzymes and capsomeres from a very large polypeptide?
Protease
What is an example of a Latent viral infection?
Shingles caused by the herpes zoster virus
(1) What is the correct sequence of events for the replication of a DNA virus?
Virions attach to the host cells
(2) What is the correct sequence of events for the replication of a DNA virus?
Viral DNA is released into the nucleus of the host cell
(3) What is the correct sequence of events for the replication of a DNA virus?
Enzymes required for multiplication of viral DNA are produced via transcription and translation and viral proteins are synthesized
(4) What is the correct sequence of events for the replication of a DNA virus?
A copy of the DNA is made and the virions are assembled
(5) What is the correct sequence of events for the replication of a DNA virus?
Capsid and other structural proteins are manufactured and virions mature
(6) What is the correct sequence of events for the replication of a DNA virus?
Assembled virions are released from the host cell
What disease does the human herpesvirus-1 cause?
Cold sores or fever blisters;
Painful, short-lived vesicles that form near the outer margins of the lips. Transmitted via oral and respiratory routes
What happens to the Gram-positive cell wall during decolorization?
The decolorizing agent dehydrates the peptidoglycan but the color stays
What happens to the Gram-negative cell wall during decolorization?
The decolorizing agent dissolves the outer membrane and removes the color
As bacterial cells age, their peptidoglycan begins to break apart. What would be the effect on decolorization?
Old Gram-positive cells will be decolorized
How does safranin affect Gram-positive cells?
Safranin penetrates the cell wall, but is masked by the darker crystal violet stain
